Preparation and crystal structure of new perovskite-type cobaltites R1-xR'xCoO3


Chem. Met. Alloys 3 (2010) 184-190




The crystal structures of new ternary oxides R1‑xR'xCoO3 (R, R'=La, Pr, Nd, Sm), obtained by solid-state reaction in air at 1200ºC, have been studied by X-ray powder diffraction, using conventional laboratory and synchrotron radiation sources. It was established that at ambient conditions La1‑xPrxCoO3 (x  0.2) and La1‑xNdxCoO3 (x  0.1) display a rhombohedral perovskite structure isotypic with NdAlO3 (space group R‑3c). For La1‑xPrxCoO3 (x  0.6), La1‑xNdxCoO3 (x  0.5), Pr1‑xNdxCoO3, Pr1‑xSmxCoO3, and Nd1‑xSmxCoO3 the orthorhombic GdFeO3 type of structure (space group Pbnm) is inherent. The obtained structural data indicate the existence of a continuous solid solution with orthorhombic perovskite structure in the PrCoO3NdCoO3 system and possible formation of such solid solutions in the PrCoO3SmCoO3 and NdCoO3SmCoO3 systems. Two types of solid solution with rhombohedral and orthorhombic perovskite structures with an immiscibility gap between them have been confirmed in the LaCoO3PrCoO3 and LaCoO3NdCoO3 systems. The ranges of existence of these solid solutions have been determined.



Projection of the unit cell and packing of CoO6 octahedra in the structures of La0.9Nd0.1CoO3 (left) and Pr0.8Sm0.2CoO3 (right)



Cobaltites / Crystal structure / X-ray powder diffraction / Perovskite