Sintering temperature-induced structural transition in LaCrO3-based conducting oxides synthesized from nano-powders

Preparation condition plays a critical role in the structure and properties of ceramics. However, exactly how it affects lanthanum chromate (LaCrO3)-based conducting oxides remains poorly understood. In this work, the effects of sintering temperature on the crystal structure, microstructure, and electrical conductivity of pure and Sr2+-/Ca2+-substituted LaCrO3 ceramics have been investigated. It is found that the calcining temperature can be reduced by 200-300 K to obtain a single-perovskite structure by using nano-powders as raw materials. A sintering temperature-induced structural transition from orthorhombic Pbnm phase to rhombohedral R3 over bar c$R\bar 3c$ phase is found in La0.8Sr0.2CrO3, and the possible mechanism is attributed to a thermally induced transformation of the thermodynamic metastable orthorhombic to stable rhombohedral phase after thermal treatment at higher temperatures. The electrical conductivity in a broad temperature range (from room temperature up to 1923 K) is measured. The conductivity increases with the elevated sintering temperature and soaking time, and it shows a remarkable enhancement by introducing the Sr and Ca ions. These results suggest that the sintering temperature should be well controlled and optimized to obtain desired crystal structure and electrical conductivity in LaCrO3-based materials for various applications.