Thermal reduction effect on Curie temperature of LiNbO3 ferroelectrics

Dielectric properties of LiNbO3 crystals have been investigated at 1 kHz and 1 MHz frequencies in the temperature range 30–1200 ∘C both before and after annealing in the vacuum. The ferroelectric transition temperature was 1170 ∘C for nonannealed samples, and notably decreases after the reduction. Depending on the annealing time, the maximum of dielectric constant value for reduced crystals was observed at various temperatures down to 670 ∘C; the reduction of the Curie temperature was accompanied by the transition broadening. Two possible mechanisms of transition temperature decrease, due to the formation of deep energy states and to the origination of the lattice strain are considered.