Microwave dielectric characteristics of [(Mg_1−x−yCa_x)La_y](Ti_1−yAl_y)O₃ ceramic series

In this paper, [(Mg_1−x−yCa_x)La_y](Ti_1−yAl_y)O₃ (x + y = 0.75 and x = 0.79–0.89, y = 0.01) ceramics was prepared by the traditional solid-state reaction, moreover, the phase composition, microstructure and microwave dielectric properties of this ceramic series were investigated in detail. When x + y = 0.75, the main phase was CaTiO₃, and the impurity phases changed from MgAl₂O₄ to MgTi₂O₅ and MgTiO₃ as increasing the value of x. And, La³⁺ ions would enter the lattice point of these phases. The change of the apparent density was influenced much by the phase composition, but not the porosity. When increasing Ca content, the dielectric constant kept increasing and the temperature coefficient of dielectric constant (τ_ε) went down continuously. Meanwhile, the Q × f value showed the maximum value at x = 0.70, which was mainly determined by the pores and grain uniformity. The well sintered [(Mg_0.25Ca_0.70)La_0.05](Ti_0.95Al_0.05)O₃ ceramics showed microwave dielectric properties: ε_r = 84.7, Q × f = 133,700 GHz, τ_ε ≈ −841 ppm/°C. When a little of LaAlO₃ was added (y = 0.01), the more Ca content (x = 0.79–0.89) the sample had, the more columnar grains it showed, at the same time, the dielectric constant displayed a small increase, and the change of the temperature coefficient of dielectric constant (τ_ε) and Q × f value was small.