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

In this study, La + Nb co-doped TiO2(LNTO;x = 0, 0.02, 0.05, 0.07) ceramics were prepared by the solid-state reaction method with high-purity TiO2, La2O3 and Nb2O5 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 (epsilon ' > 10(4)) and that the dielectric loss is relatively low (tan delta similar to 0.1) compared with that of pure TiO2(epsilon ' similar to 10(2)) at low frequency. Within the test temperature range (30-500 degrees 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 TiO2.