Formation of Phases with the Ca3Ga2Ge4O14 Structure in Ln2O3–M2O3–GeO2–BeO (Ln = La–Gd, M = Ga, Al, Fe, Cr) Systems

Abstract

Phases of variable composition Ln₃M_{5 – 2x}Ge_{1 + x}Be_xO₁₄ (Ln = La–Gd; M = Ga, Al, Fe, Cr) with the Ca₃Ga₂Ge₄O₁₄ (GGG) structure (space group P321) were prepared by solid-phase synthesis at 1100–1400°С. In Ga systems, GGG phases are formed for La–Eu; in Al systems, for La–Gd; for Fe, only in the La system; and in Cr systems, for La–Sm. Ln₃CrGe₃Be₂O₁₄ compounds have an ordered crystal structure with oxygen octahedra occupied by Cr³⁺ ions. The other phases have an M–Ge–Be disordered structure. The compounds are decomposed in a solid phase and (or) melt incongruently.