General properties of polycrystalline LnNiO(3) (Ln = Pr, Nd, Sm) compoundsprepared through different precursors

We report on the synthesis and general physical properties of polycrystalli ne samples of LnNiO(3) (Ln = Pr, Nd, Sm), These compounds crystallize in a GdFeO3-type orthorhombically distorted perovskite structure, Pbnm space gro up symmetry, and reveal a first-order metal-insulator transition in a large range of temperatures varying from similar to 130 to 400 K. The samples we re prepared through three different methods: (1) the conventional ceramic p rocess by mixing and reacting simple oxides; (2) through precipitation of h ydroxides of Ln(3+) and Ni3+ and (3) through sol-gel precursors. The sample s were subjected to heat treatments at temperatures up to 1000 degrees C an d under oxygen pressures as high as 70 bar. Observations of the microstruct ure and measurements of X-ray powder diffraction XRD, electrical resistivit y rho(T), and differential scanning calorimetric DSC, indicated important e ffects that precursors from different methods have upon the final propertie s of these compounds. A comparison between these characterizations revealed that sol-gel precursors resulted in better quality samples of LnNiO(3) com pounds. (C) 2000 Academic Press.