Low loss tangent and excellent humidity–temperature stability with DC bias independence of giant-permittivity TiO2 doped with indium tin oxide and tantalum pentoxide

Abstract

Although a high permittivity (ε′>104) of rutile TiO2 can easily be obtained by doping with Ta5+, the low loss tangent (tanδ<0.05) cannot be achieved. Furthermore, ε′ of giant dielectric oxides is usually dependent on environmental factors (temperature and humidity) and operation factors (frequency and DC bias). In this study, greatly reduced tanδ and enhanced ε′–stabilities were obtained in TiO2 by doping with Ta2O5 and indium tin oxides (ISO). Dense ceramics with homogeneously dispersion of doping elements were obtained by sintering at 1400 °C for 3 h. The rutile phase was detected with expanded lattice parameters as ISO increased, while the average grain size decreased slightly with a narrow size distribution. According to the Raman spectroscopy, oxygen vacancies in Ta2O5–doped TiO2 tended to slightly increase by doping with ISO. Besides a high ε′ of ∼2–4 × 104, low tanδ values of 0.007–0.04 (103 Hz) were achieved in the temperature range of −80 to 200 °C. The temperature coefficient of ε′ at 1 kHz from −120 to 200 °C was lower than ±10% compared to that of 25 °C. Furthermore, the ε′ was also nearly independent on the DC bias even at 300 V/cm (∼2.6%). Surprisingly, the ε′ was nearly independent on humidity over the range of 25–90%RH. Thereas, this giant dielectric material may have a great potential for capacitor applications. Impedance and dielectric spectroscopies revealed that the giant dielectric properties were caused by the interfacial polarization, while the effect of defect dipoles cannot be ignored, which could have a primary contribution in a low–temperature range.