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

Publication date: 5 June 2017
Source:Materials & Design, Volume 123
Author(s): Wattana Tuichai, Nateeporn Thongyong, Supamas Danwittayakul, Narong Chanlek, Pornjuk Srepusharawoot, Prasit Thongbai, Santi Maensiri
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 1kHz, 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 40V. Notably, extremely large total-resistivity values of the insulating components were achieved (10⁶–10¹⁰Ω·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.

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