Re-estimation of Maxwell-Wagner relaxation for novel absorbers via (Ta+Ga)-doped rutile-type TiO2 ceramics with various valence proportions and sintering temperatures

Abstract

To realize next-generation capacitor materials with novel absorption properties under unconventionally severe conditions, the present study estimates the Maxwell-Wagner relaxation via investigation on (Ta+Ga) co-doped rutile-type TiO2 ceramics with changing the nominal proportions of penta-/tri-valent dopants and sintering temperatures. The key roles of Ta and Ga on resistivities in grains and grain boundaries are clarified by carefully discussing the temperature- and frequency-dependence of permittivity, Cole-Cole plots, and activation energies. It is deduced that a mean free path of charge carriers in grains is longer for a Ta-doped sample than (Ta+Ga) co-doped ones, while Ga-rich samples are more resistive. High-temperature sintering tends to result in less resistive samples due to the generation of oxygen vacancies or more active donor-like defects like Ta5+ and Ti3+ ions. For ideal Maxwell-Wagner properties on rutile-type TiO2, it is promising to optimize the conductive-core/insulative-shell structure by manufacturing Ta-rich grains and Ga-rich grain boundaries with low-temperature sintering.