Preparation and structural characterization of perovskite-type La(x)Ln''1-xCoO3 by the thermal decomposition of heteronuclear complexes, La(x)Ln''(1-x) [Co(CN)(6)]center dot nH(2)O (Ln''=Sm and Ho)

Perovskite-type La(x)Ln''1-xCoO3 oxides are prepared by the thermal decomposition of La(x)Ln''(1-x) [Co(CN)(6)] . nH(2)O heteronuclear complexes. Except for LaCoO3 (hexagonal), the structures observed for LaxSm1-xCoO3 are orthorhombic. While the perovskite-type oxide HoCoO3 is not formed by decomposition at 1000 degrees C of the corresponding hexacyano complex, the partial replacing of Ho with La is effective in forming the perovskite-type oxide having an orthorhombic structure containing Ho even at 800 degrees C. A monotonous correlation (quasi-linear relationship) was found between the b- and c-lattice constants of the orthorhombic structures of the perovskite-type oxides and the effective radii of Ln ions, defined as r(eff) = xr(La) +(1-x)r(Ln''). The distortion parameter for the orthorhombic cell (3(0.5)a/b-1) increases with decrease in r(eff) and is expected to be 0.270 for perovskite-type HoCoO3. The crystal structure of the La(x)L(1-x)CoO(3) oxides is mainly controlled by the effective radii of Ln ions.