Structure and microwave dielectric properties of Ca5A4TiO17 (A = Nb, Ta) ceramics

Ca(5)A(4)TiO(17) (A = Nb, Ta) dielectric ceramics were prepared by the conventional solid-state ceramic route. The structure and microstructure of the ceramics were investigated by X-ray diffraction, transmission electron microscopy and scanning electron microscopic techniques. The electron diffraction patterns of Ca(5)A(4)TiO(17) were indexed according to the model in P2(1)/c. The microwave dielectric properties of the sintered ceramics were measured in the frequency range of 3-6 GHz. Ca5Nb4TiO17 ceramics had a relative permittivity, epsilon(r) = 44.9 (porosity corrected value 49.4), quality factor, Q(u) x f = 17,600 GHz (at 4.13 GHz) and temperature coefficient of resonant frequency, iota(f) = -112.9 ppm degrees C-1, whereas for Ca5Ta4TiO17, the obtained values were 40.1 (porosity corrected value 44.1), 16,450 GHz (at 4.22 GHz) and -53.6 ppm degrees C-1, respectively. The density of Ca(5)A(4)TiO(17) ceramics was increased by adding small amounts of zinc borosilicate (60ZnO-30B(2)O(3)-10SiO(2)) glass. The effect of glass addition on the microwave dielectric properties of Ca(5)A(4)TiO(17) ceramics was also investigated. (C) 2010 Elsevier B.V. All rights reserved.