Giant permittivity up to 100 MHz in La and Nb co-doped rutile TiO2ceramics

Dielectric spectroscopy was carried out for reduced and stoichiometric La(0.0025)Nb(0.0025)Ti(0.995)O(2)ceramics synthesized by sintering in different atmospheres. A giant permittivity (~1 x 10(4)) was obtained at a frequency of 100 MHz and temperature range from 170 to 350 K. Three dielectric relaxation mechanisms were observed within the temperature range of 10-300 K via dielectric spectroscopy. A low temperature dipole relaxation peak (in the temperature range of 10-30 K) in the spectra was identified to be associated with the giant permittivity specifically measured at 100 MHz. The origin of such giant permittivity was attributed to dipole orientation polarization. Hopping polaron and interfacial effect contributed to giant permittivity. After annealing treatment, all the relaxation contributions were weakened. Low dielectric loss was attributed to high resistance of grain and grain boundaries. Annealing in ambient conditions led to decreased relaxation times which gives the signature of decreased concentration of oxygen vacancies and Ti3+. Dipoles which were related to oxygen vacancies and Ti3+, resulted in giant permittivity up to 100 MHz.