Orthoborates LiCdRE5(BO3)6 (RE = Sm–Lu and Y) with Rare-Earth

Jun 29, 2017 - For example, Eu3+- or Tb3+-doped rare-earth borate hosts served as solid-state lighting because of their low cost and high chemical and...
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Orthoborates LiCdRE5(BO3)6 (RE = Sm−Lu and Y) with Rare-Earth Ions on a Triangular Lattice: Synthesis, Crystal Structure, and Optical and Magnetic Properties Mingjun Xia,† Kun Zhai,‡ Jun Lu,‡ Young Sun,‡ and R. K. Li*,† †

Beijing Center for Crystal Research and Development, Key Laboratory of Functional Crystals and Laser Technology, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China ‡ Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China S Supporting Information *

ABSTRACT: Single crystals of LiCdY5(BO3)6 were successfully grown from a Li2O−B2O3 flux, and its lanthanide homotypic compounds, LiCdRE5(BO3)6 (RE = Sm−Lu), have been prepared by solid-state reaction. They crystallize in the noncentrosymmetric space group P6522 with cell parameters in the ranges of a = 7.0989(2)−6.9337(1) Å and c = 25.9375(1)−24.8960(6) Å. As a representative example, LiCdY5(BO3)6 features a triangular lattice in the ab plane composed of three distinct crystallographic Y sites. The triangular lattices spaced with the same distance of 1 c 6 are further stacked to build three-dimensional frameworks by reinforcement of the isolated planar BO3 groups and distorted LiO4 tetrahedra. Magnetic measurements show that Eu and Sm compounds exhibit typical Van Vleck-type paramagnetism and other rare-earth borates show weak antiferromagnetic behavior. In addition, UV−vis−near-IR diffuse-reflectance and photoluminescence spectra were performed to understand the transition energy levels of active rareearth ions and their relationships to magnetism.

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INTRODUCTION Rare-earth borates have attracted much interest for their wide application in optoelectronics because of their abundant chemical and physical properties. For example, Eu3+- or Tb3+doped rare-earth borate hosts served as solid-state lighting because of their low cost and high chemical and thermal stability.1−3 Additionally, several noncentrosymmetric (NCS) rare-earth borates such as La2CaB10O19,4 Na3La9O3(BO3)8,5 YAl3(BO3)4 (YAB),6 YCa4O(BO3)3 (YCOB),7 and GdCa4O(BO3)3 (GdCOB)8 crystals were proposed as nonlinear-optical (NLO) crystals with large NLO susceptibilities, a high laser damage threshold, good mechanical and crystal growth behavior, and nonhygroscopic properties. Because they can generate laser radiation and simultaneously double the frequency of the fundamental laser, self-frequency-doubling (SFD) crystals of the above NLO crystals doped with another rare-earth active ion (usually Nd3+ or Yb3+) are also intensively studied for their application in microchip lasers. Among these SFD crystals, Nd:YAB, Nd:YCOB, and Nd:GdCOB were thoroughly investigated.9−11 Besides, some borate compounds containing high Tb content with high symmetry such as trigonal, tetrahedral, hexagonal, or cubic were proposed as promising magnetooptical crystals with high transmission in the UV region and large Verdet constants, for example, Sr3Tb(BO3)3,12 LiCaTb5(BO3)6,13 SrLiTb2(BO3)3.14 Recently, we have studied the rare-earth borate system and found dozens of new compounds. In this report, the Li2O− CdO−Y2O3−B2O3 system was explored to search for new © 2017 American Chemical Society

functional materials, and a single crystal of LiCdY5(BO3)6 with high Y content and hexagonal structure was obtained. Because of the similar crystal chemical behavior of Y3+ and rare-earth RE3+ cations, a series of compounds, LiCdRE5(BO3)6 (RE = Sm−Lu), were prepared following the discovery of the Y compound.

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EXPERIMENTAL SECTION

Experimental Methods. X-ray diffraction (XRD) data were collected on a Bruker D8 Focus powder X-ray diffractometer using Cu Kα radiation (λ = 1.54178 Å) at room temperature in the 2θ range of 7−70°. The cell parameters of the polycrystalline LiCdRE5(BO3)6 (RE = Sm−Lu and Y) samples were obtained by the LeBail fit using the GSAS and EXPGUI software packages with a single-crystal structure of LiYCd5(BO3)6 as the starting model.15,16 The thermal properties were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) using a NETZSCH STA 449C TGA/DSC/differential thermal analysis thermal analyzer in a nitrogen atmosphere. UV−vis−near-IR (NIR) diffuse-reflectance spectra were measured on a Varian Cary 5000 spectrophotometer equipped with an integrating sphere. BaSO4 was employed as the reference (100% reflectance). Room temperature photoluminescence (PL) excitation and emission spectra were recorded on an Edinburg FLS980 fluorescence spectrophotometer in the range of 200−800 nm. A 1064 nm fundamental light emitted from a Q-switched Nd:YAG laser was used for second-harmonic-generation (SHG) tests, and the SHG signal, i.e., 532 nm light, was detected by a photomultiplier tube. The Received: March 29, 2017 Published: June 29, 2017 8100

DOI: 10.1021/acs.inorgchem.7b00756 Inorg. Chem. 2017, 56, 8100−8105

Article

Inorganic Chemistry temperature dependence of the magnetic susceptibilities of LiCdRE5(BO3)6 (RE = Sm−Yb) were measured on a SQUID magnetometer (Quantum Design MPMS-7) from 2 to 300 K in an applied magnetic field of 1000 Oe. According to the standard preparation process, the sample was inserted in a gelatin capsule and then mounted in a straw. All accessories (Quantum Design Inc.) have negligible contribution to our measurement results. Single-Crystal Growth of LiCdY5(BO3)6. All starting materials are analytically pure commercial reagents as received. The chemicals of CdO (3.8523 g, 0.03 mol), Li2CO3 (2.9556 g, 0.04 mol), H3BO3 (18.5499 g, 0.3 mol), and Y2O3 (4.6152 g, 0.02 mol) were thoroughly ground and placed in a Pt crucible. The mixture was slowly heated to 940 °C, held for several hours to homogenize, and then cooled to 800 °C at a rate of 5 °C/h before the furnace was switched off. Colorless plate-shaped crystals were obtained and mechanically separated from the surface of the crucible’s content. Syntheses of LiCdRE5(BO3)6 (RE = Sm−Lu and Y). After the composition of LiYCd5(BO3)6 was obtained from structure determination, the polycrystalline sample of Y and its lanthanide homotypic compounds were synthesized by a high-temperature solid-state reaction method. Stoichiometric chemicals of Li2CO3, CdO, H3BO3, Y2O3, Tb4O7, and RE2O3 were mixed and ground thoroughly using an agate mortar and then preheated at 500 °C for 12 h to decompose carbon dioxide and water. Finally, the mixtures were calcined at 950− 1000 °C for 24 h with several intermediate grindings. All sample purities were checked by powder XRD (PXRD) analysis. Structure Determination. Single-crystal XRD data were recorded on a Rigaku XtalLAB mini-diffractometer equipped with graphitemonochromated Mo Kα radiation (λ = 0.71073 Å) at room temperature. The systematic absences of the intensity data were checked by XPREP software, giving 20 possible space group choices. The space group P65 (or P61) was first tried to solve the structure with direct methods by SHELXS-97 and refined by the full-matrix least squares on F2 by SHELXL-97, respectively.17 The structure was checked by the ADDSYM algorithm using PLATON software,18 and the new space group P6522 was suggested, which gave a more satisfactory structure solution. In the refinement, judging from the atomic thermal displacement parameters, Cd3 was refined with Y3 with a disorder ratio of 1:1, and the Li atom was also refined with an occupancy of 0.5 for charge balance. The detailed crystallographic data are summarized in Table 1. The atomic coordinates, occupancies, and equivalent displacement parameters are given in Table 2. The important bond lengths are listed in Table 3.

patterns, and the other rare-earth analogues are of pure phase and adopted the Y compound. The detailed refinement plots of the PXRD patterns for LiCdRE5(BO3)6 (RE = Sm−Lu and Y) are presented in Figures S1−S11. The lattice parameters of rare-earth borates were obtained by the LeBail fit and decrease with an increase of the atomic numbers with small ionic radii. Also, the cell volumes almost obey linear contraction due to the lanthanide contraction effect (Figure 2). Analysis of TGA and DSC shows that LiCdY5(BO3)6 started to lose weight and decompose at heating temperatures above 1000 °C (Figure S12). The PXRD patterns at different temperatures also indicate that LiCdY5(BO3)6 decomposes to YBO3 as the main phase, further confirming its incongruent melt property (Figure S13). Crystal Structure. LiCdY5(BO3)6 crystallizes into the NCS space group P6522 with cell parameters of a = 7.0132(6) Å, c = 25.370(4) Å, and Z = 3. As displayed in Figure 3a, there are two distinct B atoms in the unit cell, both of which coordinate to three O atoms to form planar BO3 groups with bond lengths of 1.340(10)−1.387(9) Å and bond angles of 117.9(7)− 123.7(11)°. The Y1 and Y3/Cd3 atoms are surrounded by six O atoms, forming a distorted octahedron, with C2 point group symmetry and bond distances ranging from 2.230(5) to 2.365(5) Å. The Y2 atoms also with C2 symmetry coordinate to eight O atoms, revealing six normal [2.292(5)−2.332(5) Å] and two long [2.716(5) Å] bonds. As shown in Figure 3b, Y1O6 and Y3/Cd3O6 distorted octahedra were linked by corner-sharing O5 atoms to form (Y2O10)14− chains along the ⟨110⟩ direction. Then the adjacent chains are connected via Y2O8 polyhdera to build two-dimensional sheets. Also the three Y atoms form layers of two-dimensional triangular lattice in the ab plane (Figure 3c). Because three Y atoms sit in the same position along the c axis, the layers are completely parallel and the distances between two adjacent layers are 1 c. Finally, the 6 layers are further connected via O atoms and reinforced by BO3 groups along the c direction to build three-dimensional frameworks. The Li atom forms two short [2.14(4) Å] and two long [2.42(4) Å] bonds in a distorted tetrahedral environment and resides in the void within the framework. Optical Properties. The absorption spectra were converted from the reflectance spectra according to the Kubelka−Munk function: α/S = (1 − R)2/2R, where α, S, and R are the absorption, scattering, and reflectance coefficients, respectively.19 According to absorption spectra, LiCdRE5(BO3)6 (RE = Sm−Tm) has absorption peaks in the range of 200− 900 nm resulting from f−f or f−d transitions of RE3+ (Figure S14). Also, the band gaps of the compounds are obtained as 5.10, 4.05, 3.36, 4.53, 4.86, 5.79, 5.74, 5.56, 4.79, 3.53, and 3.25 eV for LiCdRE5(BO3)6 (RE = Sm−Lu and Y), according to the reflectance spectra (Figures S15−S25). Although the LiCdRE5(BO3)6 (RE = Sm−Lu and Y) series of compounds crystallizes into the NCS space group P6522, all NLO coefficient components are zero by considering Kleinman symmetry. Thus, they are not SHG-active, which is in agreement with no observable green-light signal in the SHG tests. The PL spectra were measured for the Sm and Eu analogues. As shown in Figure 4a, the emission spectrum of the Sm compound is composed of four emission bands corresponding to transitions from 4G5/2 to 6H5/2 (562 nm), 6 H7/2 (599 nm), 6H9/2 (646 nm), and 6H11/2 (710 nm) under 362 nm excitation. Theoretically, the ground state 6H5/2 may be further decomposed to maximally six (2J + 1) small peaks

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RESULTS AND DISCUSSION Syntheses. As shown in Figure 1, the PXRD patterns of LiCdY5(BO3)6 are in good agreement with the calculated Table 1. Crystallographic Data for LiCdY5(BO3)6 empirical formula fw wavelength (Å) cryst syst space group a (Å) c (Å) volume (Å3) Z density (g/cm3) μ (mm−1) F(000) GOF on F2 R(F)a Rw(Fo2)b

R(F) = ∑||Fo| − |Fc||/∑|Fo|. ∑[w(Fo2)2]}1/2. a

LiCdY5(BO3)6 916.75 0.71073 hexagonal P6522 (No. 179) 7.0132(6) 25.370(4) 1080.6(2) 3 4.226 21.461 1260 1.061 0.0559 0.1010 b

Rw(Fo2) = {∑[w(Fo2 − Fc2)2]/ 8101

DOI: 10.1021/acs.inorgchem.7b00756 Inorg. Chem. 2017, 56, 8100−8105

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Inorganic Chemistry Table 2. Atomic Coordinates and Equivalent Isotropic Displacement Parameters for LiCdY5(BO3)6a

a

atom

Wyckoff site

x

y

z

SOF

Ueq

Y1 Y2 Y3 Cd3 O1 O2 O3 O4 O5 B1 B2 Li

6b 6b 6b 6b 12c 6a 12c 12c 12c 12c 6a 6a

0.01316(10) 0.33023(8) 0.33816(13) 0.33816(13) 0.3411(9) −0.1039(11) 0.0926(10) 0.6107(9) 0.3286(8) 0.3366(15) 0.7017(18) 0.357(6)

−0.01316(10) 0.66977(8) 0.66908(7) 0.66908(7) 0.5587(9) 0 −0.2486(10) 0.6072(9) 0.2937(9) 0.3669(15) 0.7017(18) 0

0.0833 0.0833 −0.0833 −0.0833 −0.0011(2) 0 0.0370(2) −0.1188(2) 0.0569(2) 0.0057(3) −0.1667 0

1 1 0.5 0.5 1 1 1 1 1 1 1 0.5

0.0111(3) 0.0137(4) 0.0197(4) 0.0197(4) 0.022(2) 0.022(2) 0.024(2) 0.021(2) 0.020(2) 0.010(2) 0.012(3) 0.019(2)

Ueq is defined as one third of the trace of the orthogonalized Uij tensor.

Table 3. Selected Bond Lengths (Å) and Angles (deg) for LiCdY5(BO3)6 Y1−O5 Y1−O2 Y1−O3 Y2−O1 Y2−O4 Y2−O3 Y2−O5 Y3−O1 Y3−O4 Y3−O5

(×2) (×2) (×2) (×2) (×2) (×2) (×2) (×2) (×2) (×2)

2.283(5) 2.287(3) 2.310(6) 2.292(5) 2.320(5) 2.332(5) 2.716(5) 2.230(5) 2.341(5) 2.365(5)

B1−O1 B1−O3 B1−O5 B2−O2 B2−O4 (×2) Li1−O3 (×2) Li1−O4 (×2)

1.340(10) 1.376(10) 1.387(9) 1.364(14) 1.379(8) 2.03(2) 2.14(4)

O1−B1−O5 O1−B1−O3 O3−B1−O5 O2−B2−O4 (×2) O4−B2−O4

117.9(7) 120.5(7) 121.6(7) 118.1(5) 123.7(11)

Figure 2. Cell parameters of LiCdRE5(BO3)6 (RE = Sm−Lu and Y).

LiCdRE5(BO3)6 (RE = Sm−Yb) are given in Figure 5. At elevated temperatures, the rare-earth borates obey Curie− Weiss law except for the Sm and Eu analogues.20−26 As reported in many Sm3+ compounds, LiCdSm5(BO3)6 also exhibits Van Vleck-type paramagnetism.22,27 0.1241 [2.14δ + 3.67 + (42.9δ + 0.82)e−7δ χ (Sm 3 +) = δT

Figure 1. PXRD patterns of LiCdRE5(BO3)6 (RE = Sm−Lu and Y).

because of the crystal-field-splitting (CFS) effect. Our observation is that six peaks are at 557.5, 562.2, 562.4, 562.5, 566.8, and 569.2 nm, corresponding to the CFS of Δ1 ≈ Δ2 ≈ Δ3 ≈ 156 cm−1, Δ4 = 294 cm−1, and Δ5 = 369 cm−1. The emission spectrum of the Eu compound exhibits several emission bands in the range from 500 to 750 nm, which are from the transitions of 5D0 → 7FJ (J = 0, 1, 2, 3, and 4). The observed splitting of the J > 0 bands are also caused by the CFS. Magnetic Properties. The temperature-dependent molar magnetic susceptibilities and the inverse susceptibilities of

+ (142δ − 0.33)e−16δ + ...] /(3 + 4e−7δ + 5e−16δ + ...)

(1)

where δ = 27λ/110kT and λ and k are the spin−orbit coupling (SOC) and Boltzmann constants, respectively. The deduced SOC constant is obtained as 450 K, in good accordance with the experimental value (444 K) from the fluorescence spectra of the ground state (blue curve in Figure 5b). However, as 8102

DOI: 10.1021/acs.inorgchem.7b00756 Inorg. Chem. 2017, 56, 8100−8105

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Inorganic Chemistry

the magnetic susceptibility of LiCdEu5(BO3)6 can be given by the following equation (Van Vleck contribution):22,23,27 χ (Van Vleck) =

0.1241 [24 + (13.5γ − 1.5)e−γ γT + (67.5γ − 2.2)e−3γ + (189γ − 3.5)e−6γ ] /(1 + 3e−γ + 5e−3γ + 7e−6γ + ...)

(2)

with γ = λ/kT. λ is the SOC constant. As shown in Figure 5c, the magnetic susceptibility of LiCdEu5(BO3)6 shows an upturn below 10 K. By taking into account the paramagnetic impurity contribution, the magnetic susceptibility in the whole measured temperature range can be fitted very well using the following expression (the tail 0.0008/T is from the paramagnetic impurity contribution): χ (Eu 3 +) = χ (Van Vleck) +

0.0008 T

(3)

According to eqs 2 and 3, the SOC constant λ is fitted as 425 K, which is in good agreement with the energy separation level (418 K) between 7F0 and 7F1 acquired from the fluorescence spectra. The effective magnetic moments per RE3+ of Gd, Tb, Dy, Ho, Er, Tm, and Yb compositions were obtained as 8.17, 9.65, 11.01, 10.64, 9.59, 7.90, and 4.71 μB by fitting inverse susceptibility data at the high-temperature region. These values are all close to the theoretical free-ion values of 7.94, 9.73, 10.63, 10.60, 9.57, 7.63, and 4.50 μB for Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, and Yb3+, respectively. In addition, the small negative Weiss temperatures indicate that the antiferromagnetic interaction is weak between the magnetic ions. It is worth noting that similar to our previously reported LiCaTb5(BO3)6, the Tb analogue of the present compound may also be employed as a magnetooptical material because of its high Tb3+ content and uniaxial crystal symmetry. As shown in Figure 6, the saturation magnetization of LiCdTb5(BO3)6 at 2 K is 5.29 μB under a magnetic field of 9 T, which is smaller than the theoretical value. The reason may be due to the strong singleion-anisotropy characteristic of Tb3+, as explained in our previous work.

Figure 3. (a) Crystal structure of LiCdY5(BO3)6. (b) Twodimensional layer at the ab plane. (c) Triangular structure of Y layers. Color code: blue, Y; black, Y/Cd; green, B; red, O; yellow, Li.

shown in Figure 5b and in other reports,22,23 the magnetic susceptibility of LiCdSm5(BO3)6 generally does not follow the above equation below 200 K. We found that, by incorporating the effect of the CFS as observed in the fluorescence spectra, improvement in the fit was very good in the whole temperature range with the CFS constants of 50 and 250 K, also in reasonable agreement with the observed CFS values of 15 and 210 K from the fluorescence spectra (red curve in Figure 5b). The magnetic susceptibility for LiCdEu5(BO3)6 typically increases with decreasing temperature and flattens out below 100 K, exhibiting typical Van Vleck paramagnetism. By considering the contribution from the excited states of Eu3+,

Figure 4. PL spectra of (a) LiCdSm5(BO3)6 and (b) LiCdEu5(BO3)6 at room temperature. 8103

DOI: 10.1021/acs.inorgchem.7b00756 Inorg. Chem. 2017, 56, 8100−8105

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Figure 5. (a) Temperature dependence of the magnetic susceptibilities of LiCdRE5(BO3)6 (RE = Sm−Yb). (b) Van Vleck and CFS fitting of LiCdSm5(BO3)6. (c) Van Vleck fitting of LiCdEu5(BO3)6. (d) Inverse magnetic susceptibilities of LiCdRE5(BO3)6 (RE = Gd−Yb).

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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.inorgchem.7b00756. Refinement plots of PXRD patterns, DSC and TGA curves, XRD patterns, and absorption and UV−vis−NIR spectra (PDF) Accession Codes

CCDC 1553817 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_ [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

Figure 6. Field-dependent magnetization for LiCdTb5(BO3)6 at 2 K.

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CONCLUSION A series of new borates LiCdRE5(BO3)6 (RE = Sm−Lu and Y) have been successfully obtained, and LiCdY5(BO3)6 was grown as a single crystal. The structures of these compounds feature a triangular lattice in the ab plane composed of three distinct crystallographic rare-earth sites, and the layers of the triangular lattice are further interlinked by the planar BO3 groups through O atoms. Magnetic measurements on LiCdRE5(BO3)6, except for the Sm and Eu analogues, show weak antiferromagnetic exchange interactions. LiCdEu5(BO3)6 features typical Van Vleck paramagnetism, while LiCdEu5(BO3)6 exhibits both Van Vleck paramagnetism and CFS, as confirmed from fluorescent spectra. Also, the LiCdTb5(BO3)6 crystal may serve as a new magnetooptical material because of its high Tb3+ content and high symmetry.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Mingjun Xia: 0000-0001-8092-6150 Young Sun: 0000-0001-8879-3508 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (Grant 51502307), National Instrumentation Program (Grant 2012YQ120048), and 8104

DOI: 10.1021/acs.inorgchem.7b00756 Inorg. Chem. 2017, 56, 8100−8105

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Inorganic Chemistry

(20) Sanders, M. B.; Krizan, J. W.; Cava, R. J. RE3Sb3Zn2O14 (RE = La, Pr, Nd, Sm, Eu, Gd): a new family of pyrochlore derivatives with rare earth ions on a 2D Kagome lattice. J. Mater. Chem. C 2016, 4, 541−550. (21) Latshaw, A. M.; Wilkins, B. O.; Hughey, K. D.; Yeon, J.; Williams, D. E.; Tran, T. T.; Halasyamani, P. S.; zur Loye, H. M. A5RE4X[TO4]4 crystal growth and photoluminescence. Fluoride flux synthesis of sodium and potassium rare earth silicate oxyfluorides. CrystEngComm 2015, 17, 4654−4661. (22) Puche, R. S.; Norton, M.; White, T. R.; Glaunsinger, W. S. Magnetic Properties of the Semiconducting Lanthanide Cuprates Ln2CuO4 and Their Interpretation: Evidence for a New Series of Planar Copper Antiferromagnets. J. Solid State Chem. 1983, 50, 281− 293. (23) Rukang, L.; Kremer, R. K.; Maier, J. The synthesis and characterization of a new family of single layer cuprates LnBaCuO2BO3 (Ln = La, Pr, Nd, Sm, Eu and Gd). Phys. C 1993, 213, 26− 32. (24) Feng, J. H.; Hu, C. L.; Xu, X.; Kong, F.; Mao, J. G. Na2RE2TeO4(BO3)2 (RE = Y, Dy−Lu): Luminescent and Structural Studies on a Series of Mixed Metal Borotellurates. Inorg. Chem. 2015, 54, 2447−2454. (25) Lin, J.; Diefenbach, K.; Silver, M. A.; Dalal, N. S.; AlbrechtSchmitt, T. E. Structure−Property Correlations in the Heterobimetallic 4f/3d Materials Ln2M(TeO3)2(SO4) (Ln = Y, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu; M = Co or Zn). Cryst. Growth Des. 2015, 15, 4606−4615. (26) Sanjeewa, L. D.; Fulle, K.; McMillen, C. D.; Wang, F. L.; Liu, Y. F.; He, J.; Anker, J. N.; Kolis, J. W. Hydrothermal synthesis, structure, and property characterization of rare earth silicate compounds: NaBa3Ln3Si6O20 (Ln = Y, Nd, Sm, Eu, Gd). Solid State Sci. 2015, 48, 256−262. (27) Van Vleck, J. H. The Theory of Electric and Magnetic Susceptibilities; Oxford University Press: London, 1965.

Foundation of the Director of Technical Institute of Physics and Chemistry, Chinese Academy of Sciences.

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DOI: 10.1021/acs.inorgchem.7b00756 Inorg. Chem. 2017, 56, 8100−8105