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Title:Flux growth, characterization, and structure-property relations for inorganic oxide crystals: Lithium triborate, potassium titanyl phosphate and lead titanate
Author(s):Huang, Yutung
Doctoral Committee Chair(s):Payne, David A.
Department / Program:Materials Science and Engineering
Discipline:Materials Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Materials Science
Abstract:This thesis is concerned with the crystal growth of three different types of inorganic nonlinear dielectric materials, namely, lithium triborate (LBO), lead titanate (PT), and potassium titanyl phosphate (KTP). The electrical and optical properties were determined and related to their structural features and crystal perfection. Manipulation of structure and property improvement was also investigated.
Sizable LBO crystals were grown in this research. However, cracking during cooling was a major limiting factor in obtaining large single crystals. By using a post-growth cooling program, the problem was partly solved. For the growth of PT crystals, a double-crucible technique was developed and used with accelerated crucible rotation. The self-flux method reduced the evaporative loss of lead oxide and improved crystal quality. Isometric crystals were obtained of high quality and size. A floating-seed technique was developed for KTP crystals. The growth procedure, included: soaking, quenching, seeding, thermal cycling and slow cooling in a regular box furnace. Large KTP crystals of high quality were obtained. Based on the experimental observations, a complex flow pattern and an anisotropic surface diffusion mechanism were proposed for the floating seed method.
Electrical measurements identified relaxation of polarization along the polar axis for all three types of materials. Kramers-Kronig transformations were used to subtract additional contributions from the relaxation polarization. Diagnosis of the normalized loss spectra, indicated, long-range hopping and short-range interactions, as the probable origin of the relaxation behavior. These results are discussed in terms of structural features and crystal perfection which were characterized by chemical analysis, density measurements and electron paramagnetic resonance studies.
Optical transmission spectra for the crystals in the UV/VIS regime indicated that the bandgap energy was mainly determined by their respective anionic clusters (i.e., the BO$\sb6$ group in ABO$\sb3),$ following LBO $>$ KTP $>$ PT. IR transparency had the reverse sequence: PT $>$ KTP $>$ LBO. The cut-off wavelengths were attributed to the first overtones for the fundamental vibrations in TiO$\sb6,$ PO$\sb4,$ and BO$\sb3$ clusters, respectively.
Structural modifications to KTP crystals were designed by Ti-site (B-site) doping with different transition metals which were incorporated during crystal growth. Post-growth exchange reactions for the potassium-site (A-site) cation with benzoic acid were also investigated. Dielectric relaxation in KTP crystals was effectively suppressed by incorporation of Cr$\sp{3+}$ ions, which was attributed to a charge compensation mechanism. Both the higher frequency dielectric polarization, and the optical nonlinearity, were enhanced. In addition, optical absorption and photoluminescence for Cr$\sp{3+}$ were used to determine a crystal field of Dq/B $\approx$ 2.06. The results indicate a significant degree of covalency for the highly distorted octahedral anionic group in the KTP structure.
Issue Date:1993
Rights Information:Copyright 1993 Huang, Yutung
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9411656
OCLC Identifier:(UMI)AAI9411656

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