Phase relations in the Me2MoO4–In2(MoO4)3–Hf(MoO4)2 systems, where Me = Li, K, Tl, Rb, Cs

Received: 26.09.2018. Accepted: 12.10.2018. Published: 31.10.2018.The Me2MoO4–In2(MoO4)3–Hf(MoO4)2 systems where Me = Li, K, Tl, Rb, Cs were studied in the subsolidus region using an X-ray powder diffraction. Quasi-binary joins were revealed, and triangulation carried out. The formation of ternary molybdates Me5InHf (MoO4)6 for Me = K, Tl, Rb, Cs and Мe2InHf2(MoO4)6.5 for Me = Rb, Cs was established.The work was carried out according to the state assignment BINM SB RAS (project no. 0339‑2016‑0007) and RFBR, grants Nos. 18‑03‑00799

Electronic structure of β-RbSm(MoO4)(2) and chemical bonding in molybdates

Microcrystals of orthorhombic rubidium samarium molybdate, β-RbSm(MoO4)2, have been fabricated by solid state synthesis at T = 450 °C, 70 h, and at T = 600 °C, 150 h. The crystal structure has been refined by the Rietveld method in space group Pbcn with cell parameters a = 5.0984(2), b = 18.9742(6) and c = 8.0449(3) Å (RB = 1.72%). Thermal properties of β-RbSm(MoO4)2 were traced by DSC over the temperature range of T = 20–965 °C, and the earlier reported β ↔ α phase transition at T ∼ 860–910 °C was not verified. The electronic structure of β-RbSm(MoO4)2 was studied by employing theoretical calculations and X-ray photoelectron spectroscopy. It has been established that the O 2p-like states contribute mainly to the upper part of the valence band and occupy the valence band maximum, whereas the Mo 4d-like states contribute mainly to the lower part of the valence band. Chemical bonding effects have been analysed from the element core level binding energy data. In addition, it was found that the luminescence spectrum of β-RbSm(MoO4)2 is rather peculiar among the Sm3+ containing materials. The optical refractive index dispersion in β-RbSm(MoO4)2 was also predicted by the first-principles calculations

Exploration of structural, thermal, vibrational and spectroscopic properties of new noncentrosymmetric double borate Rb3NdB6O12

New noncentrosymmetric rare earth borate Rb3NdB6O12 is found in the ternary system Rb2O–Nd2O3–B2O3. The Rb3NdB6O12 powder was fabricated by solid state synthesis at 1050 K for 72 h and the crystal structure was obtained by the Rietveld method. Rb3NdB6O12 crystallized in space group R32 with unit cell parameters a = 13.5236(4), c = 31.162(1) Å, Z = 3. From DSC measurements, the reversible phase transition (I type) in Rb3NdB6O12 is observed at 852–936 K. The 200 μm thick tablet is transparent over the spectral range of 0.3–6.5 μm and the band gap is found as Eg ∼ 6.29 eV. Nonlinear optical response of Rb3NdB6O12 tested via SHG is estimated to be higher than that of K3YB6O12. Blue shift of Nd luminescent lines is found in comparison with other borates. The vibrational parameters of Rb3NdB6O12 are evaluated by experimental methods

The crystal growth and properties of novel magnetic double molybdate RbFe5_{5}(MoO4_{4})7_{7} with mixed Fe3+^{3+}/Fe2+^{2+}states and 1D negative thermal expansion

Single crystals of new compound RbFe$_5$(MoO$_4$)$_7$ were successfully grown by the flux method, and their crystal structure was determined using the X-ray single-crystal diffraction technique. The XRD analysis showed that the compound crystallizes in the monoclinic space group P21/m, with unit cell parameters a = 6.8987(4), b = 21.2912(12) and c = 8.6833(5) Å, β = 102.1896(18)°, V = 1246.66(12) Å$^3$, Z (molecule number in the unit cell) = 2, R-factor (reliability factor) = 0.0166, and T = 293(2) K. Raman spectra were collected on the single crystal to show the local symmetry of MoO$_4$ tetrahedra, after the confirmation of crystal composition using energy dispersive X-ray spectroscopy (EDS). The polycrystalline samples were synthesized by a solid-state reaction in the Ar atmosphere; the particle size and thermal stability were investigated by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) analyses. The compound decomposes above 1073 K in an Ar atmosphere with the formation of Fe(III) molybdate. The thermal expansion coefficient along the c direction has the value α = −1.3 ppm K$^{−1}$ over the temperature range of 298–473 K. Magnetic measurements revealed two maxima in the magnetization below 20 K, and paramagnetic behavior above 50 K with the calculated paramagnetic moment of 12.7 μB per formula unit is in good agreement with the presence of $_3$Fe$^{3+}$ and $_2$Fe$^{3+}$ in the high-spin (HS) state. The electronic structure of RbFe5(MoO4)7 is comparatively evaluated using X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations

Synthesis and luminescent properties of new tungstates Ln2Zr(WO4)5 (Ln = Tb, Dy)

New polycrystalline powder samples of double Ln2Zr(WO4)5 (Ln = Dy, Tb) tungstates were synthesized using high-temperature solid-phase and sol-gel methods. The conditions of the sol-gel synthesis of tungstates were optimized. The obtained phases were characterized by the X-ray powder diffraction on the basis of the crystallographic data of similar Ln–Zr molybdates. It is found that Ln2Zr(WO4)5 (Ln = Dy, Tb) double tungstates crystallize in the orthorhombic crystal system, space group Cmc21 (Z = 4). The intensive luminescence in the green spectral region for Tb2Zr(WO4)5 and yellow spectral region for Dy2Zr(WO4)5 was shown