Synthesis and characterization of a new magnesium molybdates Tl1.85M0.15Mg2(MoO4)3 (M = K, Rb) with a langbeinite type structure

In this work we have successfully synthesized pure phases of Tl1.85M0.15Mg2(MoO4)3 (M = K, Rb) langbeinite powders using the solid-state reaction method. Structural characterization was carried out via the Rietveld method on the X-ray powder diffraction data. The following unit cell parameters are calculated for Tl1.85K0.15Mg2(MoO4)3: a = 10.68509(16) Å, V = 1219.93(6) Å3, and for Tl1.85Rb0.15Mg2(MoO4)3: a = 10.69463(9) Å, V = 1223.20(3) Å3. The electrical conductivity was studied by impedance spectroscopy in the [473–1010 K] temperature range and results show that the Tl1.85M0.15Mg2(MoO4)3 (M = K, Rb) were ionic solid electrolyte conductors. Results also show that Tl1.85K0.15Mg2(MoO4)3 has the highest electrical conductivity.