Dielectric characterisation of ceramics from the TiO2–TeO2 system

Abstract Compositions from TiO 2 –TeO 2 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 TiTe 3 O 8 . Single-phase TiTe 3 O 8 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 ( τ f ) of +133 ppm/°C, measured at ∼5 GHz. The concentration of structural defects in the TiTe 3 O 8 grains is negligible which makes the dielectric properties of TiTe 3 O 8 ceramics insensitive to variations in the heat-treatment conditions. The TiTe 3 O 8 compound is chemically compatible with TeO 2 , 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 TeO 2 ceramics with ∼ 20% porosity) and can be used for compensation of the temperature coefficient of resonant frequency of the TiTe 3 O 8 compound. Ceramics from the TiTe 3 O 8 –TeO 2 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 τ f , relative permittivity around 30 and a Q × f -value of ∼22,000 GHz suggests a potential for use in LTCC technology.