CuX sub(2)O sub(6) and Ba sub(3)CuX sub(2)O sub(9) (X identical with Nb, Ta): Influence of the preparation conditions on phase formation and phase composition

• Published in: Solid state ionics 1997-11, Vol.101-103, p.579-584
• Main Authors: Langbein, H, Bremer, M, Krabbes, I
• Format: Article
• Language: English
• ISSN: 0167-2738

The title compounds were prepared by conventional solid state reaction and by thermal decomposition of freeze-dried oxalate precursors using different temperature regimes. The thermal decomposition of an appropriately composed oxalate precursor enables the direct synthesis of pure monoclinic CuNb sub(2)O sub(6), thermodynamically stable only at theta less than or equal to 700 degree C. The solid state reaction leads to the orthorhombic columbite type phase or to a mixture of the orthorhombic and monoclinic phases. A new metastable CuTa sub(2)O sub(6)-trirutile phase was synthesized by thermal decomposition of an oxalate precursor. Above 800 degree C, the decomposition results in the already known perovskite-like structure. Tetragonal perovskites Ba sub(3)Cu sub(1+x)Nb sub(2-x)O sub(9-1.5x) and Ba sub(3)Cu sub(1+x)Ta sub(2-x)O sub(9-1.5x) were synthesized by solid state reaction and by precursor decomposition. The phase formation and homogeneity of the perovskites strongly depends on the reaction conditions.