Ba2ZnSi2O7基低介微波介质陶瓷的谐振频率温度系数调控机制研究

The low-permittivity microwave dielectric ceramics (εr<15) exhibit a typically high-magnitude negative temperature coefficient of resonant frequency (τf) lower than -70ppm/°C according to the εr–τf relationship. Generally, the temperature-compensated dopants with a large positive τf value, such as TiO2, CaTiO3, and SrTiO3, are utilized to control the τf value of low-permittivity microwave dielectric ceramics as the conventional processes, however, this measure will occasionally encounter difficulties. Therefore, novel Ba2ZnSi2O7 low-permittivity microwave dielectric ceramics with weak ferroelectricity will be investigated to achieve a near-zero τf value by changing sintering atmosphere, Zn2+ content and Ba/Si ratio, which will lead to variation of crystal structure, position shift and strength change of the εr anomaly peaks. The coexistence of weak ferroelectricity and low-permittivity microwave dielectric properties will be focused by our attentions, and their evidences and forming mechanisms will be studied in detail. Furthermore, charge compensation mechanisms, shifting and expanding mechanisms of εr anomaly peaks and their effects on the τf value will be investigated deeply. Finally, a novel τf controlling mechanism by adjusting their own crystal structure will be achieved in low-permittivity microwave dielectric ceramics.

根据谐振频率温度系数(τf)与介电常数(εr)之间的关系式可知，典型的低介微波介质陶瓷(εr<15)的τf值约为-70ppm/°C以下，通常需要掺入TiO2、CaTiO3和SrTiO3等正τf值添加剂与之复合达到调控τf值至近零的目的，但这种调控方式在某些环境下会遇到困难。为此，本项目拟以低介Ba2ZnSi2O7微波介质陶瓷为研究对象，利用其弱铁电性特性，通过改变烧结气氛、Zn2+含量和Ba/Si比值来调节材料晶体结构和介温曲线上介电常数异常峰的位置和强度，达到控制τf值至近零的目的。在此过程中，重点关注其中出现的弱铁电性和低介微波介电性能共存现象，探寻弱铁电性证据和形成机制，深入研究离子电价平衡补偿机制、介温曲线峰值(不一定是居里峰)的移峰和展宽机制及其对τf值的影响规律，最终获得一种通过自身晶格结构调节来调控低介微波介质陶瓷τf值的新机制。

随着通信设备运行频率的不断提高，信号延迟现象会变得更加明显，系统损耗和发热量也会随之增大，系统稳定性会逐渐变差。传统Ti4+基正τf值调控剂在抗还原特性及化学相容性等方面存在诸多不足之处，因此寻找一种新型温频特性调控方法十分必要。本项目紧紧围绕钡锌硅基陶瓷展开，系统地研究其物相演变、结构调控、化学缺陷、介电（铁电）特性，得到了系列具有优异微波介电性能的材料。其中 BaSiO3、Ba2ZnSi2O7、BaZnSiO4 和BaZnSi3O8陶瓷均存在较弱的铁电性，而Ba5Si8O21低介微波介质陶瓷具有反常的正τf值，有可能成为新型的温频特性调节剂。Ba2Zn(1+x)Si(2+y)O(7+x+2y)(x=-1，y=0、1.0、1.2、2.0)陶瓷在还原性气氛中均具有良好的低介微波介电性能和稳定的相成分，有望应用于高频、高精度 BME-MLCC领域。