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

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 (tans) and temperature coefficient (Delta epsilon'(T)/epsilon(RT)'). In this study, the HP-GDPs of Ga3+-Nb5+ co-doped TiO2 ceramics (GaNTO) have been achieved. The real part epsilon' of complex permittivity of GaNTO increased with increasing co-doping of Ga3+-Nb5+ ions, while tans was lower than 0.04. Interestingly, an excellent temperature coefficient (Delta epsilon'(T)/epsilon(RT)') was obtained over the temperature range from -60 to 220 degrees 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 epsilon' and Delta epsilon'(T)/epsilon' 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 similar to 1.9 to 11 M Omega. cm as the temperature decreased from 173 to 233 degrees C, while the grain capacitance remained constant at similar to 35 pF.cm(-1). However, epsilon' at low frequency decreased from similar to 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.