Synthesis, thermal and dielectric characteristics of Rb₅Li_1/3Zr_5/3(MoO₄)₆

This work addressed the directed synthesis of a new phase Rb5Li1/3Zr5/3(MoO4)6, along with the determination of its crystallographic, thermal and electrophysical properties. The directed synthesis of the Rb5Li1/3Zr5/3(MoO4)6 phase was carried out using the solid-state reaction in the temperature range of 350–470 °C. According to differential scanning calorimetry, the synthesised compound Rb5Li1/3Zr5/3(MoO4)6, crystallised in trigonal form (space group R3c, Z = 6), undergoes a diffused first-order phase transition. The structure of triple molybdate Rb5Li1/3Zr5/3(MoO4)6 comprises MoO4 tetrahedra and octahedrally coordinated MO6-polyhedra. This structure is characterised by a statistical distribution of lithium and zirconium atoms in the M position (M1 = 0.790 Zr + 0.210 Li, M2 = 0.877 Zr + 0.123 Li). Rb atoms are located in the large voids of the tetrahedronoctahedral framework. The electrophysical properties of triple molybdate Rb5Li1/3Zr5/3(MoO4)6 having a scaffold structure favourable for ion transport, were studied. The correlation between dielectric and thermal characteristics in the high-temperature region near the phase transition was revealed. The temperature and frequency dependences of electrical conductivity were measured at 473–873 K in heating and cooling modes in the frequency range of 1–10 kHz. The compound exhibited a high thermally activated conductivity, reaching 1.48·10-2 Cm K/cm with activation energy in the range of 0.6–0.8 eV at a temperature of 480 °C. Well-shaped semicircles in the low-frequency region and unresolved arcs in the high-frequency region changing with increasing temperature were observed in the impedance spectra of ceramic Rb5Li1/3Zr5/3(MoO4)6 sample at various temperatures. The evolution of the imaginary part (Z'') as a function of the real part (Z') of the complex impedance resembled that of the complex impedance for compounds having ionic conductivity.

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.

The crystal growth and properties of novel magnetic double molybdate RbFe5(MoO4)7 with mixed Fe3+/Fe2+ states and 1D negative thermal expansion

Single crystals of new composition RbFe₅(MoO₄)₇ were successfully grown by the flux method, and their crystal structure was determined using the X-ray single-crystal diffraction technique.

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.