Structural and electrical properties of cobalt-doped 4H- $\mathrm{SrMnO}_{3-\delta}$ SrMnO 3 - δ perovskites obtained by the hydrothermal method

Abstract

A mild hydrothermal method was adapted to prepare the $ \mathrm{SrMn}_{1-x}\mathrm{Co}_{x}\mathrm{O}_{3-\delta}$ ( $0 \le x \le 0.2$ ) compounds. They showed hexagonal-4H perovskite-type structure with space group $P6_{3}/mmc$ , and cell parameters $a \sim 5.45$ and $c \sim 9.08$ A, as deduced from X-ray and neutron diffraction data. The mean atomic concentrations indicated global stoichiometries close to the nominal ones whereas electron microscopy analyses pointed out to heterogeneity at the nanoscale. The characterization of the electrical response by means of impedance measurements, suggested a semiconductor behavior mainly ascribed to bulk contributions. Relaxation and conduction processes were analyzed. The materials showed mixed electronic-ionic conduction above $\sim 400$ K, when ionic conduction between intergrains becomes favored. Microstructural homogeneity was revealed as the key factor controlling the electrical response.