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

Sr doped lanthanum chromite powders with two different compositions, La0.9Sr0.1CrO3 and La0.8Sr0.2CrO3, 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 La0.9Sr0.1CrO3 and La0.8Sr0.2CrO3 nominal compositions obtained at 400 and 425 °C for 1 h, respectively, were indexed with that of the orthorhombic single LaCrO3 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 La0.8Sr0.2CrO3 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.