Synthesis of SrLaAlO 4 fine ceramic powders by co-precipitation process
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Synthesis of SrLaAlO4 fine ceramic powders by co-precipitation process Xiang Nan Chen • Shu Ya Wu • Xiang Ming Chen
Received: 21 October 2012 / Accepted: 29 January 2013 / Published online: 27 February 2013 Ó Springer Science+Business Media New York 2013
Abstract SrLaAlO4 fine ceramic powders were synthesized by a co-precipitation process from the raw materials of La(NO3)36H2O (99 %), Al(NO3)39H2O (98–102 %) and SrCl26H2O (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: er = 19.5, Qf = 56,500 GHz, sf = -32.8 ppm/°C.
X. N. Chen S. Y. Wu (&) X. M. Chen Laboratory of Dielectric Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China e-mail: [email protected]
1 Introduction With the rapid development of microwave communication technologies, the microwave dielectric ceramics have receiving the increasing scientific and commercial interests because of their significant applications as microwave resonators, filters, oscillators and antennas [1–8]. The major property requirements for microwave dielectric ceramics include a high dielectric constant, low dielectric loss (high quality factor) and near-zero temperature coefficient of resonant frequency. The microwave dielectric characteristics are not only dependent on the composition and crystal structure but also significantly determined by the microstructure, and the homogenous microstructure is essential for achieving the best combination of microwave dielectric characteristics especially the ultra-low dielectric loss (ultra-high qualify factor). Recently, the microwave dielectric ceramics with ultralow dielectric loss have been proposed and developed in the MRAlO4 systems (M = Sr and Ca; R = La, Nd, Sm and Y) [9–13]. Among these materials, SrLaAlO4 has the highest quality factor Q, and the predicted Qf value (f is the resonant fre
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