Ionic Group Theory for Electrophoto and Nonlinear Optical Effects of Crystals. III. Calculations of Electrophoto and Multifrequency Coefficients of LiNbO sub 3 , LiTaO sub 3 , KNbO sub 3 and BNN Crystals Using an Ionic Group Model

摘要

If the O/sub h/ symmetry is assumed, the oxygen octahedrons in these crystals will possess the same energy levels and symmetrical wave functions. By using the group representation theory, the energy levels and the symmetrical wave functions of the oxygen octahedrons in the C sub 3 /sub nu/, C sub 2 /sub nu/ symmetry can be obtained. By further using the ABDP theory, their electrophoto and multifrequency coefficients can be calculated. The calculated results agree with experiments quite well. The paper also explains theoretically the relationships among the magnitudes and signs of the multifrequency coefficients of these crystals and the deformations of the oxygen octahedrons. Two conclusions can be obtained from these: (1) the ionic group model of the deformed oxygen octahedron is suitable for not only calcium-titanium ore-type materials but also tungsten-bronze-type and LiNbO sub 3 materials; (2) in the tungsten-bronze-type and LiNbO sub 3 -type materials, ionic bonds still make major contributions to electrophoto and multifrequency effects. Since the covalent bond fraction of LiTaO sub 3 is greater than that of LiNbO sub 3 , the nonlinear optical effect of LiTaO sub 3 is smaller than that of LiNbO sub 3 . (ERA citation 08:036562)