Very low dielectric loss and giant dielectric response with excellent temperature stability of Ga 3+ and Ta 5+ co-doped rutile-TiO 2 ceramics

A newly discovered donor/acceptor co-doped rutile-TiO2 with an extremely high permittivity (ε′) and low loss tangent (tanδ) has stimulated much research in capacitors and high-energy-density storage devices. However, poor high-temperature stability of ε′ prevents its use in practical applications. Here, excellent dielectric properties with a very low tanδ ≈ 0.017–0.079 at 1 kHz, high ε′ ≈ 5.5 × 103–3.5 × 104 and good dielectric-temperature stability with a temperature coefficient, Δε′(T)/ε′RT < ± 15%, over a wide temperature range (e.g., Δε′(200 °C)/ε′RT = 6.26%) were simultaneously achieved in heat-treated Ga3 + and Ta5 + co-doped TiO2 (GTTO) ceramics. Both ε′ and tanδ were nearly independent of DC bias up to 40 V. Notably, extremely large total-resistivity values of the insulating components were achieved (106–1010 Ω·cm) over the temperature range of 20–150 °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 2GaVo 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.