Influences of Ga3+ doping content on microstructure and interfacial polarization in colossal permittivity GayNb0.025Ti0.975-yO2 ceramics

Abstract

Colossal permittivity (CP) materials, particularly co–doped TiO2 ceramics, have garnered significant attention for their potential in high–performance ceramic capacitors. However, understanding the origin of CP remains a challenge, with the role of doping ratios between acceptor and donor ions largely underexplored. This study addresses this gap by systematically investigating the effects of Ga3+ concentrations on the microstructure and CP of GayNb0.025Ti0.975-yO2, prepared via the solid–state reaction method. The sintered ceramics exhibited a dense rutile TiO2 phase with increasing grain sizes and oxygen vacancies. Notably, CP values as high as 105 were achieved at Ga3+/Nb5+ ratio < 1.0. Optimal dielectric properties were observed at Ga3+/Nb5+ = 1.0, yielding a CP of 6.4 × 104 and a loss tangent < 0.03, surpassing the performance of many existing CP materials. Impedance spectroscopy revealed distinct electrical heterogeneity, with conductive grains and highly resistive grain boundaries with activation energies > 1.0 eV. Ceramics with 5% Ga3+ doping showed diminished CP due to the absence of semiconducting grains. The findings suggest that CP originates from the internal barrier layer capacitor. This study not only elucidates the crucial role of doping ratios in tailoring CP but also establishes a pathway for developing advanced dielectric materials with superior performance for ceramic capacitors.