Synthesis of SrLaAlO₄ fine ceramic powders by co-precipitation process

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: ε _r  = 19.5, Qf = 56,500 GHz, τ _f  = −32.8 ppm/°C.