Synthesis Of NdAlO₃and SrLaAlO₄Microwave Dielectric Ceramics Via Co-precipitation Process

and SrLaAlO4microwave dielectric ceramics were prepared by co-precipitation process, and the structures and properties of NdAlO3and SrLaAlO4ceramics are evaluated. Their formation process and the influence of synthesis process conditions on their microwave dielectric properties are discussed in this paper. Main conclusions obtained are as follows:NdAlO3fine ceramic powders were successfully synthesized by co-precipitation method using aqueous ammonia as precipitating agent. NdAlO3single phase forms heat treated at800℃with a process that aqueous ammonia and0.25～1mol/L of nitrate solution in proportion mix gradually and precipitating pH values keep8～9. Uniform and spherical particles of product powder are obtained, the average particle size decreases slightly with nitrate solution concentration increasing, and the smallest average particle size is about60nm. While aqueous ammonia dropped into nitrate solution, NdAlO3phase forms at800℃with trace Nd4Al2O9phase and average particle size is about100nm. NdAlO3ceramics were prepared using NdAlO3fine powders synthesized above. NdAlO3ceramics which were prepared in a process aqueous ammonia and1mol/L of nitrate solution in proportion mixed gradually and then adjusted pH values to8.5perform the best microwave dielectric properties of all NdAlO3ceramics:Qf=115,800GHz, εr=21.4,τf=-47.2ppm/℃. In three process factors including mixing sequence of precipitating agent and nitrate solution, precipitating pH values and concentration of nitrate solution we discuss, precipitating pH value seems to be the principal factor.SrLaAlO4fine 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. The grain morphology of the product powders was also determined by the precipitating pH value and the thermal treatment temperature. SrLaAlO4fine ceramic powders with homogenous morphology and less secondary phases were obtained by heating the precursors with precipitating pH=9at900and1000℃in air for10h. SrLaAlO4ceramics prepared on the condition of precipitating pH value keeping8and9form a tetragonal K.2NiF4-type SrLaAlO4single phase with a relatively high density. In the ceramic samples prepared with a precipitating pH value7, pianissimo secondary phase peaks of SrLaAl3O7are observed, and density is lower than the formers. When precipitating pH value keeps8, SrLaAlO4ceramic samples sintered at1425℃perform optimal microwave dielectric properties:εr=19.5, Qf=56,500GHz, τf=-32.8ppm/℃. While precipitating pH value keeps7, Qf value of SrLaAlO4ceramic samples is lower because trace amount of the secondary phase existing in ceramics and lower density cause larger extrinsic loss.