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

In the BaO-La2O3-TiO2 system, the BanLa4Ti3+O-n(12+3n) homologous compounds exist on the tie line BaTiO3-LaJi(3)O(12) 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 8, locates around 45, the quality factor Q x 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 tau(f) is improved from -17 to -12 ppm/degrees C. At x = 0.2, the ceramic composition obtained has dielectric constant epsilon(r) = 42, the temperature coefficient of the resonant frequency tau(f) = -17 ppm/degrees C and a high Q x f of 86,000 GHz. (c) 2005 Elsevier Ltd. All rights reserved.