Microwave dielectric ceramics of hexagonal (Ba1-xAx)La4Ti4O15 (A = Sr, Ca) for base station applications

Microwave dielectric ceramics with composition of (Ba1-xSrx)La4Ti4O15 (BSLT) and (Ba1-xCax)La4Ti4O15 (BCLT) were prepared by a conventional solid-state reaction method. Hexagonal structures were observed for all compositions, and the shift of reflection peaks in XRD patterns implies the variation of the lattice parameters and the formation of solid solutions. The substitution of Sr for Ba in this system lowered the sintering temperature to a certain extent, whereas the Ca-substituted counterparts did not alter their sintering temperatures. The microstructure of all well-sintered ceramics exhibits minimal porosity and is comprised of uniform, platelet-shaped grains. The dielectric constant and temperature coefficient of resonant frequency for samples with maximum densities are in the range of 45-49 and -3-10 ppm/ deg C, and they do not change much with compositions for both BSLT and BCLT ceramics. However, Q X f value significantly increases from 25,000 to 53,000 GHz with increasing Sr content, whereas it does not markedly alter with increasing Ca content. Both of them are potential candidates for base station resonator applications.