Dielectric characterisation of ceramics from the TiO2–TeO2 system

Compositions from TiO2–TeO2 tie line were characterised using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and dilatometry. Results show that the only binary compound existing on the tie line is TiTe3O8. Single-phase TiTe3O8 was synthesised at 700°C in air and sintered at 720°C to ∼95% of theoretical density. Such ceramics exhibit a relative permittivity of 50, a Q×f-value of 30,600 GHz and a temperature coefficient of resonant frequency (τf) of +133 ppm/°C, measured at ∼5 GHz. The concentration of structural defects in the TiTe3O8 grains is negligible which makes the dielectric properties of TiTe3O8 ceramics insensitive to variations in the heat-treatment conditions. The TiTe3O8 compound is chemically compatible with TeO2, which displays a negative temperature coefficient of resonant frequency (a relative permittivity of 19.3, a Q×f-value of 30,000 GHz and a temperature coefficient of resonant frequency of −119 ppm/°C for TeO2 ceramics with ∼ 20% porosity) and can be used for compensation of the temperature coefficient of resonant frequency of the TiTe3O8 compound. Ceramics from the TiTe3O8–TeO2 subsystem can be sintered to >97% of theoretical density at temperatures as low as 670°C, which together with the fact that the ceramics exhibit a highly tunable τf, relative permittivity around 30 and a Q×f-value of ∼22,000 GHz suggests a potential for use in LTCC technology.