Effect of synthetic route on sintering behaviour, phase purity and conductivity of Sr- and Mg-doped LaGaO₃ perovskites

La_1-xSr_xGa_1-yMg_yO_3-δ (LSGM) powders containing different amounts of Sr²⁺ and Mg²⁺ were prepared from precursors synthesised by either Pechini or citrate sol-gel method and by subsequent calcination at 1400 °C. Some powders were also submitted to further 10 h firing at 1500 °C. All as-calcined powders contained small amounts of Sr- and Ga-containing phases (namely SrLaGa₃O₇ and SrLaGaO₄), as detected by X-Ray Diffraction (XRD). The relative amounts of these phases depended on x and y, i.e. the dopants' levels. Nevertheless, powders prepared by the citrate method exhibited systematically higher phase purity than those obtained by the Pechini process. Calcined powders were then sintered at 1500 °C (10 h) in air and the degree of sintering was assessed by scanning electron microscopy (SEM). Phase composition of sintered pellets was different from that of powders. In fact, sintered pellets showed the presence of MgO, as detected by SEM, and of lesser amounts of SrLaGa₃O₇. Both these phases were less abundant in materials sintered using powders prepared by citrate method, thus suggesting that Pechini method does not represent the best wet chemical process for manufacturing. The conductivity of sintered pellets was measured by impedance spectroscopy in the 600-800 °C interval. Conductivity values of LSGM materials were affected by secondary phase segregation and, therefore, depended on both composition and sol-gel method synthetic route.