Large-size-mismatch co-dopants for colossal permittivity rutile TiO2 ceramics with temperature stability

Colossal permittivity (CP) in donor-accepter co-doped rutile TiO2 has attracted significant interest. Here, the CP behavior of (Ta + La) co-doped rutile TiO2 ceramics were studied, where the ionic radii of Ta5+ and La3+ are much larger than that of Ti4+. The ceramics with an extremely low doping exhibit colossal dielectric permittivity (∼2.6 × 104) with an acceptable low dielectric loss (<0.07) in the frequency range from 40 to 106 Hz. The CP properties obtained in (Ta + La) co-doped TiO2 ceramics show excellent temperature stability over a wide temperature range of 20-400 °C. The X-ray diffraction analysis and the density functional theory calculation illustrates that the La23+Vo
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- Ti23+ and Ta25+Ti3+Ti4+ defect complexes with the lowest energy are responsible for the enhanced dielectric properties. Moreover, the defect complex formed by large-size trivalent substitutions and oxygen vacancy is very stable, and assists in improving temperature stability of the dielectric properties of co-doped rutile TiO2 ceramics.