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 Qxf values decreased for dense TiO2 ceramics sintered from 1250 to 1500 degrees C, despite an increase in grain size. The main types of defects in TiO2 appeared to be defect dipoles [(Ti-T1') - (V-o(center dot center dot))] and oxygen vacancies (V-o(center dot center dot)), which were responsible for thermally-stimulated relaxations and dielectric loss at low and high frequencies. Interestingly, specimens sintered at 1250 degrees C exhibited a high temperature sensitivity of 2.12 MHz/degrees C (4.54-4.89 GHz) over a wide temperature range of -50 to 120 degrees C. With the advantages of high-epsilon(r) (105.2, 4.92 GHz) and high-Qxf (48 300 GHz), these TiO2 materials hold promise for use in wireless passive temperature sensing applications. (C) 2016 Elsevier Ltd. All rights reserved.