Low-temperature pyroelectric phenomena in lithium niobate single crystals

The results of studying low temperature pyroelectric phenomena in lithium niobate LiNbO 3 single crystals are presented. The temperature dependences of pyroelectric response U-pi (T), dielectric permittivity epsilon(T), changes of electrical charge q(e)(T), thermograms of thermostimulated light emission I-L(T) and non-stationary currents J(N)(T) during heating-cooling runs were investigated in the range of 4, 2 less than or equal to T less than or equal to 300 K. In the vicinity of T* approximate to 200 K we observed the smooth U-pi (T) break, step-like peculiarities of epsilon(T) and the changes of I-L(T) and J(N) (T) thermograms parameters. Near T s approximate to 25 K between the low-temperature maximum of U-pi (T) at 60 K and double 180degrees-change of U-pi phase at 11 K and 6 K is observed the U-pi (T) break, I-L (T) maximum, anomaly of J(N) (T) and change of sign of q(e)(T). The double change of the sign of pyroelectric coefficient is explained in the frame of the microscopic model with account of the defect-subsystem.