Equation of State and Amorphization of Ca9R(VO4) - ACS Publications

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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

Equation of State and Amorphization of Ca9R(VO4)7 (R = La, Nd, Gd): A Combined High-Pressure X‑ray Diffraction and Raman Spectroscopy Study Katarzyna M. Kosyl,*,† Wojciech Paszkowicz,† Olga Ermakova,† Damian Wlodarczyk,† Andrzej Suchocki,†,‡ Roman Minikayev,† Jaroslaw Z. Domagala,† Alexei N. Shekhovtsov,§ Miron Kosmyna,§ Catalin Popescu,∥ and François Fauth∥ Downloaded via UNIV OF TEXAS SW MEDICAL CTR on October 11, 2018 at 16:38:43 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

†

Institute of Physics, Polish Academy of Sciences, Aleja Lotników 32/46, 02-668 Warsaw, Poland Institute of Physics, Kazimierz Wielki University, Weyssenhoffa 11, 85-072 Bydgoszcz, Poland § Institute for Single Crystals, NAS of Ukraine, Nauky Avenue 60, 61001 Kharkov, Ukraine ∥ CELLS-ALBA Synchrotron Light Facility, 08290 Cerdanyola, Barcelona, Spain ‡

S Supporting Information *

ABSTRACT: Ca9R(VO4)7 (R = rare earth) multicomponent oxides of a whitlockite-related structure are under consideration for applications in optoelectronics. In this work, the Czochralski-grown Ca9R(VO4)7 crystals were investigated as a function of pressure by powder X-ray diffraction and single-crystal Raman spectroscopy. The diffraction experiments were performed at the ALBA synchrotron under pressures ranging up to 9.22(5), 10.7(1), and 8.55(5) GPa for R = La, Nd, and Gd, respectively, to determine the third order equation of state (EOS) parameters. Fitting of the Birch−Murnaghan EOS provided the isothermal bulk moduli K0 = 63(4), 63(2), and 61(5) GPa for these three orthovanadates. These values are apparently lower than that reported for structurally related tricalcium vanadate Ca3(VO4)2. The compressibility anisotropy was observed; the lattice is markedly stiffer in [001] than in [100] direction. For Ca9Nd(VO4)7, the variation of the diffractograms just above 10 GPa provides an indication on the beginning of amorphization process; during pressure release the whitlockite-like structure is recovered. Raman spectroscopy measurements for single crystals of the above-mentioned rare-earth vanadates and Ca9Y(VO4)7 were performed (the maximum pressures achieved were 16.3(1), 21.2(1), 15.3(1), and 18.6(1) GPa for R = Y, La, Nd, and Gd, respectively). These measurements reveal a partially reversible phase transition interpreted as amorphization, with an onset at the pressure of ∼9−10 GPa, characterized by broadening of the peaks and their shift to lower energies.

1. INTRODUCTION Whitlockite, named after Herbert Percy Whitlock (1868− 1948), American mineralogist, is a mineral of the idealized formula Ca9(MgFe2+)(PO4)6PO3OH. Synthetic and natural materials crystallizing in related structures form an extended family of compounds, including multiple phosphates, vanadates, and several arsenates. All members of the whitlockite family (except the below-mentioned tuite) crystallize in R3c space group with the unit cell size of a ≈ 10−11 Å, c ≈ 37−39 Å. One of representative anhydrous minerals from this family is merrillite (idealized formula Ca9NaMg(PO4)7), found at lunar and Martian meteorites (several variants of merrillite, differing by chemical composition, are known).1,2 Merrillite can be also produced by shock transformation from whitlockite.3,4 Composition of merrillite is close to tricalcium phosphate (β-Ca3(PO4)2, TCP). A vanadium-based synthetic tricalcium vanadate homologue (Ca3(VO4)2, TCV) is isostructural. Both can be treated as parent compounds of various (structurally © XXXX American Chemical Society

and chemically close to merrillites) anhydrous compounds in the whitlockite family. Regarding the Ca3(XO4)2 formula, usually written in equivalent way as Ca10.5(XO4)7, a part of Ca2+ ions can be replaced by other cations, like Na+, Mg2+, Fe2+/3+, Pb2+, Bi3+, R3+. In the latter case, for X = V, Ca9R(VO4)7 oxides are formed. The site occupation scheme in the Ca9R(VO4)7 is mostly similar to that of Fe-merrillite (the synthetic Ca9Fe3+(PO4)7 was reported for the first time in ref 5). Within the Ca9R(VO4)7 and Ca9R(PO4)7 series, the partial occupation of different Ca sites is specific for each rare earth.6−12 Some of these materials are considered for applications in optoelectronics, for example, in tunable light-emitting diodes,13−15 nonlinear optics, and laser materials.16 Because of the non-centrosymmetric crystal structure of whitlockite,17 structurally related compounds are expected to Received: April 30, 2018

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DOI: 10.1021/acs.inorgchem.8b01182 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry be efficient second-harmonic generation materials.18 The high nonlinear susceptibility of these compounds is related to electron structure of V5+ ions, having large density of d-bands states. The V−O bond is covalent and has larger polarization ability in comparison to typical ionic bonding.19 Unfortunately, dopants, defects, and nonoptimum conditions of growth and post growth annealing can induce essential internal stresses in crystals and affect the nonlinear susceptibility dramatically. Determination of structural, elastic (such as thermal expansion, bulk modulus), and vibrational properties may be helpful for further progress of science and technology involving these materials. As for the thermal expansion of Ca9R(VO4)7 and some other whitlockite-related multicomponent oxides, the information has been reported in recent years (see ref 20 and refs therein). Currently, the behavior under compression for the rareearth-containing, whitlockite-related vanadates is unknown (the only in situ diffraction study has been reported for the parent TCV).21 We find it useful to briefly discuss throughout the paper also the data available for closely structurally connected orthophosphates. Among the whole whitlockite family and other compositionally related phosphates, there are only a few experimental (e.g., X-ray diffraction (XRD) and Raman spectroscopy) and theoretical studies under high pressure, namely, for structurally related and unrelated polymorphs of Ca3(PO4)2 (TCP),22−28 for Mg-doped β-TCP,29 and apatites Ca5(PO4)3X (X = OH, F, Cl).30 On the basis of in situ XRD results for β-TCP, in the studied pressure range (up to 15.4 GPa) there is no phase transition for this material.25 In studies achieving higher pressures, amorphization for β-TCP has been observed at 21 GPa.23 For Mg-doped tricalcium phosphate (β-TMCP) a reversible transition to an amorphous phase has been revealed by XRD at pressure of ∼32 GPa but has been reported as irreversible when the pressure of ∼57 GPa has been achieved.29 Highpressure Raman spectra have been recorded for β-TCP twice: up to 20.822 and 18 GPa;28 in the former case an irreversible amorphization has been observed. The γ-TCP phase of a unit cell size similar to that of β-TCP, but of a different space group (mineral name tuite, R3̅m space group, Z = 3) has been reported to form either from whitlockite or by decomposition of apatite at high pressures (7 to 15 GPa in experiments, 2.5 GPa from theory) accompanied by high temperatures (1300 to 2300 °C in experiments, 1000 °C from theory); γ-TCP has been also found to form at static pressure or by shock event as happens in meteorites.3,26,31−34 The TCV exhibits a structure similar to β-TCP (at ambient temperature) up to pressures of ∼10 GPa, at which the amorphization has been detected by both energy-dispersive XRD and Raman spectroscopy measurements, showing simultaneous broadening and disappearing of the peaks.21 In the cited work, a detailed analysis of diffraction and vibrational phenomena clarified the nature of the transition from crystalline to amorphous phase. The behavior under combined high pressure and temperature may be different: applying p = 11 GPa and T = 1373 K leads to formation of a new TCV phase (C2/m space group), crystallizing in a structure related to that of Pb3(VO4)2.35 Among those crystals of composition and structure related to the β-TCP or TCV, for which some Ca sites are partially occupied by rare earths, the Raman spectra have been reported for Ca3−3xNd2x(XO4)2 (X = P, V) in a broad temperature range,36 as well for Ca9Nd(VO4)7 and Ca3−1.5x−yEuxCuy(VO4)2 at ambient conditions.16,37 In the latter case, a reversible high-temperature

phase transition has been reported.36 For several vanadate whitlockites, namely, for TCV21 and Ca10M(VO4)7 (M = Li, Na, K),38 the factor group analysis has been performed. To the best of the authors’ knowledge, no high-pressure XRD and Raman spectroscopy investigations have been reported for any Ca9R(VO4)7 materials. In this work, high-pressure powder XRD was performed for three compounds exhibiting the merrillite-related structure Ca9R(VO4)7 (R = La, Nd, Gd), to obtain equation of state (EOS) parameters. Additionally, Raman spectra were examined under pressure for tiny single crystals of these orthovanadates and for Ca9Y(VO4)7 under pressure, to get additional information about the vibrational behavior and on possible phase transitions.

2. EXPERIMENTAL SECTION The crystals were grown from dried high-purity components (CaCO3, R2O3, and V2O5). The growth process of Ca9R(VO4)7 (R = Y, La, Nd, Gd) was performed by the Czochralski method in argon atmosphere. The material was melted in Ir crucibles (diameter = 60 mm, length = 70 mm). Seeds oriented along [001] direction were used. For growth details see ref 39. Phase purity was verified for the samples ground in agate mortar, using a modern laboratory diffractometer (X’Pert PRO Alpha-1, PANalytical). Synchrotron radiation experiments were performed on the highpressure/microdiffraction station of the BL04-MSPD beamline of the ALBA synchrotron (Barcelona area).40 A monochromatic X-ray beam (λ = 0.4246 Å) was focused down to 15 × 15 μm2 (full width at halfmaximum (fwhm)) by using Kirkpatrick−Baez mirrors. An Inconel X750 metal gasket with a central hole of 300 μm diameter was preindented to a thickness of 55 μm and used as a sample chamber. A mixture of methanol−ethanol in 4:1 ratio was employed as pressure transmitting medium (PTM). The pressure was determined by the ruby fluorescence method. High-pressure XRD experiments were performed using an Almax-Boehler plate diamond anvil cell equipped with 700 μm diamond culet.41 The two-dimensional XRD patterns were collected by a Rayonix CCD detector. The Debye−Scherrer rings were integrated using the Fit2D program,42 and then the Le Bail fitting was performed employing FullProf.2k (version 5.80) program.43 Pressure−volume (p−V) data were fitted using the Birch−Murnaghan (B.-M.) equation with the EoSFit7c program,44 to determine the equation of state (EOS) parameters. The Raman spectra were measured at room temperature using a MonoVista CRS+ Raman system equipped with 532 nm laser. For ambient pressure, a 100 μm slit and 50× long working distance (LWD) objective was used. The acquisition time was 10 s (each spectrum was averaged from two measurements at the same pressure). For the high-pressure measurements, the polished samples with a thickness of ∼25 μm were placed in the Diacell CryoDAC-LT (Almax easyLab). Argon was applied as a PTM, and ruby was used as a pressure gauge. The uncertainty in the pressure determination by means of ruby fluorescence, for both XRD and Raman spectroscopy techniques, is evaluated as 0.05 GPa for pressures below 10 GPa, and 0.1 GPa above. A 5× LWD objective was used in the pressure-dependent measurements. The data acquisition time varied from 30 to 60 s (again, average of two spectra), and resolution was better than 1 cm−1.

3. RESULTS The phase analysis based on XRD data collected with a conventional laboratory diffractometer has shown that the Ca9R(VO4)7 samples crystallized in R3c space group and did not contain any spurious phases. The refined lattice-constant values (a = 10.8959(2) Å, c = 38.1416(7) Å for R = La; a = 10.86540(5) Å, c = 38.1279(2) Å for R = Nd; a = 10.85774(4) Å, c = 38.0881(2) Å for R = Gd) differ by less than 0.1% from those reported earlier in refs.6,8 The ambient-pressure structure was B


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Inorganic Chemistry

Figure 1. X-ray diffractograms of Ca9R(VO4)7 (R = La (a), Nd (b), Gd (c)) during compression (up to a dashed line) and decompression (above the dashed line). For clarity, the background was subtracted. The pressure values are set at the right axis; pressures marked with asterisks refer to data collected during decompression. The uncertainty in the pressure determination is 0.05 GPa for pressures below 10 GPa, and 0.1 GPa above.

conserved during all compression steps, except for those just above 10 GPa regarding the Ca9Nd(VO4)7 crystal, in which the transition onset is seen (Figure 1): a significant broadening of the diffraction peaks is observed (resulting in disappearing of the most of low-intensity ones) with background simultaneously rising up in the 7° to 10° 2θ range, in the vicinity of diffraction maxima corresponding to d ≈ 3 Å (Figure 2). The increased background represents the amorphous fraction of the sample at the given pressure. Together with the described changes, some diffraction peaks tend to disappear, suggesting yet unrecognized structural effect. Mentioned above alterations in diffractograms are reversible, with a relatively large hysteresis of ∼3−4 GPa. Because of large broadening and overlap of the peaks, the Le Bail fitting could not be performed effectively for the highest levels of compression. In case of Ca9La(VO4)7 and Ca9Gd(VO4)7, pressures above 10 GPa were not achieved. Therefore, the transition onset is not observed for these crystals. The unit-cell size was fitted through Le Bail refinement using the low-angle part of the diffractograms, where the peak overlap is limited (for representative fitting results see Figure 3; the values of lattice parameters are available in the Supporting Information, Table S1). On the basis of Figure 4, showing relative changes of the lattice parameter, we can clearly see that all crystals exhibit anisotropic compressibility: they are stiffer (less compressible) along the [001] direction as compared to [100] direction. This property can be quantified in a different manner, using the concept of “linear modulus”, M0, evaluated

Figure 2. Selected X-ray diffractograms of Ca9Nd(VO4)7 near the onset of the phase transition and during decompression. For description of the right axis see the legend of Figure 1.

by following the way described in ref 44 (the cubed lattice constant is considered instead of the unit cell volume in EOS calculationsfor simplicity second order of B.-M. equation was used). The obtained M0a and M0c values (for the a(p) and c(p) data) are as follows: 168(3) and 250(8) GPa for R = La; 184(4) and 267(4) GPa for R = Nd; 180(4) and 284(5) GPa for R = Gd, respectively. In each case, M0c is larger by a factor of ∼1.5 than M0a. C


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Inorganic Chemistry

Figure 3. Le Bail refinement results for Ca9R(VO4)7 (R = La (a), Nd (b), Gd (c)) (data with subtracted background). Red crosses are assigned to experimental data, and black lines refer to calculated profile; blue vertical bars refer to Bragg reflections, and blue solid line is the difference pattern between experimental and calculated data. The reliability factors (Rp, Rwp, in percentage) of the above refinements are as follows: (15.5, 18.8), (9.32, 13.6), and (9.68, 13.4) for R = La, Nd, and Gd, respectively.

room conditions, reveals some apparent differences in band signal ratio, probably related to specific distribution of the given rare earth throughout the lattice sitessome modes are clearly more distinguishable than the others. The high-pressure spectra exhibit a perceptible broadening with rising pressure, accompanied by increasing overlap between various modes, due to disordering of the nonequivalent calcium sites with different local coordination spheres. Consequently, the spectra gradually become irresolvable: fewer lines can be distinguished and be traced at higher pressures (see Figures 8 and 9 for the spectra recorded during compression and decompression, respectively). To record the pressure dependence versus positions of the lines, they were decomposed into Gaussian bands. Linear fit parameters of the signal positioning versus pressure are shown in Table 2. The mode at ∼150 cm−1 is characteristic for all of the investigated materials (in case of Ca9Nd(VO4)7, the 157 cm−1 mode is visible only under magnification) and virtually does not move with the pressure, except in R = La case. The rest of the low-energy part cannot be resolved unambiguously because of the modes that are overlapping with the signal from Ar. Up to ∼8−9 GPa all other peaks in the spectra shift toward higher energies, with quite divergent rate ranging from 0.86 to 10.74 cm−1/GPa. Some of the lines (for R = Y a line at 853 cm−1; R = La: 847, 850, 854 cm−1; R = Nd: 851 cm−1; R = Gd: 863 cm−1) with significantly higher upshift rate (from 5.01 to 7.16 cm−1/GPa)

The pressure dependence of the lattice constants for studied Ca9R(VO4)7 compounds is characteristic: the c(p) variation is nearly linear, resembling the behavior visible in Figure 2 in ref 21 for TCV, whereas a(p) behaves more like a concave curve. Combining these two dependencies, the c/a ratio (Figure 5) is strongly nonlinear. Fitted equations of state match well the experimental V(p) data (cf. Figure 6). The good fit quality, indicated by the χ2-based practical rules proposed in ref 45, permitted to consider the third-order B.-M. EOS (the obtained χ2 value for R = La, Nd, and Gd is 2.72, 1.24, and 2.36, respectively). The obtained EOS parameters are quoted in Table 1 (the secondorder EOS fit is reported as well, for comparison). The slope of the V(p) curve is larger for Ca9R(VO4)7 than for Ca3(VO4)2. This discrepancy is attributed to the difference in chemical composition. It is not excluded that the difference in applied PTM contributes to the discrepancy, as well. The fitted zeropressure unit cell volumes from the third-order of B.-M. EOS match quite well the values determined at ambient conditions (VAC) for the samples by a classical Bragg−Brentano technique: the discrepancy does not exceed 0.3%. The isothermal bulk moduli for studied compounds are K0 = 63(4), 63(2), and 61(5) GPa for R = La, Nd, and Gd, respectively. Raman spectra of Ca9R(VO4)7 (R = Y, La, Nd, Gd) crystals at ambient pressure contain two main groups of bands; at range of 50−500 cm−1 and more intensive ones at ∼700−950 cm−1 (see Figure 7). Comparison between all spectra, collected at D


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Inorganic Chemistry

Figure 4. Variation of relative lattice parameters with pressure for Ca9R(VO4)7 (R = La (a), Nd (b), Gd (c)). Solid symbols/pluses represent the relative values of a parameter (during compression/decompression). Respectively, the empty symbols/crosses are related to changes of c parameter. Solid lines are drawn as a guide. The estimated errors are smaller than the symbol size.

Figure 5. Axial ratio c/a vs pressure for Ca9R(VO4)7. R = (■) La, (▲) Nd, (●) Gd. The guide solid lines shown in the figure were obtained by fitting the function f + g·exp(h·p), where p = pressure (in GPa). The fitted parameters ( f, g, h) are (3.542, −0.048, −0.34), (3.551, −0.042, −0.31), and (3.559, −0.054, −0.29) for R = La, Nd, and Gd, respectively.

Figure 6. Experimental p−V data and fitted third-order B.-M. EOS for Ca9R(VO4)7. R = (■) La, (▲) Nd, (●) Gd. Blank symbols are related to the unit cell volumes during decompression (these points were not included in the calculation of EOS). (inset) A comparison of the fitted EOSs for Ca9R(VO4)7 (solid lines) with TCV high-pressure data (×) from ref 21 (connected with a dashed guide line). The uncertainties are smaller than the symbol size.

outpace the most intensive modes (868, 861, 866, and 867 cm−1 in the R = Y, La, Nd, and Gd series) with common pressure coefficients (ranging from 2.31 to 3.00 cm−1/GPa). As visually

observed, this process starts somewhere above 3 GPa. A representative example of Raman mode positioning variation with applied pressure is presented for Ca9Y(VO4)7 in Figure 10. E


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Inorganic Chemistry Table 1. Fitting Results of the Birch-Murnaghan EOS Parameters for Ca9R(VO4)7 (R = La, Nd, Gd)a compound

space group

pressure transmitting medium

Ca9La(VO4)7

R3c

MEc

Ca9Nd(VO4)7

R3c

MEc

Ca9Gd(VO4)7

R3c

MEc

Ca3(VO4)2

R3c

silicone oil

β-Ca3(PO4)2

R3c

liquid He

β-TMCP

R3c

silicone oil MEWf

α-Ca3(PO4)2g γ-Ca3(PO4)2h

P21/a R3̅m

VACb [Å3]

V0 [Å3]

WHITLOCKITE-RELATED CRYSTALS 3921.51(12) 3921(4) 3921(6) 3898.20(3) 3886(2) 3893(3) 3888.66(3) 3870(4) 3879(7) 3874.2(3.6) 3876.8(5.1) 3508.4(6.2) 3527.26 3471.8(3.5) (at 0.25 GPa)

K0 [GPa]

K′

63(1) 63(4) 69.2(7) 63(2) 69(1) 61(5) 99.08(2.25) 92.50(8.23) 79.5(2.0) 82.0e 96.7(4.9) 83.4(1.1) 80.6(3.1)

4d 4(1) 4d 5.6(6) 4d 6(1) 4d 5.89(2.38) 4d 7.4(1.0) 4d 4.8(5)

this this this this this this 21 21 25 27 23 29 29

75.9e 113.1(12) 100.2(13)

4.00d 4.00d 5.48(16)

27 24 24

ref work work work work work work

CRYSTALS OF DIFFERENT SYMMETRIES c

ME

a

Parameters of the 2nd order EOS obtained in this work are given in italics. bAmbient conditions. cMethanol−ethanol mixture. dImplied value. Calculated using ab initio density functional methods. fMethanol−ethanol−water mixture. gHigh-temperature phase of Ca3(PO4)2. hHighpressure phase of Ca3(PO4)2. A comparison with earlier reported data for structurally and compositionally-related materials. e

between 0.149 and 1.494. At the low-energy region (up to 500 cm−1), some modes appear with high Grüneisen parameter value. Similar ones were found in two materials mentioned beforetuite and TCV.26,21 In the case of spectral region related to V−O stretching modes and V−O−R transitional oscillations (between 700 and 1000 cm−1) Grüneisen parameters were found to be consistent with those already known from literature regarding calcium phosphates,26,28 vanadate,21 as well as for strontium phosphate.46 The cited and present values range mostly from 0.2 to 0.5. As noticed in the Introduction, for structurally related materials, a reversible or irreversible amorphization has been observed in literature, depending on the material and pressure applied. The initial spectral features of the studied Ca9R(VO4)7 crystals are partially restored during decompression (Figure 9). Apparently, with lowering the pressure fwhm of the lines tends to decrease, but the initial width is not fully restored, and a certain hysteresis of ∼5 ± 2 GPa (similar to that derived in the XRD part of this study) is observed. Therefore, it is likely that the observed phase transition is partially reversible. The abovedescribed unique modes for Ca9Nd(VO4)7 are visible again at pressures 2.11(5) and 0.39(5) GPa in contrast to Ca9La(VO4)7, where such peaks were not detected.

Figure 7. Raman spectra of Ca9R(VO4)7 (R = Y, La, Nd, Gd) collected at ambient conditions (with subtracted background and normalized according to the strongest band).

Peaks at pressures of ∼9−11 GPa, especially the strongest ones at wavenumbers between 700 and 900 cm−1, become markedly broader and shift toward lower energies, indicating a phase transition. In the case of Ca9Nd(VO4)7, sharp lines are observed around 430 and 670 cm−1 at pressures between 5 and 7 GPa. To be sure about the material-related origin of those lines, the measurement was repeated on another piece of crystal, revealing the same behavior. Some nonintentional, low-level impurity from other rare earths could cause such behavior, but the real origin of those peaks requires more detailed studies. Lines having trace intensity with similar energies were found in Ca9La(VO4)7 spectrum at 2.08(5) GPa (visible only at a high enlargement). For Ca9R(VO4)7 (R = La, Nd, Gd), the Grüneisen parameters were derived from the Raman line positions and bulk moduli from third-order EOS obtained via XRD measurements (Table 1), giving values in a broad range

4. DISCUSSION The present study aims for description of elastic and vibrational properties in Ca9R(VO4)7, as well as for comparison of these properties with those regarding to parent vanadate and other structurally related phosphates. The compositional and structural differences between earlier studied Ca3(VO4)2 (equivalent to Ca10.5(VO4)7 formula) and Ca9R(VO4)7 are relatively small. As for the composition, one among 10.5 Ca atoms in the TCV formula is replaced by rare earth, 0.5 Ca atomby structural vacancies. In the unit cell, the R atoms and vacancies substitute the Ca ions at specific sites; the volume of the new unit cell differs from the old one by less than 2%. Therefore, the analysis of the structural and F


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Inorganic Chemistry

Figure 8. Unpolarized Raman spectra of Ca9R(VO4)7 (R = Y (a), La (b), Nd (c), Gd (d)) crystals as a function of pressure at room temperature, during compression (subtracted background). The pressure values are set at the right axis. The error in the pressure determination is 0.05 GPa for pressures below 10 GPa, and 0.1 GPa above. Because of significant decrease of the signal intensity with rising pressure, all the spectra were normalized to the height of the strongest peak, to facilitate observing the spectral features. The arrows crossing the local maxima are guide indicators showing the direction of variation in positions of these maxima. The encirclements indicate the additional narrow peaks observed for Ca9Nd(VO4)7.

(quoted in Table 1) are 61(5), 63(2), and 63(4) GPa, respectively; taking into account the evaluated uncertainties these bulk modulus could be considered as subequal. The following reasons can contribute to this observation: - For the studied Ca9R(VO4)7, the molar content of R element is much smaller than in the RVO4 series (rare earth cationic fraction 0.059 instead of 0.500), so the variation of the K value plotted against the unit cell volume is expected to be marginal. Therefore, it is excepted that the experimental uncertainties in K0 (between 2 and 5 GPa) mask the monotonic variation. - The Ca9R(VO4)7 orthovanadates are considered as oxides of disordered structure, where the R atoms share the positions with Ca, but the occupancies at each site are known to strongly depend on the choice of the R component atom. This is a structural difference between Ca9La(VO4)7, Ca9Nd(VO4)7, and Ca9Gd(VO4)7, which may influence the experimental K0 value. To analyze the compressibility, the relative reductions of the a and c unit cell parameters were compared for pressures ranging to 8 GPa, that is, up to the value at which TCV is still crystalline. For R = La, Nd, and Gd, the reduction of a value is 3.7%, 3.3%, and 3.5%, whereas that for c value is 2.7%, 2.5%, and 2.4%, respectively. Thus, these crystals are stiffer in the c direction. Related values for TCV are 2.1% for a and 2.7% for c (these values are derived from Figure 2 in ref 21). In other words, the axial ratio for these three Ca9R(VO4)7 compounds

elastic data within the Ca9R(VO4)7 family and comparison to the parent Ca3(VO4)2 orthovanadate requires a particular care. Incorporation of rare earths into the Ca3(VO4)2 proceeds in a complex way, as the R atoms share the occupation of typically three different sites with the host Ca atoms. The unit cell includes structural vacancies that are absent in TCV; the vacancies are a likely factor resulting in a bulk modulus reduction in respect to that of TCV. Namely, for the studied crystals, its value is ∼61−63 GPa, that is, lower than that for TCV (equal to 92.50(8.23) GPa, from third-order EOS).21 This finding may require a confirmation, as the only available data for TCV have been obtained using the silicone oil as PTM (this medium does not provide hydrostatic conditions at higher pressures,47,48 so it may lead to overestimation of the K value). Generally, in a series of isostructural oxides, the bulk modulus can be expected to linearly decrease when plotted against increasing cell volume (see ref 49). An example of such behavior among rare-earth-containing orthovanadates is the series of LuVO4−EuVO4 orthovanadates (zircon structure type), in which the value of K0 (provided by an empirical model) decreases along the lanthanide series from 145 to 134 GPa (cf. Table 2 in ref 50). As for the studied Ca9Gd(VO4)7, Ca9Nd(VO4)7, and Ca9La(VO4)7 whitlockite sequence, the unit cell volume gets larger (due to increasing ionic radius of rare earth atom); therefore, an analogous linear decrease of K0(V) could be expected. The present results do not show such clear behavior; in this case the K0 values G


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Inorganic Chemistry

Figure 9. Raman spectra of Ca9R(VO4)7 (R = Y (a), La (b), Nd (c), Gd (d)) crystal collected during decompression (subtracted background). For description details see the legend of Figure 8.

increases by ∼1.0% under 8 GPa pressure (see Figure 5), whereas for TCV it decreases by ∼0.7% in the same interval. This means that the compression anisotropy for Ca9R(VO4)7 is of opposite sign in respect to the parent TCV. Within the phosphates of whitlockite-related structure, some are stiffer along the c-axis (tuite and Sr3(PO4)2),24,46 whereas β-Ca3(PO4)2 has been reported to compress isotropically.25 The number of known examples is too low to discuss the possible trends in anisotropy behavior. The XRD experiments were conducted up to about hydrostaticity limit of used PTM (∼10 GPa for methanol− ethanol).47,48 In EOS calculations we used only the data up to ∼9 GPa, to avoid any influence of nonhydrostaticity, which is known to induce unwanted effects on calculated K0.51 In this range no significant broadening of the diffraction peaks was observed, in agreement with the expectations based on results of hydrostatic and nonhydrostatic pressure-transmitting media analysis.47,48 Therefore, the values of bulk moduli obtained in this work can be treated as reliable. For amorphization of orthophosphates, multiple studies have been undertaken (for a review, see ref 52), whereas the number of reported orthovanadates undergoing amorphization is apparently lower. Here, a broadening of diffraction lines is observed for the highest pressures in case of Ca9Nd(VO4)7 crystal. The increase in a peak width could be simply caused by the earlier mentioned nonhydrostaticity of the PTM. On the other hand we observe:

PTM (these features are observed at 8.26(5) GPa during decompression). - An indication of some structural changes noticed by Raman spectroscopy at similar pressures (using argon as PTM, which is quasi-hydrostatic up to ∼15 GPa).48 Together, these give strong arguments for interpreting the observed transition as a pressure-induced amorphization of the crystals ∼10 GPa. An eventual nonhydrostaticity of the chosen PTM can just influence the onset of this transition. The diffractograms for the investigated crystals in this work do not show any significant structural changes at pressures of ∼9 GPa, at which we had observed the very beginning of the transition at Raman spectra (through a significant broadening of the peaks). Probable reason for such inconsistency could be the fact that Raman spectroscopy is more sensitive to any variation in chemical bonding than powder XRDat the onset of the transition some subtle changes in the structure could not be visible on diffractograms. Distinct experimental techniques can be more or less sensitive to the short and long-range order in the crystal, therefore providing not identical description for the amorphization process; some examples regarding such inconsistencies are discussed in ref 53. To better understand the character of pressure-induced changes at Ca9R(VO4)7 crystals, a future extension of XRD studies at higher pressures is necessary. Unpolarized Raman spectra of Ca9R(VO4)7 (R = Y, La, Nd, Gd) crystals at ambient pressure (Figure 7) were found to be similar to those acquired for the parent compound (Ca 3 (VO 4 ) 2 ), 2 1 Tm:Ca 9 La(VO 4 ) 7 , 5 4 Ca 9 Nd(VO 4 ) 7

- A rising-up of the background at ∼7−11° 2θ range. - A large hysteresis of diffraction-peak broadening, extended even below the hydrostaticity limit of the H


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Inorganic Chemistry

Table 2. Modes Observed at Ambient Pressure ν0 [cm−1] and Constants Describing Their Pressure Dependence (up to a Beginning of the Transition) Using Formula νp = νi0 + βp (νi0 and β are Expressed in [cm−1] and [cm−1/GPa], Respectively) for Ca9R(VO4)7 (R = Y, La, Nd, Gd)a R=Y ν0

νi0

R = La β

151b 181 188 203

176 185 213

1.42 2.14 3.86

274 287 306 327 341 352 357 367 390 416 425 434 449 466 715 746 767

274 287 306 326 338 354 360 369 386 412 423 439 453 469 733 754 769

1.72 2.17 1.93 0.93 3.47 4.65 5.53 5.59 4.29 2.66 4.47 2.88 4.52 4.23 4.82 3.10 3.42

799 818 830 853 868 897 904 924 946

796 810 832 856 871 897 907 925 945

2.15 3.70 5.13 6.25 2.63 4.76 4.70 4.39 3.54

R = Nd

ν0

νi0

β

γiT

ν0

93 127 149 162 177 198 236 247 291 321 332 341 356 371 394 434 444

105 124 148 160 179 207 236 250 296 322 333 340 358 370 402 430 444

2.49 2.35 2.24 3.77 3.92 4.29 3.82 2.76 2.25 1.28 2.29 2.83 4.93 5.89 4.07 5.58 6.60

1.494 1.194 0.954 1.484 1.380 1.306 1.020 0.696 0.479 0.250 0.433 0.524 0.868 1.003 0.638 0.818 0.936

157b 188 211 238

νi0 186 210 233

266 285 325 342 351 356 377 397 406 453 467

739 762 785

743 767 785

3.1 3.87 5.3

0.263 0.318 0.425

799 818 831 847 850 854 861 900 919 940

801 817 831 852 862 869 861 899 920 939

3.61 4.16 4.65 5.28 6.69 7.16 3.00 4.60 4.09 3.85

0.284 0.321 0.353 0.390 0.489 0.519 0.220 0.322 0.280 0.258

R = Gd β

γiT

ν0

νi0

β

γiT

131

2.89

1.346

1.59 3.97 2.80

0.539 1.191 0.757

132 154b 199 234

211 236

2.61 0.86

0.755 0.222

267 277 320 338 355 360 378 404 406 450 459

1.79 5.36 2.59 2.75 3.58 4.53 4.50 3.24 7.85 6.16 10.74

0.422 1.219 0.510 0.513 0.635 0.793 0.750 0.505 1.218 0.862 1.474

286 308 323 341 350 356 366 413 433 444 449 480

288 304 324 338 346 358 365 410 431 441 451 475

0.89 0.91 1.21 1.57 1.90 3.22 4.38 2.74 2.38 3.78 4.36 3.54

0.189 0.183 0.228 0.283 0.335 0.549 0.732 0.408 0.337 0.523 0.590 0.455

721 743 764

722 747 767

3.30 2.55 3.27

0.288 0.215 0.269

799 816 832 851 866 926 944

798 818 833 862 863 927 936

2.65 2.25 4.17 6.21 3.00 3.33 4.73

0.209 0.173 0.315 0.454 0.219 0.226 0.318

700 726 745 765 798 815 851 863 867 879 923 950

707 729 744 768 794 804 844 861 869 888 924 946

5.41 4.36 3.77 3.77 2.93 4.70 2.90 5.01 2.31 4.74 3.52 2.31

0.467 0.365 0.309 0.299 0.225 0.357 0.210 0.355 0.162 0.326 0.232 0.149

a Grüneisen parameters γiT for R = La, Nd, and Gd crystals were calculated using isothermal bulk moduli (obtained from third order of EOS) from Table 1. Bolded modes are related to the main peaks in the spectra. bPeaks at ambient pressure that do not change their position during compression. At low-energy part most of the peaks cannot be resolved unambiguously because of the modes overlapping with the signals from Ar.

Figure 10. Raman modes positioning as a function of pressure for Ca9Y(VO4)7 crystal during compression in low- (a) and high- (b) energy range. I


Article

Inorganic Chemistry (polarized spectra),16 and a set of alkali metal-containing TCV-Ca10M(VO4)7 (M = Li, Na, K).38,55 In particular, the main peaks for all these crystals belong to two groups of bands; the widest referred ranges contain wavenumbers ∼50−500 cm−1 and 700−1000 cm−1. Going into more detail, the lines at the low-frequency region are generally attributed to O−V−O bending modes, translational VO4 oscillations, and Ca2+-ions displacements, whereas the high-frequency modes are related to V−O stretching bands and, in case of rare-earth-doped TCV, to the V−O−R chain vibrations (positioned at ∼880−910 cm−1, as reported for the Ca9Nd(VO4)7 crystal).16 The bands at similar energies are typical for other orthovanadates, containing rareearthsa broad review is available at ref 56. The large breadth of the Raman peaks is typical for whitlockite-related calcium vanadates, which is due to occurrence of nonequivalent atomic sites, with cations having different coordination spheres in the Ca-whitlockite structure.38 Opposite shift in Raman peaks with applied pressure is usually attributed to a phase transitionhere observed for Ca9R(VO4)7 at pressures of ∼9−11 GPa. The transition can take place to an amorphous or a new crystalline phase. However, visible broadening and disappearing of the most peaks is analogous to the features observed in Raman spectra of related materials, for which a transition to amorphous phase has been reported. In particular, the amorphization of TCV has been observed at pressure of ∼10 GPa in a combined Raman and XRD study.21 For phosphates of similar structure, such transition has been observed at higher pressures: for β-TCP at 20.8 GPa just based on Raman investigations22 and for magnesium-substituted tricalcium phosphate (β-TMCP), based solely on XRD, at ∼32 GPa.29 These indications of amorphization regarding four calcium orthovanadates at ∼10 GPa coincide with the above-mentioned XRD results for Ca9Nd(VO4)7, where this process starts just above that pressure level. Two possible mechanisms of such phase transition have been briefly discussed, that is, for Ba- and Ca-orthovanadates,57,21 as well as for rare-earth orthovanadates and other AXO4 compounds.56,58

much more rigid than the Ca (or other A cation) coordination polyhedra, in which the A ion undergoes a large displacements during compression.56 The collapse of the Ca-centered polyhedron leads to the loss of translational periodicity.58 As compared to Ca9R(VO4)7, where structural vacancies at the Ca-site are generated by incorporating some rare earths, the described mechanism is expected to be enhanced. To confirm such a mechanism in Ca9R(VO4)7, XRD experiments allowing for refinement of atomic positions are necessary. As TCV can be treated as a parent material for the Ca9R(VO4)7 crystals, we find it advantageous to present here, in more detail, a comparison of high-pressure behavior between these materials, referring to available literature.21 Some experimental issues, such as choice of the sample form (polycrystalline or monocrystalline), wavelength of radiation used (488 or 532 nm) or applied PTM at Raman spectroscopy (CsI or Ar) could influence the resolution and intensity of registered peaks, but some observed discrepancies described below are most likely caused by the presence of rare earth atoms at the Ca sites as well as presence of structural vacancies in the Ca3(VO4)2 structure. First, the amorphization in TCV-based compounds is apparently less sluggish than in the parent material (from 8.1 to 14.8 GPa based on Raman study for TCV),21 close to 4 GPa (evaluated range: R = Y: 8−12 GPa, R = La and Gd: 9−13.5 GPa, R = Nd: 10−13.5 GPa). From all of the investigated compounds, Ca9Y(VO4)7 tends to start the transition at the lowest pressure, which can be caused by the smallest size among all four ions incorporated into Ca sites, making the structure less stable and easier to collapse. The characteristic feature, visible in both TCV and Ca9R(VO4)7, is a negative shift of the high-energy modes (belonging to the frequency range from 700 to 950 cm−1) in the pressure interval where the transition to an amorphous phase takes place. In Ca9R(VO4)7 crystals the low-energy group of modes also exhibits a negative shift, which has not been clearly observed for the TCV.21 Simultaneously with this red shift, the features related to the existence of sixfold coordinated vanadium ions (peak at 600 cm−1 and low-energy shoulder of the main bands ∼750 cm−1)57 are noticed. As compared to the TCV, the visibility of the band around 600 cm−1 is quite pronounced; therefore, we can conclude that the presence of rare earth atoms at Ca sites favors the process of creating highly coordinated V atoms during the amorphization, as compared to the TCV. A large hysteresis of the transition, manifesting itself in a partial return to the initial positions and widths of the peaks of the Raman spectra, indicates a first-order transition for the rare-earth-containing crystals; this is a behavior similar to that of the parent compound.21 However, TCV exhibits quite monotonic widening of the bands, whereas in Ca9R(VO4)7, when analyzing the collected spectra in more detail, even twostage hysteresis can be seen. Down to 3−4 GPa we observed a similar behavior as reported for TCV, but around such pressures we also noticed apparent reduction of the peak width. It is worth pointing out that this pressure interval is the same as the onset of outpacing process between the most intensive Raman modes by adjacent ones from a low-energy side, which was described in the Results Section. One important difference in the behavior of rare-earthcontaining and parent TCV must be noticed: the most intense peaks in Ca9R(VO4)7 spectra exhibit quite low pressure

- The first approach is based on the visible changes in Raman spectra during a phase transition (in particular, amorphization in the TCV case), which indicates a large VO4 units deformation, leading ultimately to the increase of the vanadium ion coordination number from four to sixthis mechanism is supported by the appearance of several bands near 600−620 cm−1 (as predicted, but not observed for TCV)21 and a swift shoulder development in high-frequency bands, near 770 cm−1.57 For all the crystals investigated in this work, we can observe these two features. The described distortion of the vanadium environment has been considered as related to atomic displacements within the Ca-centered polyhedra. However, those changes associated with Ca ions cannot be determined unambiguously, because of weak signal intensity (becoming even weaker during compression) related to the Ba (or Ca) ions, as compared to the lowfrequency V−O modes, which are overlapping with them. The change of vanadium ions coordination has been already found for a few other vanadates and phosphates at high pressure.56 - In the second approach, the VO4 (or generally XO4 tetrahedra in AXO4 compounds) units were found to be J


Article

Inorganic Chemistry coefficients (much lower than an analogous mode observed for TCV), whereas neighboring modes from the lower energies exhibit ∼2 times higher pressure coefficients. We suppose that this behavior is due to the presence of the rare earth dopants, which support translational movements of the VO4 units as compared to the TCV before the amorphization. In the lowenergy region (from 200 to 450 cm−1) we observe a few modes with large pressure coefficients, and therefore large Grüneisen parameters are obtained. In the cited ref 21, such high values have been explained by the Ca displacements and higher compressibility in the c direction, caused by the specific packing of the VO4 units along this crystallographic axis. As for Ca9R(VO4)7 crystals, this anisotropy is opposite, despite their very closely related structures; thus, the probable reason for such high Grüneisen parameter values is the presence of the dopants and structural vacancies at the Ca sites, making the Ca/R polyhedron units less rigid.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Katarzyna M. Kosyl: 0000-0001-6876-1381 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The in situ X-ray diffraction experiments were performed at the BL04-MSPD beamline of the ALBA Synchrotron Facility. This work was partially supported by CALIPSO Project funded by the European Commission under the Seventh Framework Programme (O.E.), European Community in the frame of European Action towards Leading Centre for Innovative Materials (Eagle) REGPOT-2012-2013-1,EU FP7 (R.M. and J.D.), and the Polish National Science Centre (Project No. 2015/17/B/ST5/01658) (D.W. and A.S.). The help of A. Behrooz (Institute of Physics PAS) at the early stages of analysis of ambient-pressure diffraction patterns is gratefully acknowledged.

5. CONCLUSIONS Elastic properties and phase relationships under high pressure for whitlockite-related crystals of Ca9R(VO4)7 formula remained unexplored until now. In the present study such Czochralski-grown crystals were investigated under high pressure by powder X-ray diffraction (for R = La, Nd, Gd) and single-crystal Raman spectroscopy (for R = Y, La, Nd, Gd). We address the elastic and vibrational properties, as well as the amorphization process, of those compounds. The results obtained with X-ray diffraction permitted to determine, for the first time for crystals of the Ca9R(VO4)7 series, the B.-M. EOS; the resulting bulk moduli are K0 = 63(4), 63(2), and 61(5) GPa for R = La, Nd, and Gd, respectively. These values are up to ∼20% lower than that reported for a structurally related vanadate, Ca3(VO4)2. A considerable compressibility anisotropy is observed; the lattice is stiffer in [001] than in [100] direction. The Raman study shows that all the compounds exhibit a sluggish phase transition, most probably to an amorphous phase, with the onset of ∼9−10 GPa. During the transition process, Raman peaks broaden and shift toward low energies. For Ca9Nd(VO4)7, the variation of the diffractograms above 10 GPa provides an additional indication about the beginning of amorphization process; after decompression the whitlockite-like structure is recovered, with hysteresis of at least 3 GPa. On the basis of the case of XRD measurements for Ca9Nd(VO4)7, the transition seems to be fully reversible when the given crystal is decompressed from ∼10 GPa, whereas Raman spectroscopy, for all the investigated compounds, suggests only a partial reversibility when pressures ∼15 GPa and higher were applied. On the basis of the results obtained in this work and those reported in available literature, the pressure-induced amorphization seems to be typical for the compounds such as Ca3(VO4)2 and β-Ca3(PO4)2-related structures, with Ca sites partially occupied by other ions. The obtained results extend the knowledge in the littleexplored field of solid-state science regarding the behavior of whitlockite-related materials under elevated pressures. In particular, finding the amorphization conditions among such orthovanadates indicates a possible direction for future, more detailed studies.

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Lattice parameters of Ca9R(VO4)7 (R = La, Nd, Gd) during compression and decompression (PDF)

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REFERENCES

(1) Jolliff, B. L.; Haskin, L. A.; Colson, R. O.; Wadhwa, M. Partitioning in REE-saturating minerals: Theory, experiment, and modeling of whitlockite, apatite, and evolution of lunar residual magmas. Geochim. Cosmochim. Acta 1993, 57 (16), 4069−4094. (2) Hughes, J. M.; Jolliff, B. L.; Gunter, M. E. The atomic arrangement of merrillite from the Fra Mauro Formation, Apollo 14 lunar mission: The first structure of merrillite from the Moon. Am. Mineral. 2006, 91 (10), 1547−1552. (3) Xie, X.; Minitti, M. E.; Chen, M.; Mao, H. K.; Wang, D.; Shu, J.; Fei, Y. Natural high-pressure polymorph of merrillite in the shock veins of the Suizhou meteorite. Geochim. Cosmochim. Acta 2002, 66 (13), 2439−2444. (4) Adcock, C. T.; Tschauner, O.; Hausrath, E. M.; Udry, A.; Luo, S. N.; Cai, Y.; Ren, M.; Lanzirotti, A.; Newville, M.; Kunz, M.; Lin, C. Shock-transformation of whitlockite to merrillite and the implications for meteoritic phosphate. Nat. Commun. 2017, 8, 14667. (5) Lazoryak, B. I.; Morozov, V. A.; Safonov, M. S.; Khasanov, S. S. Redox reactions in double calcium and iron phosphates. Mater. Res. Bull. 1995, 30 (10), 1269−1275. (6) Belik, A. A.; Morozov, V. A.; Khasanov, S. S.; Lazoryak, B. I. Crystal structures of double vanadates Ca9R(VO4)7: I. R= La, Pr, and Eu. Crystallogr. Rep. 1997, 42 (5), 751−757. (7) Belik, A. A.; Morozov, V. A.; Kotov, R. N.; Khasanov, S. S.; Lazoryak, B. I. Crystal structure of double vanadates Ca9R(VO4)7. II. R= Tb, Dy, Ho, and Y. Crystallogr. Rep. 2000, 45 (3), 389−394. (8) Belik, A. A.; Morozov, V. A.; Grechkin, S. V.; Khasanov, S. S.; Lazoryak, B. I. Crystal structures of double vanadates, Ca9R(VO4)7· III. R= Nd, Sm, Gd, or Ce. Crystallogr. Rep. 2000, 45 (5), 728−733. (9) Belik, A. A.; Grechkin, S. V.; Dmitrienko, L. O.; Morozov, V. A.; Lazoryak, B. I.; Khasanov, S. S. Crystal Structures of Double Vanadates Ca9R(VO4)7. IV. R= Er, Tm, Yb, and Lu. Crystallogr. Rep. 2000, 45 (6), 896−901. (10) Belik, A. A.; Yanov, O. V.; Lazoryak, B. I. Synthesis and crystal structure of Ca9Cu1.5(PO4)7 and reinvestigation of Ca9.5Cu(PO4)7. Mater. Res. Bull. 2001, 36 (10), 1863−1871. (11) El Khouri, A.; Elaatmani, M.; Della Ventura, G.; Sodo, A.; Rizzi, R.; Rossi, M.; Capitelli, F. Synthesis, structure refinement and vibrational spectroscopy of new rare-earth tricalcium phosphates

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S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b01182. K


Article

Inorganic Chemistry Ca9RE(PO4)7 (RE= La, Pr, Nd, Eu, Gd, Dy, Tm, Yb). Ceram. Int. 2007, 43 (17), 15645−15653. (12) Piccinelli, F.; Trevisani, M.; Plaisier, J. R.; Bettinelli, M. Structural study of Yb3+, Eu3+ and Pr3+ doped Ca9Lu(PO4)7. J. Rare Earths. 2015, 33 (9), 977−982. (13) Guo, N.; You, H.; Song, Y.; Yang, M.; Liu, K.; Zheng, Y.; Huang, Y.; Zhang, H. White-light emission from a single-emittingcomponent Ca9Gd(PO4)7: Eu2+, Mn2+ phosphor with tunable luminescent properties for near-UV light-emitting diodes. J. Mater. Chem. 2010, 20 (41), 9061−9067. (14) Li, L.; Noh, H. M.; Moon, B. K.; Jeong, J. H.; Choi, B. C.; Liu, X. Tunable white-light emission in single-phase Ca9Gd(VO4)7:Tm3+, Eu3+. Opt. Mater. Express 2014, 4 (1), 16−28. (15) Zhang, Y. J.; Mao, Z. Y.; Wang, D. J.; Zhao, J. Synchronous red and blue emitting Ca3(PO4)2: Eu2+, Mn2+ phosphors applicable for plant-lighting. Mater. Res. Bull. 2015, 67, 1−4. (16) Demesh, M. P.; Yasukevich, A. S.; Kuleshov, N. V.; Kosmyna, M. B.; Mateychenko, P. V.; Nazarenko, B. P.; Shekhovtsov, A. N.; Kornienko, A. A.; Dunina, E. B.; Orlovich, V. A.; Khodasevich, I. A.; Paszkowicz, W.; Behrooz, A. Growth and spectroscopic properties of Ca9Nd(VO4)7 single crystal. Opt. Mater. 2016, 60, 387−393. (17) Calvo, C.; Gopal, R. The crystal structure of whitlockite from the Palermo Quarry. Am. Mineral. 1975, 60 (1−2), 120−133. (18) Sleight, A. W.; Huang, J. U.S. Patent No. 5,202,891. U.S. Patent and Trademark Office: Washington, DC, 1993. (19) Bechthold, P. S.; Liebertz, J.; Deserno, U. Linear and nonlinear optical properties of Ca3(VO4)2. Opt. Commun. 1978, 27 (3), 393− 398. (20) Paszkowicz, W.; Shekhovtsov, A.; Kosmyna, M.; Loiko, P.; Vilejshikova, E.; Minikayev, R.; Romanowski, P.; Wierzchowski, W.; Wieteska, K.; Paulmann, C.; Bryleva, E.; Belikov, K.; Fitch, A. Structure and thermal expansion of Ca9Gd(VO4)7: A combined powder-diffraction and dilatometric study of a Czochralski-grown crystal. Nucl. Instrum. Methods Phys. Res., Sect. B 2017, 411, 100−111. (21) Grzechnik, A. Amorphization of Ca3(VO4)2 at High Pressure. J. Solid State Chem. 1998, 139 (1), 161−167. (22) Shakhvorostov, D.; Müser, M. H.; Mosey, N. J.; MunozPaniagua, D. J.; Pereira, G.; Song, Y.; Kasrai, M.; Norton, P. R. On the pressure-induced loss of crystallinity in orthophosphates of zinc and calcium. J. Chem. Phys. 2008, 128 (7), 074706. (23) Shakhvorostov, D.; Müser, M. H.; Mosey, N. J.; Song, Y.; Norton, P. R. Correlating cation coordination, stiffness, phase transition pressures, and smart materials behavior in metal phosphates. Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 79 (9), 094107. (24) Zhai, S.; Liu, X.; Shieh, S. R.; Zhang, L.; Ito, E. Equation of state of γ-tricalcium phosphate, γ-Ca3(PO4)2, to lower mantle pressures. Am. Mineral. 2009, 94 (10), 1388−1391. (25) Zhai, S.; Wu, X. X-ray diffraction study of β-Ca3(PO4)2 at high pressure. Solid State Commun. 2010, 150 (9-10), 443−445. (26) Zhai, S.; Wu, X.; Ito, E. High-pressure Raman spectra of tuite, γ-Ca3(PO4)2. J. Raman Spectrosc. 2010, 41 (9), 1011−1013. (27) Liang, L.; Rulis, P.; Ching, W. Y. Mechanical properties, electronic structure and bonding of α- and β-tricalcium phosphates with surface characterization. Acta Biomater. 2010, 6 (9), 3763−3771. (28) Zhai, S.; Wu, X.; Xue, W. Pressure-dependent Raman spectra of β-Ca3(PO4)2 whitlockite. Phys. Chem. Miner. 2015, 42 (4), 303−308. (29) Scott, P. R.; Crow, J. A.; LeGeros, R. Z.; Kruger, M. B. A pressure-induced amorphous phase transition in magnesium-substituted β-tricalcium phosphate. Solid State Commun. 2011, 151 (21), 1609−1611. (30) Brunet, F.; Allan, D. R.; Redfern, S. A.; Angel, R. J.; Miletich, R.; Reichmann, H. J.; Sergent, J.; Hanfland, M. Compressibility and thermal expansivity of synthetic apatites, Ca5(PO4)3X with X = OH, F and Cl. Eur. J. Mineral. 1999, 11 (6), 1023−1035. (31) Murayama, J. K.; Nakai, S.; Kato, M.; Kumazawa, M. A dense polymorph of Ca3(PO4)2: a high pressure phase of apatite decomposition and its geochemical significance. Phys. Earth Planet. Inter. 1986, 44 (4), 293−303.

(32) Sugiyama, K.; Tokonami, M. Structure and crystal chemistry of a dense polymorph of tricalcium phosphate Ca3(PO4)2: A host to accommodate large lithophile elements in the earth’s mantle. Phys. Chem. Miner. 1987, 15 (2), 125−130. (33) Thompson, R. M.; Xie, X.; Zhai, S.; Downs, R. T.; Yang, H. A comparison of the Ca3(PO4)2 and CaSiO3 systems, with a new structure refinement of tuite synthesized at 15 GPa and 1300°C. Am. Mineral. 2013, 98 (8−9), 1585−1592. (34) Xie, X.; Zhai, S.; Chen, M.; Yang, H. Tuite, γ-Ca3(PO4)2, formed by chlorapatite decomposition in a shock vein of the Suizhou L6 chondrite. Meteorit. Planet. Sci. 2013, 48 (8), 1515−1523. (35) Grzechnik, A. Crystal structure of Ca3(VO4)2 synthesized at 11 GPa and 1373 K. Solid State Sci. 2002, 4 (4), 523−527. (36) Kovyazina, S. A.; Perelyaeva, L. A.; Leonidova, O. N.; Leonidov, I. A.; Ivanovskii, A. L. High-temperature Raman spectroscopy and phase transformations in phosphates and vanadates Ca3−3xNd2x(AO4)2 (A = P, V; 0≤ x≤ 0.14). Crystallogr. Rep. 2004, 49 (2), 211−214. (37) Pogosova, M. A.; Azarmi, F.; Eliseev, A. A.; Kazin, P. E. Eu and Cu co-substituted calcium vanadateThe crystal structure, luminescence and color. Dyes Pigm. 2018, 148, 219−223. (38) Khodasevich, I. A.; Voitikov, S. V.; Orlovich, V. A.; Kosmyna, M. B.; Shekhovtsov, A. N. Raman spectra of crystalline double calcium orthovanadates Ca10M(VO4)7 (M= Li, K, Na) and their interpretation based on deconvolution into Voigt profiles. J. Appl. Spectrosc. 2016, 83 (4), 555−561. (39) Dobrotvorskaya, M. V.; Gorobets, Y. N.; Kosmyna, M. B.; Mateichenko, P. V.; Nazarenko, B. P.; Puzikov, V. M.; Shekhovtsov, A. N. Growth and Characterization of Ca9Ln(VO4)7 Crystals (Ln = Y, La, or Gd). Crystallogr. Rep. 2012, 57 (7), 959−961. (40) Fauth, F.; Peral, I.; Popescu, C.; Knapp, M. The new material science powder diffraction beamline at ALBA synchrotron. Powder Diffr. 2013, 28 (S2), S360−S370. (41) Boehler, R. New diamond cell for single-crystal X-ray diffraction. Rev. Sci. Instrum. 2006, 77 (11), 115103. (42) Hammersley, A. P. FIT2D: a multi-purpose data reduction, analysis and visualization program. J. Appl. Crystallogr. 2016, 49 (2), 646−652. (43) Rodríguez-Carvajal, J. Recent advances in magnetic structure determination by neutron powder diffraction. Phys. B 1993, 192 (1− 2), 55−69. (44) Angel, R. J.; Alvaro, M.; Gonzalez-Platas, J. EosFit7c and a Fortran module (library) for equation of state calculations. Z. Kristallogr. - Cryst. Mater. 2014, 229 (5), 405−419. (45) Angel, R. J.; Wood, I. G. Fitting equations of state. IUCr Newsletter of the Commission on Crystallographic Computing 2003, 1, 72−75. (46) Zhai, S.; Xue, W.; Yamazaki, D.; Shan, S.; Ito, E.; Tomioka, N.; Shimojuku, A.; Funakoshi, K. I. Compressibility of strontium orthophosphate Sr3(PO4)2 at high pressure. Phys. Chem. Miner. 2011, 38 (5), 357−361. (47) Angel, R. J.; Bujak, M.; Zhao, J.; Gatta, G. D.; Jacobsen, S. D. Effective hydrostatic limits of pressure media for high-pressure crystallographic studies. J. Appl. Crystallogr. 2007, 40 (1), 26−32. (48) Klotz, S.; Chervin, J. C.; Munsch, P.; Le Marchand, G. Hydrostatic limits of 11 pressure transmitting media. J. Phys. D: Appl. Phys. 2009, 42 (7), 075413. (49) Anderson, D. L.; Anderson, O. L. The Bulk Modulus-Volume Relationship for Oxides. J. Geophys. Res. 1970, 75 (17), 3494−3500. (50) Errandonea, D.; Lacomba-Perales, R.; Ruiz-Fuertes, J.; Segura, A.; Achary, S. N.; Tyagi, A. K. High-pressure structural investigation of several zircon-type orthovanadates. Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 79 (18), 184104. (51) Errandonea, D.; Muñoz, A.; Gonzalez-Platas, J. Comment on “High-pressure x-ray diffraction study of YBO3/Eu3+, GdBO3, and EuBO3: Pressure-induced amorphization in GdBO3” [J. Appl. Phys. 115, 043507(2014)]. J. Appl. Phys. 2014, 115, 216101. (52) Dorozhkin, S. V. Amorphous calcium (ortho) phosphates. Acta Biomater. 2010, 6 (12), 4457−4475. L


Article

Inorganic Chemistry (53) Sharma, S. M.; Sikka, S. K. Pressure induced amorphization of materials. Prog. Mater. Sci. 1996, 40 (1), 1−77. (54) Zhang, Z.; Loiko, P.; Wu, H.; Mateos, X.; Serres, J. M.; Lin, H. F.; Chen, W. D.; Zhang, G.; Zhang, L. Z.; Díaz, F.; Aguiló, M.; Petrov, V.; Griebner, U.; Wang, Y. C.; Vilejshikova, E.; Yumashev, K.; Lin, Z. B. Disordered Tm: Ca9La(VO4)7: a novel crystal with potential for broadband tunable lasing. Opt. Mater. Express 2017, 7 (2), 484−493. (55) Popov, P. A.; Skrobov, S. A.; Matovnikov, A. V.; Kosmyna, M. B.; Puzikov, V. M.; Nazarenko, B. P.; Shekhovtsov, A. N.; Behrooz, A.; Paszkowicz, W.; Khodasevich, I. A.; Shereshovets, N. N.; Voitikov, S. V.; Orlovich, V. A. Thermal Conductivity Investigation of Ca9RE(VO4)7 (RE = La, Nd, Gd) and Ca10M(VO4)7 (M = Li, Na, K) Single Crystals. Int. J. Thermophys. 2017, 38 (1), 10. (56) Errandonea, D.; Garg, A. B. Recent progress on the characterization of the high-pressure behaviour of AVO4 orthovanadates. Prog. Mater. Sci. 2018, 97 (8), 123−169. (57) Grzechnik, A.; McMillan, P. F. In situ high pressure Raman spectra of Ba3(VO4)2. Solid State Commun. 1997, 102 (8), 569−574. (58) Errandonea, D.; Somayazulu, M.; Häusermann, D. Phase transitions and amorphization of CaWO4 at high pressure. Phys. Status Solidi B 2003, 235 (1), 162−169.

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