Structure and Microwave Dielectric Properties of Ca5A4TiO17 (A = Nb, Ta) Ceramics

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Ca5A4TiO17 (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 Ca5A4TiO17 were indexed according to the model in P21/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, εr = 44.9 (porosity corrected value 49.4), quality factor, Qu × f = 17,600 GHz (at 4.13 GHz) and temperature coefficient of resonant frequency, τf = −112.9 ppm °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 °C−1, respectively. The density of Ca5A4TiO17 ceramics was increased by adding small amounts of zinc borosilicate (60ZnO–30B2O3–10SiO2) glass. The effect of glass addition on the microwave dielectric properties of Ca5A4TiO17 ceramics was also investigated.