Structural, thermal and optical properties of elpasolite-like (NH4)(2)KZrF7

Pogoreltsev, E., I; Mel'nikova, S., V; Molokeev, M. S.; Flerov, I. N.; Laptash, N. M. Source: JOURNAL OF SOLID STATE CHEMISTRY, 277 376-380; 10.1016/j.jssc.2019.06.013 SEP 2019

New fluoride compound (NH₄)₂KZrF₇ with the elpasolite structure (sp. gr. Fm-3m) was synthesized by partial cationic substitution in (NH₄)₃ZrF₇ cryolite. Due to small difference in ionic radii of K⁺ and NH₄⁺, non-equivalent crystallographic positions 8c and 4b are occupied by both cations. Investigations of thermal, optical and structural properties in a wide range of temperature revealed two phase transitions Fm-3m ↔ P4₂/ncm ↔ P4₂/nmc of the first order. The results obtained are discussed in comparison with the data for the previously studied related cryolite (NH₄)₃ZrF₇