Structural investigation of the cubic perovskite-type doped lanthanum cobaltite La0.4Ba0.6CoO3−x

Abstract

Lanthanum strontium cobaltites, La0.4Ba0.6CoO3-x, which have a perovskite-type structure, are promising electrode materials for the doped lanthanum gallate electrolyte in solid oxide fuel cells (SOFCs). The purpose of the present study is to investigate the crystal structure of the cubic Pm-3m perovskite-type La0.4Ba0.6CoO3-x at room temperature and at high temperatures. La0.4Ba0.6CoO3-x pellets were supplied by Mitsubishi Materials Co., Tokyo, Japan. These pellets were used for roomtemperature and high-temperature neutron diffraction measurements. Neutron diffraction data were collected in air using HERMES [1], a diffractometer with a 150 multi-detector system, at room temperature and at high temperatures. The HERMES is installed at the JRR-3M reactor in Japan Atomic Energy Agency, Tokai, Japan. Neutrons with wavelength 1.8143 angstrom and 1.8207 angstrom were obtained by the (331) reflection of a Ge monochromator. A furnace with MoSi2 heaters [2] was placed on the sample table, and used for neutron diffraction measurements at high temperatures. The experimental data were analyzed assuming the cubic perovskite-type structure (space group Pm-3m) by Rietveld method with a computer program RIETAN-FP [3]. La and Ba atoms were placed at the special position 1b 1/2, 1/2, 1/2 of the Pm3m symmetry. Co andO atomswere placed at the 1a 0, 0, 0 and 3d 1/2, 0, 0 sites, respectively. The calculated profile agreed well with the observed one (Fig. 1). The refined crystal structure of La0.4Ba0.6CoO3-x is similar with that of La0.6Sr0.4CoO3-x reported in our previous work [4]. Analyeses of diffraction data obtained at high temperatures are now in progress.