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. Ca ₅ Nb ₄ TiO ₁₇ ceramics had a relative permittivity, ^ε _r = 44.9 (porosity corrected value 49.4), quality factor, Q _u × f = 17,600 GHz (at 4.13 GHz) and temperature coefficient of resonant frequency, τ _f = −112.9 ppm °C ⁻¹ , whereas for Ca ₅ Ta ₄ TiO ₁₇ , 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 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.