Synthesis, thermal and dielectric characteristics of Rb<sub>5</sub>Li<sub>1/3</sub>Zr<sub>5/3</sub>(MoO<sub>4</sub>)<sub>6</sub>

This work addressed the directed synthesis of a new phase Rb 5 Li 1/3 Zr 5/3 (MoO 4 ) 6 , along with the determination of its crystallographic, thermal and electrophysical properties. The directed synthesis of the Rb 5 Li 1/3 Zr 5/3 (MoO 4 ) 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 Rb 5 Li 1/3 Zr 5/3 (MoO 4 ) 6 , crystallised in trigonal form (space group R3c, Z = 6), undergoes a diffused first-order phase transition. The structure of triple molybdate Rb 5 Li 1/3 Zr 5/3 (MoO 4 ) 6 comprises MoO 4 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 Rb 5 Li 1/3 Zr 5/3 (MoO 4 ) 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 Rb 5 Li 1/3 Zr 5/3 (MoO 4 ) 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.