Temperature-dependent dielectric properties, thermally-stimulated relaxations and defect-property correlations of TiO2 ceramics for wireless passive temperature sensing

We prepared TiO2 ceramics by conventional solid-state reaction process and systematically characterized their temperature-dependent dielectric properties over wide ranges of frequency and temperature. The dielectric-temperature spectra and thermally stimulated depolarization currents in TiO2 revealed significant thermally-stimulated relaxations. At microwave frequencies, the Q × f values decreased for dense TiO2 ceramics sintered from 1250 to 1500 °C, despite an increase in grain size. The main types of defects in TiO2 appeared to be defect dipoles [(TiTi′)−(VO••)] and oxygen vacancies (VO••), which were responsible for thermally-stimulated relaxations and dielectric loss at low and high frequencies. Interestingly, specimens sintered at 1250 °C exhibited a high temperature sensitivity of 2.12 MHz/°C (4.54–4.89 GHz) over a wide temperature range of −50 to 120 °C. With the advantages of high-εr (105.2, 4.92 GHz) and high-Q × f (48 300 GHz), these TiO2 materials hold promise for use in wireless passive temperature sensing applications.