Article pubs.acs.org/crystal
Continuous Flow Supercritical Water Synthesis and TemperatureDependent Defect Structure Analysis of YAG and YbAG Nanoparticles Peter Nørby,† Kirsten M. Ø. Jensen,‡ Nina Lock,§ Mogens Christensen,† and Bo B. Iversen*,† †
Department of Chemistry and iNANO, Center for Materials Crystallography, Langelandsgade 140, DK-8000 Aarhus C, Denmark Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 København Ø, Denmark § iNANO and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark ‡
S Supporting Information *
ABSTRACT: Yttrium and ytterbium aluminum garnet (Y3Al5O12 and Yb3Al5O12) nanoparticles have been synthesized under sub- and supercritical water conditions in a continuous flow reactor. The particle size has been investigated by scanning and transmission electron microscopy. The heat-induced structural changes of the garnet structure have been investigated by multitemperature powder X-ray diffraction at a synchrotron source (100−1000 K). In combination, Rietveld refinement of these multitemperature data and thermal analysis indicate a proposed diffusion mechanism for the aluminum and yttrium/ytterbium atoms in the garnet structure, which leads to fewer defects at higher temperature. Hence, hydrothermally synthesized nanoparticles give novel knowledge about the disordered internal structure important for their use in optical applications.
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INTRODUCTION The garnets of yttrium aluminum (Y3Al5O12, YAG) and ytterbium aluminum (Yb3Al5O12, YbAG) have many applications, e.g., as thermal barrier coatings, erosion resistant materials, and in particular in solid-state lasers.1−3 Trivalent rare-earth doped YAG compounds are mainly used in solidstate laser materials in single-crystalline form1 but more recently also in polycrystalline form.4 The performance of lasers based on polycrystalline material strongly depends on the particle size, size distribution, morphology, and structural defects. For ideal optical performance, spherical nanoparticles with a narrow size distribution are preferred.5 It is important that the crystal structure is completely free of disorder, as the laser properties can be severely reduced by structural imperfections.4 Garnets have conventionally been synthesized by a solid-state reaction between the oxides of aluminum and yttrium/ ytterbium, where the synthesis takes place at high temperature for hours (1600−1800 °C for 10−20 h).6,7 More refined synthetic routes under milder conditions have now been developed, i.e., coprecipitation methods,5,8 sol−gel methods,2,9,10 and hydrothermal supercritical synthesis methods.7,11−19 The coprecipitation and sol−gel methods require organic reagents and solvents. In contrast, the hydrothermal supercritical approach uses simple inorganic salts as reactants and water as solvent; i.e., it is both cheap and environmentally friendly. The dielectric constant and density of water are dramatically reduced near the critical point (374 °C, 221 bar), making the properties of water under supercritical conditions comparable to those of organic solvents.20−23 Thus, when aqueous solutions under pressure are heated rapidly from room © XXXX American Chemical Society
temperature above the critical point, the ions will instantaneously precipitate as oxides owing to supersaturation, and nanoparticles with a narrow size distribution will form.24,25 Supercritical hydrothermal synthesis can be carried out using either batch or continuous flow reactors, and YAG particles have been synthesized using both of these approaches.12,15 Yoon et al. have compared europium-doped YAG (YAG:Eu) synthesized under hydrothermal supercritical conditions in a batch and a continuous reactor.15 Their study indicates that the continuous synthesis is superior to a batch-type method when it comes to control of size of the resulting YAG particles. The continuous hydrothermal synthesis method yielded phase pure YAG with high crystallinity, and no postsynthesis treatment was needed. Moreover, the obtained nanoparticles were small due to the short reaction time. This technique is thus promising for the synthesis of nanoparticles suitable for ceramic laser applications, for which control of size, morphology, crystallinity, and purity is crucial. The garnet structure crystallizes in the space group Ia3̅d and can be described with the general formula X3Y2Z3O12, where X is the coordinated to eight oxygen atoms and has the Wyckoff notation 24c, while Y is octahedrally coordinated (position 16a) and Z is tetrahedrally coordinated (position 24d). The large ion Y3+ and Yb3+ primarily occupies the 24c site, while Al3+ dominates the 16a and 24d sites. In this study, nanoparticles of YAG and YbAG have been successfully synthesized under continuous flow in sub- and Received: December 13, 2015 Revised: March 27, 2016
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DOI: 10.1021/acs.cgd.5b01761 Cryst. Growth Des. XXXX, XXX, XXX−XXX
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Supporting Information. The defect models are described in the Results. The as-synthesized samples were furthermore investigated by scanning transmission electron microscopy (STEM) and scanning electron microscopy (SEM). For SEM measurements, the nanoparticles were immobilized on conductive carbon tape, and pictures were acquired on a FEI-Nova NanoSEM 600. The STEM samples were prepared by placing a droplet of a small amount of powder suspended in ethanol on a carbon-coated copper grid. The STEM pictures were acquired with a FEI Talos equipped with four energy dispersive X-ray spectroscopy (EDS) detectors by using an acceleration voltage of 200 keV. Thermogravimetric analysis (TG) and differential thermal analysis (DTA) were performed simultaneously on a Jupiter NETZSCH STA 449 C thermal analyzer. A small amount of the nanoparticles were placed in an open Al2O3 crucible, which was subsequently heated from 298 to 1000 K with a heating rate of 3.9 K/min and cooled at a rate of 5 K/min. The heating rate imitates the conditions under which the multitemperature PXRD data were collected. Both the YAG and YbAG samples have been measured in both a 100% He (inert) atmosphere and in an atmosphere consisting of 80% He and 20% O2 (referred to as 20% O2).
supercritical water from a metal nitrate aqueous solution (T = 350−450 °C, p = 300 bar). The effects of synthesis temperature on the morphology and size of the as-synthesized nanoparticles are presented. Detailed structural analyses are often neglected in characterization of nanoparticles, although it is of utmost importance for the optical properties. Therefore, multitemperature synchrotron powder X-ray diffraction (PXRD) patterns were collected to study the temperature-dependent defect structure of the garnets. Rietveld refinement of the data reveals a complex defect structure which changes as a function of temperature. Furthermore, the weight loss during annealing has been investigated by thermal analysis, and the particle size and morphology after heating have been compared with the asprepared nanoparticles.
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EXPERIMENTAL SECTION
The following reagents were used as purchased: Al(NO3)3·9H2O (ACS reagent), Y(NO3)3·6H2O (99.8%), Yb(NO3)3·5H2O (99.9%), and KOH. Precursor solutions were made by dissolving the metal nitrates of aluminum, yttrium, and ytterbium in deionized water. In the synthesis of YAG/YbAG the aluminum nitrate (0.842/0.490 M) and yttrium/ytterbium nitrate (0.505/0.294 M) solutions were mixed. The pH was adjusted to approximately 9 by dropwise addition of an aqueous 4 M KOH solution. This resulted in a white gelatinous solution, which was centrifuged and washed repeatedly until neutral pH of the supernatant was obtained. The precipitate was subsequently suspended in deionized water. A custom-made continuous flow reactor with a heated reaction chamber of 7.3 mL was used to produce YAG and YbAG from the suspended precipitate (reactant). The reactor setup is similar to that described by Adschiri et al. and that used by Becker et al.26,27 All experiments were done at 300 bar and with the solvent preheater and main solvent heater set to 350 and 475 °C, respectively. The temperature of the reaction chamber was varied: In the synthesis of YAG, four different reaction chamber temperatures were applied (300, 350, 400, and 450 °C) and in YbAG two temperatures (400 and 450 °C). The solvent and reactant pumps were both set to a flow rate of 10 mL/min, and the reactant was stirred throughout the synthesis to ensure homogeneity. The product was centrifuged and subsequently dried at room temperature. PXRD patterns of the obtained nanoparticles were recorded at beamline BL44B2, SPring-8 (Harima, Japan) in a multitemperature setup. The samples were prepared by packing the nanoparticles into quartz capillaries (inner diameter 0.1 mm). The wavelength was 0.499 Å. The temperature was controlled with a hot air blower, and the PXRD data were collected on image plates mounted in a Debye− Scherrer camera covering an angular 2θ-range of 2−77°. All PXRD data are presented in the Q-range (Q = (4π sin θ)/λ) 0.44−15.6 Å−1. For the samples synthesized at 400 °C, PXRD patterns were collected at temperatures from 100 to 1000 K, and an additional pattern was recorded after cooling to 315 K. Samples synthesized at 300 °C, 350 °C, and 450 °C were only studied at 315 K. Rietveld refinement of the data was done in the FullProf Suite program package28 describing the peak profile by a Thompson-Cox-Hastings (TCH) pseudo-Voigt function with axial divergence asymmetry.29 The Bragg peak profile is a convolution of contributions from the instrument and the sample. The instrumental contribution was accounted for by measuring data on a microcrystalline CeO2 standard, allowing extracting of the sample contribution from the pattern. The deconvolution of the instrumental and sample-dependent contribution to the broadening was performed in FullProf by including an instrumental resolution file (IRF) in the Rietveld refinements. The scale factor, lattice parameter, Lorentzian shape parameter (X), Gaussian shape parameter (IG), and zero point were refined. The positions of the oxygen atoms were constrained to the coordinates from the Inorganic Crystal Structure Database (ICSD no. 01-073-3186 and no. 01-070-7794).30,31 Furthermore, the atomic displacement parameters (B-values) and partial cation occupancies related to the defect structure were refined, as discussed in detail in the
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RESULTS AND DISCUSSION Phase Identification, Size, and Morphology. The PXRD data of the as-synthesized samples from SPring-8 shown in Figure 1 reveal that YAG and YbAG can be prepared
Figure 1. PXRD patterns of the as-synthesized YAG and YbAG nanoparticles prepared at different temperatures. All the patterns are measured at 315 K at SPring-8. Black asterisks: Garnet phase. Red hash marks: unidentified phase.
hydrothermally in the whole temperature range from 300 to 450 °C. YbAG can be synthesized phase pure, while an unidentified phase coexists with YAG, clearly indicated by an additional double peak around Q = 1.65 Å−1. Smaller peaks are also visible at both sides of the largest peak in the garnet phase (2.3 Å−1). Previous studies have indicated that the synthesis is highly pH and reaction time-dependent, resulting in a range of impurity phases (YOOH, AlOOH, Y4Al2O9, and YAlO3).12,14 The unidentified phase cannot be indexed to any of these impurities phases or other phases by database search. We have recently investigated the crystallite size dependency on synthesis temperature and time of YAG and YbAG nanoparticles in sub- and supercritical water, showing that phase pure YAG and YbAG can only be synthesized at supercritical conditions in a batch reactor.32 B
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Figure 2. Bright-field TEM and STEM pictures of YbAG nanoparticles synthesized at 400 °C. It can be seen by STEM that the nanoparticles are porous. The TEM overview picture reveals that majority of the nanoparticle aggregates are all smaller than 100 nm.
Temperature-Dependent Defect Structure Analysis of YbAG Nanoparticles. Multitemperature PXRD patterns were collected between 100 and 1000 K on the as-synthesized nanoparticles of YbAG and YAG. The PXRD patterns at selected temperatures are shown in Figure 4 and in the
In the following, the focus will be on YbAG synthesized at 400 °C, while similar results are obtained for YAG as shown in Supporting Information. The morphology and size of the assynthesized YbAG nanoparticles prepared at 400 °C were investigated by TEM and STEM measurements as shown in Figure 2. Supporting Information reveal that the particle morphology is spherical, irrespective of the synthesis temperature. This is in agreement with the results obtained by In et al. in the synthesis of Eu-doped YAG.14 The particle size observed is around 70 nm. However, the STEM pictures reveal that the particles observed in the TEM image in fact have a porous structural appearance and are aggregates consisting of several nanoparticles. In the Supporting Information TEM pictures for both YbAG and YAG are shown together with STEM pictures of YAG, indicating a similar porosity for YAG as for YbAG. Figure 3 shows the spatial elemental distributions of oxygen, aluminum, and ytterbium in the nanoparticles. It can be seen from the elemental mapping that the nanoparticles are homogeneous in composition, albeit the porosity of the nanoparticles. Elemental mapping of the YAG particles can be found in the Supporting Information.
Figure 4. Multitemperature PXRD patterns for YbAG obtained at SPring-8 at selected temperatures. Cooled sample refers to the PXRD pattern obtained at room temperature after the sample has been heated to 1000 K.
Supporting Information. In the case of YAG the unidentified phase shown in Figure 1 undergoes a transition in the temperature range 415−465 K. The new unknown phase disappears at 665 K and a phase pure YAG sample is obtained. Hence, impurities have been annealed out of the sample and none of the impurity phases reappear after cooling down the sample from 1000 K to room temperature, see Figure S8 in Supporting Information. For YbAG the PXRD patterns show only one phase throughout the temperature scan as seen in Figure 4. Physical quantities such as lattice parameter, atomic displacement parameters and occupancy are extracted from Rietveld refinement of the high resolution multitemperature data. Figure 5 shows the refined lattice parameter for the YbAG and YAG samples as a function of temperature. Both curves display an unexpected behavior with a deviation from linearity in the
Figure 3. High-angle annular dark field (HAADF) STEM image of YbAG nanoparticles synthesized at 400 °C. The elemental mapping shows that the elements oxygen, aluminum, and ytterbium are distributed uniformly in the particles. C
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Figure 5. Extracted refined lattice parameters for YAG and YbAG as a function of temperature. It can be seen that there is a deviation from linearity in the temperature region 550−850 K. The unknown phase in YAG does not influence the lattice parameter. The open symbols indicate the cooled sample. Estimated standard deviations are smaller than the size of the symbols.
region 565−850 K. The decrease in lattice parameter (negative thermal expansion) is very surprising. The fact that the trend is seen for both samples suggests that the behavior is material related and not caused by experimental artifacts or systematic errors. Furthermore, the impurity present in the YAG sample can be excluded from influencing the thermal expansion as YbAG is completely phase pure. One way to explain the unusual lattice expansion is to look at the internal changes within the unit cell as a function of temperature. In order to describe all the different features in the PXRD patterns two different internal defect mechanisms have to be taken into account. The first one is a cation antisite reaction between the rare-earth metal and one of the aluminum sites, described by the following equation:
Figure 6. Rietveld refinement plots for YbAG at selected temperatures. R-values: 100 K (RBragg = 3.66%, RF = 2.23%), 415 K (RBragg = 3.48%, RF = 3.01%) and 1000 K (RBragg = 2.03%, RF = 4.17%).
pronounced. Figure 7 reveals that the structure of YbAG at 100 K is oxygen deficient and has the general formula: (Yb2.92Al0.08)24c(Al2.19)24d(Al1.92Yb0.08)16aO10.78; the previous listed constraints ensure the necessary boundaries to avoid 100% correlation between occupancies and scale factor. The cation antisite defect mechanism does not play any significant role at this low temperature. Increasing the temperature to 515 K does not change the stoichiometry of the structure, and the general sum formula for YbAG at 515 K is (Yb2.92Al0.08)24c(Al2.17)24d(Al1.92Yb0.08)16aO10.75. Hence, the lattice expansion observed in this temperature range (see Figure 5) can be ascribed to the increased thermal motion of the atoms, which also increases linearly as seen for the ADPs in Figure 7. From 515 to 765 K the lattice of YbAG shows negative thermal expansion, which is the same temperature region where the vacancy formation mechanism is reversed and the structure becomes closer to stoichiometric YbAG. The general formula at 765 K is (Yb2.84Al0.16)24c(Al2.64)24d(Al1.84Yb0.16)16aO11.46. The oxygen and corresponding aluminum atoms might come from nanosized amorphous domains in the nanoparticles or from a surrounding amorphous shell. This is likely the case as the nanoparticles are very porous and have a large surface area, hence large amorphous content, as seen in Figure 2. The ADP for the Al24d in the temperature range 515−765 K is decreasing. Hence, the aluminum atoms become more ordered in the unit cell, which will lead to a reduction of the ADP for Al24d. This might also explain the large ADPs for Al24d found at low temperature as originating from static disorder in the structure. From 765 to 1000 K, the cation antisite defect mechanism influences the structure the most, and at 1000 K the general formula for the YbAG nanoparticles is (Yb2.75Al0.25)24c(Al2.86)24d(Al1.75Yb0.25)16aO11.79. At this temperature, 12.5% of the aluminum atoms from the octahedral sites have diffused to the larger Yb site and vice versa for Yb. Furthermore, the structure is more or less annealed to ideal oxygen content. The thermal motion (ADP) of the 16a site decreases as more
Yb XYb + (AlXAl )16a ⇌ (YbXAl )16a + AlXYb
Previous studies have shown that this is the most energetically favorable intrinsic defect in garnet structures.33 Second, a vacancy formation mechanism was considered, where one aluminum atom is removed for every 3/2 oxygen atom to ensure charge neutrality in the nanoparticle: 3 ·· ‴ + Yb3Al3 − yAl 2O12 − 3/2y ⇌ Yb3Al5O12 y V + yV Al 2 O Combining the two mechanisms yield the following total structural formula: (Yb3 − x Al x)24c (Al3 − y)24d (Al 2 − xYbx )16a O12 − 3/2y
where x and y indicate the degree of antisite defect and vacancy defect, respectively. Figure 6 shows the Rietveld refinement fits obtained on YbAG nanoparticles with R-values listed in the figure caption. There is a very good agreement between model and data when these two defect mechanisms are taken into account. The majority of the fits have R-values in the range of 2−3% as seen in Supporting Information (Figure S9) for the other temperatures. The extracted atomic displacement parameters (ADPs) and occupancies from the Rietveld refinements incorporating these two defect mechanisms are shown in Figure 7. The impurity in the YAG sample might influence the details drawn from the internal structural changes, i.e., ADPs and occupancies, due to partial peak overlap. Hence, YbAG will be used in the following analysis owing to its purity, and YAG data should only be seen as supportive as the same trend is seen, although not as D
DOI: 10.1021/acs.cgd.5b01761 Cryst. Growth Des. XXXX, XXX, XXX−XXX
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Figure 7. Extracted occupancies and ADPs for YbAG and YAG as functions of temperature, where the occupancy is expressed as number of atoms per formula unit. The occupancy of AlYb is equivalent to YbAl.
ytterbium diffuses toward the site. Overall the same trend is seen for YAG, although the temperature onsets of the different mechanisms are at slightly lower temperatures. Cooling the sample to room temperature results in the general formula for YbAG: (Yb 2.75 Al 0.25 ) 24c (Al 2.82 ) 24d (Al1.75Yb0.25)16aO11.73. This shows that the sample is annealed and the overall structure contains cation antisite defects. Hence, in order to get closer to the ideal oxygen content and to be useful in laser material the sample has to be annealed, albeit the antisite defects will also affect the optical properties. It can be concluded that multitemperature PXRD Rietveld analysis of hydrothermally synthesized nanoparticles gives insight into fundamental defect processes present in nanoparticles. Even though the defect analysis is for the garnet phase nanoparticles, similar defects are often found in hydrothermally synthesized nanoparticles, e.g., LiFePO4.34 It can be concluded that the internal atomic structure should be considered when assynthesized hydrothermally synthesized nanoparticles are used in applications. Furthermore, it should be noted that the analysis made here should only be considered as one possible explanation for the unexpected behavior of the lattice parameter. Thermal Analysis of YAG and YbAG. Figure 8 shows the TG and DTA curves for as-synthesized YAG and YbAG nanoparticles in both inert and 20% O2 atmospheres. The two samples show similar trends, although the relative mass loss is larger for YAG than for YbAG. The TG curves (left part of Figure 8) for both YAG and YbAG show a steep mass loss at 490 and 520 K, respectively. This is the temperature where the lattice parameter starts to behave abnormally. A slower mass loss follows starting at approximately 800 K. In the DTA curves (right part of Figure 8) there are common exothermic peaks just above room temperature, corresponding to the evaporation of surface bound water. The DTA curves for YAG and YbAG have a local maximum at elevated temperature, around 720− 770 K and 860−930 K, respectively, depending on the atmosphere. These temperatures correspond reasonable well to the temperatures at which the lattice parameter begins to behave normally, i.e., to increase linearly with temperature; see Figure 5. Hence, the weight loss and thermal events seem to be related to the defect mechanism described in the previous
Figure 8. TG (left) and DTA (right) curves for the YAG and YbAG nanoparticles synthesized at 400 °C. The red dotted lines for the samples heated in 20% O2 and the blue solid lines for the samples heated in inert atmosphere. The heating rates are 3.9 K/min for all experiments. The two vertical dotted lines mark when the unknown phases disappear in YAG.
section. The weight loss might be ascribed to diffusion of aluminum ions from amorphous parts into the crystal structure where the rest of the amorphous part could be volatile species such as water. SEM pictures of the samples after heating in inert and 20% O2 atmospheres, respectively, are shown in Figure 9. The YAG sample heated in inert atmosphere contains needles with lengths of several micrometers in addition to nanoparticles. The only morphology found in YAG heated in a 20% O 2 atmosphere is spherical nanoparticles. It is unclear why this morphology change is observed under inert conditions. In the YbAG samples the morphology remains the same regardless of the heating atmosphere. Although the morphology of the YAG sample heated in different atmospheres differs, the PXRD patterns collected are similar after heating as seen in the insets. The PXRD patterns for YbAG show that the garnet phase is the only crystalline phase present before and after heating. The size obtained from SEM pictures of the nanoparticles after heating to 1000 K reveal that they have not grown significantly, regardless of the heating atmosphere. This supports the idea E
DOI: 10.1021/acs.cgd.5b01761 Cryst. Growth Des. XXXX, XXX, XXX−XXX
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Figure 9. SEM pictures of YAG and YbAG nanoparticles synthesized at 400 °C after TGA measurements to 1000 K: (a) YAG before TGA, (b) YAG heated in 80% He/20% O2 atmosphere, (c) YAG heated in 100% He atmosphere, (d) YbAG before TGA, (e) YbAG heated in 80% He/20% O2 atmosphere, (c) YbAG heated in 100% He atmosphere. The insets are PXRD patterns (Q-range: 0.5−5 Å−1) of the nanoparticles after each treatment, where the hash mark indicates the unidentified phase. The scale bar is 200 nm.
by heating to 1000 K. The study has given us new insight in defects present in hydrothermally synthesized garnet nanoparticles, allowing us to optimize the synthesis parameters in future syntheses. The large defect concentrations limit the direct use of hydrothermally as-synthesized nanoparticles in optical applications.
that condensation of the nanoparticles has happened during annealing.
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CONCLUSION YAG and YbAG nanoparticles with a particle size below 100 nm have been synthesized under sub- and supercritical water conditions in a continuous flow reactor. It was found by STEM that the as-synthesized nanoparticles aggregate into larger porous particles with spherical morphology. Furthermore, it was shown by elemental mapping that they have uniform spatial distribution of the elements. The PXRD data show that in the YAG sample, a small impurity was present independent of synthesis temperature. Upon heating the impurity disappeared at 665 K after going through an intermediate phase. Rietveld analysis of multitemperature PXRD patterns collected on YAG and YbAG nanoparticles synthesized at 400 °C showed a nonlinear trend for the lattice parameter in the garnet phase. The anomaly in the lattice parameter from 565 to 865 K was proposed to be due to a complex defect mechanism involving antisite formation and vacancy reduction. Specifically, the negative thermal expansion was explained with a reduction of vacancies in the structure. At higher temperature the antisite mechanism dominates, and in the subsequently cooled sample the stoichiometry of YbAG is (Yb2.75Al0.25)24c(Al2.86)24d(Al1.75Yb0.25)16aO11.79. Hence, the garnet nanoparticles have become almost completely stoichiometric after annealing. Thermal analysis of the as-synthesized samples in inert and 20% O2 atmospheres hint that the thermal events observed correspond perfectly with the events (vacancy formation and antisite) in the defect mechanism. Furthermore, the diffusion of aluminum into the 24d site from expected amorphous parts under the evaporation of volatile species such as water was supported by the weight loss observed in the TG data. The SEM pictures after thermal analysis also showed that the nanoparticles of the phase pure YbAG do not grow significantly
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.5b01761. The unit cell of the garnet structure is shown with the specified Wyckoff sites discussed in the main paper. A schematic drawing of the continuously flow synthesis setup is shown along with a description of the synthesis procedure. Information about how the pseudosequential Rietveld refinements of YAG and YbAG were performed together with the obtained R-values is also outlined. Furthermore, overview TEM pictures for YAG and YbAG nanoparticles synthesized at 400 °C are presented along with TEM pictures of all six different samples. Elemental mapping for YAG and multitemperature PXRD patterns of YAG are shown. The measurement orders for the PXRD patterns for both samples are displayed (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest. F
DOI: 10.1021/acs.cgd.5b01761 Cryst. Growth Des. XXXX, XXX, XXX−XXX
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(31) Dobrzycki, Ł.; Bulska, E.; Pawlak, D. A.; Frukacz, Z.; Woźniak, K. Inorg. Chem. 2004, 43, 7656−7664. (32) Nørby, P.; Jensen, K. M. Ø.; Lock, N.; Christensen, M.; Iversen, B. B. RSC Adv. 2013, 3, 15368−15374. (33) Stanek, C. R.; McClellan, K. J.; Levy, M. R.; Milanese, C.; Grimes, R. W. Nucl. Instrum. Methods Phys. Res., Sect. A 2007, 579, 27− 30. (34) Jensen, K. M. Ø.; Christensen, M.; Gunnlaugsson, H. P.; Lock, N.; Bøjesen, E. D.; Proffen, T.; Iversen, B. B. Chem. Mater. 2013, 25, 2282−2290.
ACKNOWLEDGMENTS The RIKEN beamline BL4402 at SPring-8 is gratefully acknowledged for beam time. The work was supported by the Danish National Research Foundation (Center for Materials Crystallography, DNRF93) and the Danish Research Council for Nature and Universe (Danscatt).
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REFERENCES
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DOI: 10.1021/acs.cgd.5b01761 Cryst. Growth Des. XXXX, XXX, XXX−XXX
