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 electro n microscopy (TEM) and dilatometry. Results show that the only binary compo und existing on the tie line is TiTe3O8, Single-phase TiTe3O8 was synthesis ed at 700 degreesC in air and sintered at 720 degreesC to similar to 95% of theoretical density. Such ceramics exhibit a relative permittivity of 50, a Oxf-value of 30,600 GHz and a temperature coefficient of resonant frequen cy (tau (f)) of +133 ppm/degreesC, measured at similar to5 GHz. The concent ration of structural defects in the TiTe3O8 grains is negligible which make s the dielectric properties of TiTe3O8 ceramics insensitive to variations i n the heat-treatment conditions. The TiTe3O8 compound is chemically compati ble with TeO2, which displays a negative temperature coefficient of resonan t frequency (a relative permittivity of 19.3, a Qxf-value of 30,000 GHz and a temperature coefficient of resonant frequency of -119 ppm/degreesC for T eO2 ceramics with similar to 20% porosity) and can be used for compensation of the temperature coefficient of resonant frequency of the TiTe3O8 compou nd. Ceramics from the TiTe3O8-TeO2 subsystem can be sintered to > 97% of th eoretical density at temperatures as low as 670 degreesC, which together wi th the fact that the ceramics exhibit a highly tunable rf, relative permitt ivity around 30 and a Qxf-value of similar to 22,000 GHz suggests a potenti al for use in LTCC technology. (C) 2001 Elsevier Science Ltd. All rights re served.