Adamiv V. Іsovalent substituted lithium and barium borates: synthesis, structural features and physical properties.

The thesis is devoted to investigation of influence of isovalent and isotope substitution on physical and technological properties of anhydrous borates - lithium tetraborate (Li2B4O7) and barium metaborate (ВаВ2О4), which are defined as basic ones. It was ascertained that in systems Li2B4O7-А2B4O7 and BaB2O4-МB2O4 the domains of solid solutions are absent, but in the first system the triple compounds exist. There have been developed techniques for synthesis and growth of optically qualitative Li2(1-х)А2хB4O7 and Ba1-хМхB2O4 single crystals, where A = K, Cu, Ag, Cs, Au, and M = Mg, Ca, Zn, Sr, Cd; three-component LiKB4O7 and LiCsB6O10 compounds; isotopically enriched 7Li211В4О7, 6Li210В4О7, 7Li210В4О7, 6Li211В4О7 crystals. There have been shown significant variations in parameters of isovalent and isotopically substituted crystals of basic borates, in particular: in LiKB4O7 there exists the phase-matching direction for SHG; in Ba0.997Sr0.003B2O4 the radiation-damage threshold is twice as high, and values of acoustooptic coefficients are large; Li2(1-x)Cu2xB4O7, enriched by isotopes 6L i 10В, are more sensitive to thermal neutrons. These crystals have been proposed for practical application as detectors and dosimeters of thermal neutrons, acoustic-light modulator for high-power laser radiation. There was demonstrated the dependence of mechanism of neutron-induced radiation defects formation on isotope composition of borates. Experimentally in lithium tetraborate there was ascertained presence of the growth defects - oxygen and lithium vacancies, which play the role of electron and hole traps, and there was refined a nature of vibrational spectra. Using neutron diffraction analysis there was finally proved an absence of structural phase transitions in lithium borates.