Potassium and thallium conductors with a trigonal structure in the M2MoO4-Cr2(MoO4)3-Hf(MoO4)2 (M = K, Tl) systems: Synthesis, structure, and ionic conductivity

The triple molybdates M5CrHf(MoO4)6 (M = K, Tl) and TlCrHf0.5(MoO4)3 were found upon studying the corresponding ternary molybdate systems M2MoO4-Cr2(MoO4)3-Hf(MoO4)2 (M = K, Tl) in the subsolidus region using X-ray powder diffraction. The crystal structures of M5CrHf(MoO4)6 (M = K, Tl) and TlCrHf0.5(MoO4)3 are refined by Rietveld method. M5CrHf(MoO4)6 (M = K, Tl) crystallizes in space group R3 c with unit cell parameters: a = b = 10.45548 (5), c = 37.24614 (3) angstrom, V = 3526.14 (4) angstrom 3, Z = 6 for K5CrHf(MoO4)6 and a = b = 10.53406 (12), c = 37.6837 (5) angstrom, V = 3621.39 (9) angstrom 3, Z = 6 for Tl5CrHf(MoO4)6. TlCrHf0.5(MoO4)3 crystallizes in space group R3 with unit cell parameters: a = b = 12.9710 (2), c = 11.7825 (2) angstrom, V = 1716.78 (6) angstrom 3, Z = 6. The thermal stability and electrical conductivity of the new compounds were investigated. Electrical conductivity measurements gave high values for the triple molybdates M5CrHf(MoO4)6 (M = K, Tl) (sigma = 5.22 & times; 10 & minus;4 S / cm for K5CrHf(MoO4)6, sigma = 1.1 10-2 S / cm for Tl5CrHf(MoO4)6 at 773 K) and relatively low values for the triple molybdate TlCrHf0.5(MoO4)3 (sigma = 4.42 & times; 10-6 S / cm at 773 K). (c) 2021 Published by Elsevier B.V.

Automated summary

New triple molybdates M5CrHf(MoO4)6 (M = K, Tl) and TlCrHf0.5(MoO4)3 were discovered in the ternary molybdate systems M2MoO4-Cr2(MoO4)3-Hf(MoO4)2 (M = K, Tl) in the subsolidus region. The crystal structures were refined and their thermal stability and electrical conductivity were investigated, showing high values for the former and relatively low values for the latter.