Synthesis and nonlinear optical properties of BaTi(BO3)2 and Ba3Ti3O6(BO3)2 crystals in glasses with high TiO2 contents

The ternary BaO-TiO2-B2O3 glasses containing a large amount of TiO2 (20-40 mol%) are prepared, and their optical basicities (Lambda), the formation, structural features and second-order optical nonlinearities of BaTi(BO3)(2) and Ba3Ti3O6(BO3)(2) crystals are examined to develop new nonlinear optical materials. It is found that the glasses with high TiO2 contents of 30-40 mol% show large optical basicities of Lambda = 0.81 - 0.87, suggesting the high polarizabity of TiOn polyhedra (n = 4-6) in the glasses. BaTi(BO3)(2) and Ba3Ti3O6(BO3)(2) crystals are found to be formed as main crystalline phases in the glasses. It is found that BaTi(BO3)(2) crystals tend to orient at the surface of crystallized glasses. The new XRD pattern for the Ba3Ti3O6(BO3)(2) phase is proposed through Rietvelt analysis. The second harmonic intensities of crystallized glasses Were found to be 0.8 times as large as alpha-quartz powders, i.e., I-2 omega(sample)/I-2 omega(alpha-quartz) = 0.8, for the sample with BaTi(BO3)(2) crystals and to be I-2 omega(sample)/I-2 omega(alpha - quartz) = 68 for the sample with Ba3Ti3O6(BO3)(2) crystals. The Rarnan scattering spectra for these two crystalline phases are measured for the first time and their structural features are discussed. (c) 2005 Elsevier Inc. All rights reserved.