Triple-doping of (Ga1/2Nb1/2)xTi1-xO2 ceramics with Al3+ for enhanced giant dielectric response with simultaneous decrease in dielectric loss

Abstract

An acceptor-donor co-doped (Ga1/2Nb1/2)0.1Ti0.9O2 ceramic is triple-doped with Al3+, followed by sintering at 1450 °C for 5 h to obtain (AlxGa1/2-xNb1/2)0.1Ti0.9O2 ceramics with improved giant dielectric properties. Homogeneous dispersion of all dopants inside the grains, along with the partially segregated dispersion of the Ga3+ dopant along the grain boundaries, is observed. The (AlxGa1/2-xNb1/2)0.1Ti0.9O2 ceramics exhibit high dielectric permittivities (ε′∼4.2–5.1 × 104) and low loss tangents (tanδ∼0.007–0.010), as well as a low-temperature coefficients (<±15%) between − 60 and 200 °C. At 1 kHz, tanδ is significantly reduced by ∼4.4 times, while ε′ is increased by ∼3.5 times, which is attributed to the higher Al3+/Ga3+ ratio. The value of tanδ at 200 °C is as low as 0.04. The significantly improved dielectric properties are explained based on internal and surface barrier-layer capacitor effects, which are primarily produced by the Ga3+ and Al3+ dopants, respectively, whereas the semiconducting grains are attributed to Nb5+ doping ions.