Al^3+置换对Ba4Pr28/3Ti18-yAl4y/3O54陶瓷晶体结构与微波介电性能的影响

Effect of Al^3+Substitution on Crystal Structure and Microwave Dielectric Properties of Ba4Pr28/3Ti18-yAl4y/3O54 Ceramics

通过标准固相法制备了Ba4Pr28/3Ti18-yAl4y/3O54(0≤y≤2)微波介质陶瓷,结合X射线衍射(XRD)、背散射(BSE)以及X射线能谱(EDS)研究了Al^3+置换对其晶体结构、微观形貌以及微波介电性能的影响。XRD分析表明,样品的主晶相均为正交钨青铜结构,晶胞参数及晶胞体积随Al^3+置换量的增大先减小后增大。BSE及EDS分析表明,当0≤y≤1.5时为单相结构,而当y=2.0时出现了少量第二相;晶粒尺寸和柱状晶粒的长度随Al3+置换量的增大略有减小。Al^3+置换能有效提升Ba4Pr28/3Ti18-yAl4y/3O54陶瓷的品质因数(Q×f),降低谐振频率温度系数(TCF),但介电常数(εr)减小。当y=1.5时,Ba4Pr28/3Ti18-yAl4y/3O54陶瓷具有较好的微波介电性能,εr=76.6,Q×f=10800 GHz,TCF=+55 ppm/℃。

Ba4Pr28/3Ti18-yAl4y/3O54(0≤y≤2) microwave dielectric ceramics were prepared by using the standard solid-state reaction method. The effect of Al3+ substitution on phase composition, microstructure and microwave dielectric properties was studied by using X-ray diffraction(XRD), back-scattering(BSE) and X-ray energy spectrometer(EDS). It is found that all the samples were of orthogonal tungsten-bronze structure as the major phase. The unit cell parameters and unit cell volume were decreased first and then increased with increasing substitution content of Al3+. According to the BSE and EDS results, single-phase structure was observed in the samples with 0≤y≤1.5, while a trace of second phase was present in the one with y = 2.0. The grain size and the length of the columnar grains were decreased as the content of Al3+ was increased. Al3+ substitution could effectively improve the quality factor(Q× f) and reduce the temperature coefficient of resonance frequency(TCF), but decrease the dielectric constant( εr). Specifically, the Ba4Pr28/3Ti18-yAl4y/3O54 ceramics with y = 1.5 exhibited optimal microwave dielectric properties, with εr = 76.6, Q× f = 10800 GHz and TCF = +55 ppm/℃.