Microwave dielectric properties of Ba xLa 4Ti 3 + xO 12 + 3 x ( x = 0.0–1.0) ceramics

Abstract

In the BaO–La 2O 3–TiO 2 system, the Ba n La 4Ti 3 + n O 12 + 3 n homologous compounds exist on the tie line BaTiO 3–La 4Ti 3O 12 besides tungstenbronze-type like Ba 6 − 3 x R 8 + 2 x Ti 18O 54 (R = rare earth) solid solutions. There are four kinds of compounds in the homologous series: n = 0, La 4Ti 3O 12; n = 1, BaLa 4Ti 4O 15; n = 2, Ba 2La 4Ti 5O 18; n = 4, Ba 4La 4Ti 7O 24. 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 Ba x La 4Ti 3 + x O 12 + 3 x ceramics in the range of x between 0.2 and 1.0. With the increase in x, the dielectric constant ɛ r 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 τ f is improved from −17 to −12 ppm/°C. At x = 0.2, the ceramic composition obtained has dielectric constant ɛ r = 42, the temperature coefficient of the resonant frequency τ f = −17 ppm/°C and a high Q × f of 86,000 GHz.