Giant dielectric properties of Ga3+–Nb5+Co-doped TiO2 ceramics driven by the internal barrier layer capacitor effect

Abstract

The high-performance giant dielectric properties (HP-GDPs) of materials have been continuously investigated due to their significant potential for many applications such as ceramic capacitors and energy storage devices. Unfortunately, it has been difficult to achieve low values for both loss tangent (tanδ) and temperature coefficient (Δε′(T)/ε′RT). In this study, the HP-GDPs of Ga3+–Nb5+ co-doped TiO2 ceramics (GaNTO) have been achieved. The real part ε′ of complex permittivity of GaNTO increased with increasing co-doping of Ga3+–Nb5+ ions, while tanδ was lower than 0.04. Interestingly, an excellent temperature coefficient (Δε′(T)/ε′RT) was obtained over the temperature range from −60 to 220 °C with less than ±15% variation, meeting the basic requirement for fabricating ultra-stable X9R type (EIA code) capacitors. The sintered ceramics were systematically characterized. The mean grain size slightly decreased with increasing co-doping concentration, while the ε′ and Δε′(T)/ε′ values significantly improved. High-resolution transmission electron microscopy revealed Nb/O-rich and Ti-deficient grains at the grain boundary (GB), while all elements were homogeneously dispersed inside the grain area. The grain resistance significantly increased from ~1.9 to 11 MΩ. cm as the temperature decreased from 173 to 233 °C, while the grain capacitance remained constant at ~35 pF.cm−1. However, ε′ at low frequency decreased from ~6000 to 210. According to the results of broadband dielectric spectroscopy indicate that the HP-GDPs of GaNTO primarily would result from the internal barrier layer capacitor (IBLC) effect related to a formation of a Schottky barrier for segregation of the dopant at the GB.