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

Abstract

The crystal structures of new ternary oxides R 1-x R' x CoO 3 (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 La 1-x Pr x CoO 3 (x ≤ 0.2) and La 1-x Nd x CoO 3 (x ≤ 0.1) display a rhombohedral perovskite structure isotypic with NdAlO 3 (space group R-3c). For La 1-x Pr x CoO 3 (x ≥ 0.6), La 1-x Nd x CoO 3 (x ≥ 0.5), Pr 1-x Nd x CoO 3 , Pr 1-x Sm x CoO 3 , and Nd 1-x Sm x CoO 3 the orthorhombic GdFeO 3 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 PrCoO 3-NdCoO 3 system and possible formation of such solid solutions in the PrCoO 3-SmCoO 3 and NdCoO 3-SmCoO 3 systems. Two types of solid solution with rhombohedral and orthorhombic perovskite structures with an immiscibility gap between them have been confirmed in the LaCoO 3-PrCoO 3 and LaCoO 3-NdCoO 3 systems. The ranges of existence of these solid solutions have been determined. Cobaltites / Crystal structure / X-ray powder diffraction / Perovskite