Hydrothermal synthesis of perovskite strontium doped lanthanum chromite fine powders and its sintering

Abstract

Sr doped lanthanum chromite powders with two different compositions, La 0.9Sr 0.1CrO 3 and La 0.8Sr 0.2CrO 3, were prepared from precursor lanthanum chromite gels obtained by the coprecipitation method, followed by hydrothermal treatments at temperatures from 400 to 450 °C, for various reaction times varying from 0.5 to 2 h. The reaction products were characterized by XRD, SEM and TEM techniques. The powder was cold isostatically pressed at 200 MPa, and then sintered in air at 1500 °C for several intervals (1–20 h). Relative density measurements were conducted by helium pycnometry and the microstructure was revealed by SEM after thermal etching. The X-ray diffraction patterns of the powders corresponding to La 0.9Sr 0.1CrO 3 and La 0.8Sr 0.2CrO 3 nominal compositions obtained at 400 and 425 °C for 1 h, respectively, were indexed with that of the orthorhombic single LaCrO 3 phase. SEM and TEM micrographs showed that the particles had irregular peanut-like morphology, and the average particle size was 300 nm. Furthermore, the maximum relative density of the La 0.8Sr 0.2CrO 3 sample obtained by the heat treatment in air at 1500 °C for 20 h was 97% of the theoretical density and the average grain size of the sintered pellet was of 5 μm. The electric conductivity and activation energy determined for this pellet were 14477.3 S m −1 and 0.13 eV, respectively.