Nonlinear optical oxide crystals

Defect Chemistry of Nonlinear Optical Oxide Crystals... 

The defect chemistry of nonlinear optical oxide crystals can affect many of the materials properties required for device applications. Applications of these crystals,... 

The purpose of this paper is to summarize the current understanding of the defect chemistry of nonlinear optical oxide crystals and specifically the relationship of the defects present to 1) the structure and growth, or processing, of the material and 2) the properties of interest for device applications. The defects in traditional nonlinear optical oxide crystals (i.e. BaTiC>3, LiNbC>3, Sri-xBaxNb206, Ba2NaNb50l5, K3Li2Nb50l5) are reviewed. Our recent work on the defect chemistry of new... 

Several isovalent ions form solid solutions with KTP (Table II), showing that this structure is relatively tolerant, with respect to isovalent impurities, as are the traditional nonlinear optical oxide crystal structures. But due to the relatively limited range of nonstoichiometry in KTP, aliovalent impurities, such as divalent Ba, Sr and Ca introduced through ion exchange in nitrate melts, which substitute on the K site, are incorporated at concentrations less than one mole percent.(36) Typical impurity concentrations present in flux and hydrothermally grown KTP are shown in Table ID. 

The nonlinear optical oxide crystals recently developed are grown by flux (and hydrothermal solution for KTP) techniques to prevent decomposition (KTP, KTA, LBO) or to obtain a low temperature phase (BBO). The intrinsic nonstoichiometry and the impurity contents of the as-grown crystals is determined by the solutions and temperatures used for growth. The intrinsic defect concentrations in these materials are relatively low, compared to the more traditional nonlinear optical oxides having the... 

The basic structural units responsible for the second order nonlinear optical susceptibility in most oxide crystals are the acentric anionic groups. (4,6) The... 

These mixed oxides have been considered as nonlinear optical materials (see Nonlinear Optical Materials). They crystallize as ordered derivatives of the cristobalite structure. As early X-ray structural studies were performed on twinned crystals grown from congment melts, their true symmetry was not firmly established. Untwinned single crystals have been produced by hydrothermal methods, and the space group has been convincingly established as 14. 

Solid phosphates show a huge variety of crystal structures, and it is not practical to classify them in terms of structural types as is done with simple oxides, halides, etc. However, some general classes of metal phosphate structures will be considered three-dimensional frameworks of linked phosphate tetrahedra and tetrahedrally or octahedrally coordinated cations, layered phosphates, and phosphate glasses. In all of these materials the size and topology of pores within the structure are of importance, as these determine the ability of ions and molecules to move within the structure, giving rise to useful ion exchange, ionic condnction, or catalytic properties. Ion exchange can also be nsed to modify the properties of the host network, for example, the nonlinear optical behavior of potassium titanyl phosphate (KTP) derivatives. 

Ferroelectric crystals (especially oxides in the form of ceramics) are important basic materials for technological applications in capacitors and in piezoelectric, pyroelectric, and optical devices. In many cases their nonlinear characteristics turn out to be very useful, for example in optical second-harmonic generators and other nonlinear optical devices. In recent decades, ceramic thin-film ferroelectrics have been utilized intensively as parts of memory devices. Liquid crystal and polymer ferroelectrics are utilized in the broad field of fast displays in electronic equipment. 

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