Preparation and properties of La and Nb co-doped TiO2 colossal dielectric ceramic materials

In this study, La + Nb co-doped TiO 2 (LNTO; x = 0, 0.02, 0.05, 0.07) ceramics were prepared by the solid-state reaction method with high-purity TiO 2 , La 2 O 3 and Nb 2 O 5 powders. LNTO ceramics show dense microstructures with the second phase at the grain boundary, and La and Nb addition can inhibit the grain growth. Results of dielectric properties show that the dielectric constant of LNTO ceramics are enhanced largely ( ε ′ > 10 4 ) and that the dielectric loss is relatively low (tan δ ~ 0.1) compared with that of pure TiO 2 ( ε ′ ~ 10 2 ) at low frequency. Within the test temperature range (30–500 °C) and test frequency range (0.5–1000 kHz), dielectric constants of LNTO ceramics display relatively high stability. The two peaks in modulus spectra could be explained by Maxwell–Wagner polarization. The results of dielectric and impedance spectra prove that the internal barrier layer capacitance model can be used to explain the colossal permittivity in (La + Nb) co-doped TiO 2 .