Very low dielectric loss and giant dielectric response with excellent temperature stability of Ga3+ and Ta5+ co-doped rutile-TiO2 ceramics

A newly discovered donor/acceptor co-doped rutile-TiO2 with an extremely high permittivity (epsilon') and low loss tangent (tan delta) has stimulated much research in capacitors and high-energy-density storage devices. However, poor high-temperature stability of epsilon' prevents its use in practical applications. Here, excellent dielectric properties with a very low tan delta approximate to 0.017-0.079 at 1 kHz, high epsilon' approximate to 5.5 x 10(3)-3.5 x 10(4) and good dielectric-temperature stability with a temperature coefficient, Delta epsilon'/(T)/epsilon'(RT) < +/- 15%, over a wide temperature range (e.g., Delta epsilon'(200 degrees C)/epsilon' (RT) = 6.26%) were simultaneously achieved in heat-treated Ga3+ and Ta6+ co-doped TiO2 (GTTO) ceramics. Both epsilon' and tan delta were nearly independent of DC bias up to 40 V. Notably, extremely large total-resistivity values of the insulating components were achieved (10(6)-10(10) Omega.cm) over the temperature range of 20-150 degrees C. These excellent electrical parameters are extremely hard to simultaneously realize in most giant dielectric materials. According to a first-principles study, there is a rather small coupling between 2Ta diamond and 2GaV(o) triangular shapes. Therefore, improvement of dielectric permittivity comes from insulating layers. Both the insulating grain boundaries and resistive thin outer-surface layers have remarkable influences on the high-performance giant dielectric properties of GTTO ceramics. (C) 2017 Elsevier Ltd. All rights reserved.