| Crystal is an important medium for the conversion of various energy,including light,heat,electricity,force,sound,and magnetism.As the core material of high technology development,crystals have important and extensive applications in the fields of microelectronics,communications,medical treatment,aerospace,and modern military technology.The rapid development of science and technology promotes the continuous innovation of crystals.Due to the inherent properties of tellurium containing lone-pairs electrons and valence diversity,tellurate crystals have become an important part of photoelectric functional crystals,and have potential applications in the fields of birefringence,catalysis,magnetism,piezoelectricity,ferroelectric,nonlinear,semiconductor,and so on.For the urgent demands of mid-infrared nonlinear optical(NLO)crystals in the military and civilian fields,Li2MTeO6(M=Ti,Sn)is selected as the research object to play the energy band regulation characteristics of hexavalent tellurate with taking into account the laser damage threshold and NLO coefficients.For the urgent demands for detection materials,MTe3O8(M=Ti,Zr,Sn)with Te4+ cations containing lone-pair electrons is selected as the research object based on the X-ray detection mechanism,and oxygen crystals exhibit high crystal quality and high-temperature environmental stability.Based on the above guidance,the potential applications of tellurate crystals are explored in the fields of mid-infrared NLO material and Xray detection material.(1)Li2TiTeO6 crystal is selected as a potential oxide mid-infrared NLO crystal for the first time.The chalcogenides and pnictides mid-infrared NLO crystals exhibit large NLO coefficients and broad transparent regions.However,there are shortcomings such as severe optical absorption,low laser damage threshold,and harsh crystal growth conditions,which limits their practical applications.Therefore,the heavy metal element of tellurium is preferred to widen the infrared cutoff edge of the material.Meanwhile,oxide crystals can be grown by the melt method,which can easily obtain high-quality crystals.Li2TiTeO6 is selected as a potential oxide mid-infrared NLO crystal based on the high damage threshold and large NLO coefficient.High-quality and large-sized Li2TiTeO6 and Li2SnTeO6 single crystals were successfully grown by flux method,and the maximum size of Li2TiTeO6 single crystal can reach 35×12×20 mm3.Both high-resolution X-ray and Laue diffraction indicate that the high quality of as-grown crystals.Both Li2TiTeO6 and Li2SnTeO6 belong to the orthorhombic crystal system,Pnn2 space group,and they are non-centrosymmetric structures.The structures of Li2TiTeO6 and Li2SnTeO6 are similar.TiO6 octahedrons(SnO6 octahedrons)and TeO6 octahedrons are connected through corner-sharing and edge-sharing,forming hexagonal tunnels along the caxis direction,and two types of Li+ cations are located in the hexagonal tunnels.Finally,a stable three-dimensional network structure is formed.The optical properties of Li2TiTeO6 and Li2SnTeO6 crystals were systematically researched for the first time.Li2TiTeO6 and Li2SnTeO6 crystals exhibit large band gaps(3.74 eV and 4.00 eV),wide transmission ranges(380-6700 nm and 380-6868 nm),high laser damage thresholds(591 MW/cm2 and 672 MW/cm2),and strong second harmonic generation responses(26 times and 2.5 times that of KDP crystal),and both crystals can achieve type I phase matching.The dipole moments of polyhedrons in Li2TiTeO6 and Li2SnTeO6 crystals were calculated by the valence bond theory.The relationship between the second harmonic generation responses and crystal structures was analyzed.The relationship between the optical properties and crystal structures of Li2TiTeO6 and Li2SnTeO6 crystals was further elucidated by first-principles calculations.Based on these excellent properties,Li2TiTeO6 crystal is selected as a potential mid-infrared nonlinear optical crystal.In addition,the thermal properties of Li2TiTeO6 crystal were systematically studied,which exhibits large specific heat,small thermal expansion coefficient,and high thermal conductivity.The relationship between the thermal anisotropy and the crystal structure has been studied.(2)A theory of "enhancement effect of cations containing lone-pair electrons on X-ray detection performance" is proposed by us for the first time.The photoelectric effect and Compton scattering effect are the main mechanisms to explain the X-ray detection performance of materials.By introducing tetravalent tellurium cations containing lone-pair electrons into the compound,we expect that lone-pair electrons can not only jump to the inner holes but also provide outer free electrons to realize the Compton scattering effect in X-ray detection,which expects to form a novel high-performance X-ray detection material.Based on the above analysis,MTe3O8(M=Ti,Zr,Sn)is selected as the research object.The Compton scattering effect is proved by theoretical analysis and experiment when materials containing lone-pair electron cations interact with X-rays.Moreover,based on the sensitivities of materials containing lonepair electrons and without lone-pair electrons,the sensitivities of the X-ray detectors containing Te6+cations(without lone-pair electrons)are much lower than that of materials containing Te4+cations with lone-pair electrons.These experimental results show that the cations containing lone-pair electrons have an enhancement effect on the X-ray detection performance,which provides a new idea for optimizing new high-performance X-ray detection materials.(3)SnTe3O8 crystal containing lone-pair electrons cations was selected as a potential hightemperature X-ray detection crystal for the first time.Recently,α-Se,CdZnTe,and some perovskites have been applied in direct X-ray detectors.However,some disadvantages of these materials limit their practical applications in high-temperature X-ray detectors,including low thermal stability,internal defects,and poor detection performance.Because of the vacancy of high-temperature X-ray detection materials,SnTe3O8 is chosen as the research object to aim the enhancement effect of Te4+cations containig lone-pair electrons on the X-ray detection performance and the high-quality crystal and high-temperature environmental stability of oxide crystal.High-quality SnTe3O8 single crystal has been grown by the flux method.SnTe3O8 belongs to the cubic crystal system,Ia-3 space group.Each SnO6 octahedron is connected with six TeO4 polyhedra through corner-sharing to form a[SnTe6O20]structural unit.Meanwhile,two[SnTe6O20]structural units can be connected by another TeO4 polyhedron.The SnO6 octahedrons and TeO4 polyhedrons are interconnected and stacked to form a three-dimensional network structure.SnTe3O8 single crystal exhibits a high density(6.042 g/cm3),a high resistivity(2×1014Ωcm),a low defect state density(9.14×109 cm-3),a high carrier mobility(0.48 cm2V-1 s-1)and a high carrier mobility lifetime product(3.22×10-4 cm2 V-1).Meanwhile,SnTe3O8 single crystal has high thermal stability(850℃),large band gap(2.82 eV),large specific heat(0.849 J g-1 K-1),small thermal expansion coefficient(6.74×10-6 K-1),and high thermal conductivity(3.34 W m-1 K-1),which indicates that SnTe3O8 crystal has potential applications in hightemperature X-ray detection.The ion migration and X-ray detection performance of MTe3O8(M=Ti,Zr,Sn)crystals were systematically characterized for the first time.SnTe3O8 crystal has the largest ion migration activation energy(1107.5 meV)and the highest O2-ion theoretical migration barrier(2.07 eV),which shows the weak ion migration of SnTe3O8.In addition,SnTe3O8 has ultralow dark current drift(2.44×10-9 nA cm-1 s-1 V-1),high room temperature sensitivity(436 μC Gyair1 cm-2),stable high-temperature sensitivity(61 7 μC Gyair-1 cm-2),ultra-low detection limit(8.19 nGyair s-1),fast response time(386 ms),long-term device performance stability,clear room temperature and high-temperature X-ray imaging capabilities.SnTe3O8 crystal has potential applications in high-temperature hard X-ray detection,low-dose radioactive personnel protection,and personal dose monitoring applications.Based on these excellent X-ray detection properties,SnTe3O8 crystal is selected as a potential novel high-temperature X-ray detection crystal.These results not only optimize the potential novel mid-infrared NLO crystal Li2TiTeO6 and high-temperature X-ray detection crystal SnTe3O8.Meanwhile,these experimental results also verify that Te6+ cations can expand the infrared cut-off edges of materials,and Te4+ cations containing lone-pair electrons exhibit enhancement effect for X-ray detection performance,which provide theoretical guidance and reference for the design of novel optoelectronic materials. |
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