A LOCALIZED QUANTAL THEORETICAL TREATMENT, BASED ON AN ANIONIC COORDINATION POLYHEDRON MODEL, FOR THE EO AND SHG EFFECTS IN CRYSTALS OF THE MIXED-OXIDE TYPES

In order to establish a reliable theoretical basis for designing and synthesizing now electro-optic and nonlinear optical crystals, we have made a systematic investigation on the dependence of these optical properties in crystals of the mixed types upon their internal structure. As a result, we take that these optical properties originate from the anionic groupings, and thus present here a theory of anionic coordination polyhedra. By using localized orbital calculations, we can easily obtain: first, a quantitative dependence of the electro-optic, (EO) and the optical second harmonic (SHG) effects in perovskitetype and tungsten-bronze-type crystals upon the distortion of these anionic oxygen-octahedra; secondly, a quantitative explanation of the SHG effects of iodates from the (IO3) groupings, the structure of which may be regarded as a highly distorted oxygen-octahedron; and thirdly, a qualitative explanation of the optical SHG effects of other mixed-oxide type crystals (such as phosphates, molybdates, and sodium nitrite) from their respective (PO4), (MoO4), (MoO4), (AsS3) and (No2) groupings.