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

• Published in: Journal of alloys and compounds 2021-08, Vol.873, p.159828, Article 159828
• Main Authors: Grossman, Victoria G., Molokeev, Maxim S., Bazarov, Bair G., Bazarova, Jibzema G.
• Format: Article
• Language: English
• Subjects: Conducting material; Conductors; Crystal structure; DSC; Electrical resistivity; Ion currents; Molybdates; Parameters; Phase diagram; Potassium; Rietveld method; Synthesis; Thallium; Thermal stability; Unit cell; X ray powder diffraction
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2021.159828

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) Å, V = 3526.14 (4) Å3, Z = 6 for K5CrHf(MoO4)6and a = b = 10.53406 (12), c = 37.6837 (5) Å, V = 3621.39 (9) Å3, 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) Å, V = 1716.78 (6) Å3, 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) (σ = 5.22 × 10−4 S / cm for K5CrHf(MoO4)6, σ = 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 (σ = 4.42 × 10−6 S / cm at 773 K). •The subsolidus phase relations in the M2MoO4–Cr2(MoO4)3–Hf(MoO4)2 (M = K, Tl) systems were studied.•Structures of M5CrHf(MoO4)6 (M = K, Tl) and TlCrHf0.5(MoO4)3 were solved.•The electrophysical and thermal properties of M5CrHf(MoO4)6 (M = K, Tl) and TlCrHf0.5(MoO4)3 molybdates were studied.•It was found that Tl5CrHf(MoO4)6 is a good ionic conductor with a conductivity of about 10−2 S / cm.