Microwave dielectric properties of BaxLa4Ti3 + xO12 + 3x (x = 0.0–1.0) ceramics

In the BaO–La2O3–TiO2 system, the BanLa4Ti3 + nO12 + 3n homologous compounds exist on the tie line BaTiO3–La4Ti3O12 besides tungstenbronze-type like Ba6 − 3xR8 + 2xTi18O54 (R = rare earth) solid solutions. There are four kinds of compounds in the homologous series: n = 0, La4Ti3O12; n = 1, BaLa4Ti4O15; n = 2, Ba2La4Ti5O18; n = 4, Ba4La4Ti7O24. These compounds have the layered hexagonal perovskite-like structure, which has a common sub-structure in the crystal structure. These compounds have been investigated in our previous studies. In this study, we have investigated the phase relation and the microwave dielectric properties of BaxLa4Ti3 + xO12 + 3x ceramics in the range of x between 0.2 and 1.0. With the increase in x, the dielectric constant ɛr locates around 45, the quality factor Q × f shows over 80,000 GHz at x = 0.2 and the minimum value of 30,000 GHz at x = 0.9, and the temperature coefficients of resonant frequency τf is improved from −17 to −12 ppm/°C. At x = 0.2, the ceramic composition obtained has dielectric constant ɛr = 42, the temperature coefficient of the resonant frequency τf = −17 ppm/°C and a high Q × f of 86,000 GHz.