The common phenomenon of the formation of the additional component Psi of the spontaneous polarization resulting from the ordered localization of impurity ions (charged point defccts) in the field of the host polar lattice for polar dielectrics (linear pyroelectrics and ferroelectrics) is established. The additional component is not. in the general case, collinear to the matrix lattice, the spontaneous polarization Psm, and correlates with it as |PSi|. |Psm|-1 < 10-4 In spite of the small value of |PSi|, its temperature dependence at T ≤=s 7 K is the main contribution to the value of the pyroelectric coefficient. Based on the results of investigations of single crystals TGS, LiTaO3 and LiNbO3 with different contents of point defects, the following mechanisms are responsible for changes of the spontaneous polarization, as the temperature decreases from the paraelectric phase: for pure crystals, the mechanism of phase transition (order-disorder or displacive type) ≤ some optical modes anharmonism; for impurity crystals, the mechanism of phase transition (order-disorder or displacive type) ≤ some optical modes anharmonism ≤ impurity ions ordering in the field of host lattice spontaneous polarization. © 1991, Taylor & Francis Group, LLC. All rights reserved.
