Polaron-mediated low-frequency dielectric anomaly in reduced LiNbO3:Ti

Measurements of the real and imaginary parts of the dielectric permittivity of reduced Ti-doped lithium niohate reveal a low-frequency dielectric relaxation as well as a strong increase in the conductivity compared to undoped samples. The low-frequency permittivity is increased by about an order of magnitude due to the relaxation. The analysis of the temperature-dependence of the relaxation frequency reveals a thermally activated behavior with an activation energy of E-a = 0.65 cV, which is in agreement with a transition between Nb-Li(4+) small bound polarons and Nb-Nb(4+) free polarons. Both low-field ac conductivity and high-field dc conductivity indicate a Poole-Frenkel-type electron hopping mechanism between Nb-Nb(4+) sites at low temperature, turning into similar hopping between Nb-Nb(4+) at high temperatures. tures. (C) 2017 Author(s).