Preparation and crystal structure of new perovskite-type cobaltites R_1-xR'_xCoO₃

Chem. Met. Alloys 3 (2010) 184-190

https://doi.org/10.30970/cma3.0165

O. MYAKUSH, V. BEREZOVETS, A. SENYSHYN, L. VASYLECHKO

The crystal structures of new ternary oxides R_1‑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 La_1‑xPr_xCoO₃ (x ≤ 0.2) and La_1‑xNd_xCoO₃ (x ≤ 0.1) display a rhombohedral perovskite structure isotypic with NdAlO₃ (space group R‑3c). For La_1‑xPr_xCoO₃ (x ≥ 0.6), La_1‑xNd_xCoO₃ (x ≥ 0.5), Pr_1‑xNd_xCoO₃, Pr_1‑xSm_xCoO₃, and Nd_1‑xSm_xCoO₃ 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 PrCoO₃–NdCoO₃ system and possible formation of such solid solutions in the PrCoO₃–SmCoO₃ and NdCoO₃–SmCoO₃ systems. Two types of solid solution with rhombohedral and orthorhombic perovskite structures with an immiscibility gap between them have been confirmed in the LaCoO₃–PrCoO₃ and LaCoO₃–NdCoO₃ 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 La_0.9Nd_0.1CoO₃ (left) and Pr_0.8Sm_0.2CoO₃ (right)

Keywords

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