Rare Erath Sulfide Borate

It is an attractive subject to design crystal materials with new structure.In the development of science,crystal with more novel structure can play two roles:one is to assist in the research and development of basic theory,the other is to obtain crystal materials with better or novel performance to meet people's production and life needs.As a long-range ordered material,one of the possible ways to obtain crystals with new structures or excellent properties is to combine two or more functional units with different effects in one structure.Structurally speaking,the structure thus obtained is more likely to be brand-new.From the aspect of structure-activity relationship,different functional units can be combined into a structure,or coordinate the orderly arrangement of functional units,so as to obtain crystal materials with excellent performance and/or various functions.In this thesis,rare earth ions,sulfur ions,and borate ions are introduced into a structure for the first time to form a new structure and compound system of rare earth sulfide borate.For the application of materials in optical field,sulfur ions have a large ionic polarization,while borates often have a large band gap.From the magnetic properties point of view,rare earth elements are very good magnetic ions,and China's rare earth resources are very rich.Therefore,the purpose of this study is to combine rare earth ions,sulfur ions and borate ions into one structure,synthesize crystals with such novel structures,and study their optical and magnetic properties.The main contents are as follows.1.The first rare earth sulfide borate structure.The crystal structure,optical and magnetic properties of RE3S3BO3(RE=Sm,Gd)are introduced.The anions in the structure are(BO3)3-and S2-,and there is no bonding between them,so it is totally different from any previous structure including thioborate and sulfate.The discovery of this structure represents the birth of a new type of structural system,namely,rare earth sulfide borate.The experimental optical band gaps of Sm3S3BO3(SSBO)and Gd3S3BO3(GSBO)are 2.50 eV and 2.65 eV,respectively.The electronic structure of GSBO is calculated by the highly accurate all-electron full-potential linearized augmented plane-wave(FP-LAPW)method.The results show that GSBO is an indirect band gap semiconductor.SSBO shows a typical Van Vleck-type paramagnetism.The intensity of exchange interaction is estimated based on the low temperature susceptibility of 2-20 K.The effective g-value geff and Curie-Weiss temperature are 0.443 and-2.87 K,respectively.However,GSBO exhibits antiferromagnetic behavior at low temperature,with a Neel temperature of?5.9 K and an asymptotic Curie temperature of-6.04 KIn order to obtain novel magnetism,the dimensionality of the arrangement of magnetic ions is regulated.2.Bilayer-Kagome slabs structure.The sulfide borate Eu6MgNb2S(B4O10)2O6(EMNSBO)is studied,because it contains three kinds of anions:S2-,(B4O10)8-and O2-,which can be more precisely named oxysulfide borate.The electronic structure and birefringence are calculated by the highly accurate all-electron FP-LAPW method.Although the ground state of Eu3+ is non-magnetic ion,there is a unique bilayer-Kagome slabs in this structure,and the distance between the bilayer-Kagome slabs is up to 5.22 A.The(B4O10)8-in the structure is also a new boric acid radical.The atomic charges are determined by topological analysis of the experimental dynamic charge density,and the experimental deformation dynamic charge density of(B4010)8-is analyzed.All of these provide a good reference for the follow-up research.The optical band gap of EMSBO is determined as?2.92 eV by UV-vis-NIR spectrum and the temperature dependent magnetic susceptibility measurement shows that the EMNSBO exhibits Van Vleck-type paramagnetism.3.Triple-Kagome-layer slabs structure.The sulfide borate Eu9MgS2B20O41(EMSBO)is studied,and its structural and physical properties are characterized.EMSBO consists of triple-Kagome-layer slabs separated by nonmagnetic ions and groups.Within each slab,intervalence charge transfer(IVCT)be found to occur between the Eu2+ and Eu3+ Kagome layers,a new channel for quantum fluctuation of magnetic moments.The measured magnetic susceptibilities and the specific heat capacity exhibit very similar features characteristic of quantum spin liquid(QSL)behaviors observed in other materials.In order to obtain rare earth sulfide borate being second-order nonlinear optical(SO-NLO)activity,the structural symmetry is controlled.4.Noncentrosymmetric rare earth sulfide borate.The crystal structure,optical and magnetic properties of Eu2B5O9S(EBOS)are studied.Although the structure is noncentrosymmetric,no obvious second harmonic generation(SHG)signal is detected.Combined with the UV-vis-NIR absorption spectrum and the first-principle calculation,it is speculated that the strong absorption of charge transfer state(CTS)and the small SHG coefficients of the sample are the reasons why the crystal has no obvious SHG response.Magnetic measurement shows that EBOS is a ferromagnetic material with Curie temperature of?16.0 K.5.Noncentrosymmetric rare earth sulfide borate with SO-NLO behavior.On the basis of the previous chapter,the sulfides borate EU4.5(B5O9)2SI(EBOSI)are obtained by adjusting the synthesized strategy.It can be more precisely named as thio-halide borate,which is also the first chalcohalide borate found.EBOSI shows good SO-NLO behavior,i.e.the SHG response of powder with medium strength is about 0.5 times of that of AgGaS2,and the high laser induced damage threshold(LIDT)is about 15 times of that of AgGaS2,and phase matching can be achieved.Furthermore,the structural design strategy and experimental results are verified by theoretical calculation,and it is found that Eu2+cations in the structure contribute a lot to the SO-NLO optical efficiency of the material.Magnetic measurement shows that there is antiferromagnetic interaction in EBSOI,but there is no antiferromagnetic order until 2 K.