Calculation of local electric fields in displacive-type ferroelectrics: LiNbO3

The method is suggested for calculating the intensity and potential of a lo cal electric field in displacive-type ferroelectrics which is based on the introduction of a transitional zone between the region of the discrete loca lization of ions and the homogeneously polarized medium. The method is exem plified on the calculation of the contribution of Li+ ions to the local ele ctric field in the lithium niobate structure. It is shown that the method p rovides fast convergence of the results in the calculation of the field int ensity and high relative accuracy of the calculated electric-field potentia l inside the crystal. The contribution of the induced dipoles to the local electric field is calculated, and it is shown that the stability of the LiN bO3 structure is provided by considerable anisotropy in the polarizability of Nb-O bonds. The method is applicable to any ionic crystal. (C) 2000 MAIK "Nauka/Interperiodica".