Synthesis,Structure And Properties Of Several New Alkaline Earth Metal Titanium Iodate Crystals

Nonlinear optical crystals are the core basic materials for solid-state lasers to achieve wavelength expansion and have very important applications in many high-tech fields such as military,scientific research and medical treatment.For nonlinear optical crystals with excellent performance,they need to meet some structural and performance requirements,including non-centrosymmetric structure,large multiplier effect,wide transmission range and easy crystal growth.The standing chemical activity of the lone pair electrons of I⁵⁺in iodate can usually produce large distortions in the structure and make the structure easier to crystallize in the non-centrosymmetric space group,therefore,iodate is one of the main material systems for nonlinear optical crystal research.In this thesis,five new transition metal iodate crystals were designed and synthesized in the Ba-Ti-I-O system by introducing d⁰ transition metal cations,which are prone to the second-order Jahn-Teller distortion,into iodate to further increase the material distortion.And the laws and mechanisms of their reaction conditions,crystallization water and halogen anions on the structure and properties of transition metal iodates were systematically investigated.1.The first homogeneous polycrystalline?-and?-Ba Ti(IO₃)₆ with the same space group and similar cell parameters but different phases were designed and synthesized by regulating the reaction conditions.this is the first case of d0 transition metal iodate with the same space group and similar cell parameters but different phases.this work will provide some new insights into the phase transition of iodate.2.The evolution of the centrosymmetric Ba Ti(IO₃)₆ to the non-centrosymmetric Ba Ti(IO₃)₆?0.5H₂O structure was achieved based on the modulation of the transition metal iodate structure by crystalline water.How to design and synthesize non-centrosymmetric structures has been an important topic in the research of nonlinear optical crystals.In this study,we successfully synthesized a novel non-centrosymmetric transition metal iodate Ba Ti(IO₃)₆?0.5H₂O by introducing water of crystallization in Ba Ti(IO₃)₆ by hydrothermal method,and this work provides a new idea to obtain non-centrosymmetric compounds through structural modulation.3.The first fluorine-containing titanium iodate salt was synthesized by introducing halogen anions,and its structure was designed by molecular tailoring to degrade its structure and obtain a new titanium iodate salt.The first fluorine-containing titanium iodate Ba Ti I₄O₁₂F₂ was obtained by successfully introducing the element F into the Ba-Ti-I-O system through hydrothermal synthesis,and this work confirmed the feasibility of introducing the element F into this system.Secondly,by the design idea of molecular tailoring,the Ba F₂ molecule was cut off based on Ba Ti I₄O₁₂F₂ to obtain a new one-dimensional chain structure of titanium iodate compound Ti I₄O₁₂.The synthesis of both compounds further enriched the structural chemistry of iodates.