Application of KR₃F₁₀ (R = Gd–Lu and Y) Polymorphism for Modeling the Defect Structure of Nonstoichiometric Multicomponent Fluorite-Type Crystals in T-x Systems

Abstract

Nonstoichiometric nanostructured crystals (NSC) α-M 0.5−x R 0.5+x F 2+2x (M = Na and K; R = Sc, Y, and La−Lu) and M 1−x R x F 2+x (M = Ca, Sr, Ba, Cd, and Pb) with a f luorite-type (F) structure are widely used in quantum electronics, optics, solid-state ionics (superionic conductors), and bioimaging. However, the temperature dependence of their defect crystal structure, which is fundamental for understanding the numerous properties of F-NSC, remains unexplored. In this study, temperature changes in the F-NSC defect structure in T-x (temperature-composition) systems were simulated. Data on the KR 3 F 10 (R = Gd−Lu and Y) polymorphism were used for modeling. A fragment representing an octacubic cluster (OCC) [M 14−n R n F 64+n ] with a hybrid-type (i-f-) anionic core was isolated in the structure of low-temperature β-KR 3 F 10 (R = Er and Yb). It includes all types of interstitial anions involved in the formation of i-and f-type clusters in the unif ied cluster model (UCM) of the F-NSC defect structure. There is a common tendency for hybrid (i + f) and f-type OCCs to form at low T and i-type OCCs at high T. The UCM was applied to verify T changes in the Ca 0.94 Y 0.06 F 2.06 defect structure within the 293 ÷ 1423 K T range.