Synthesis of SrLaAlO4 fine ceramic powders by co-precipitation process

Abstract

SrLaAlO4 fine ceramic powders were synthesized by a co-precipitation process from the raw materials of La(NO3)3·6H2O (99 %), Al(NO3)3·9H2O (98–102 %) and SrCl2·6H2O (99 %). Effects of the precipitating pH value and thermal treatment temperature upon the phase constitution and microstructures of the product powders were determined together with the reaction mechanisms. The precipitating pH value indicated a key role dominating the reaction process. For the situation of precipitating pH = 7, SrLaAlO4 phase began to form around 900 °C and became the major phase above 1,000 °C where small amount of secondary phases of La2O3, LaSrAl3O7, La10Al4O21 were detected. With increasing the precipitating pH value to 8 and 9, SrLaAlO4 major phase were obtained at 900 °C together with small amount of secondary phases of La2O3, LaSrAl3O7 and La(OH)3, and the amount of secondary phases decreased with increasing thermal treatment temperature. The grain morphology of the product powders was also determined by the precipitating pH value and the thermal treatment temperature. SrLaAlO4 fine ceramic powders with homogenous morphology and less secondary phases were obtained by heating the precursors with precipitating pH = 9 at 900 and 1,000 °C in air for 10 h. Densification of SrLaAlO4 ceramics derived from the present powders could be achieved at 1,450 °C, and the optimal microwave dielectric properties were obtained as: e r = 19.5, Qf = 56,500 GHz, τ f = −32.8 ppm/°C.