Hydrothermal Synthesis,Structure And Properties Of Metal Tellurite Optical Crystal

Metal tellurites have received enormous attention because of a wide variety of applications such as birefringence,catalysis,ionic conductivity,and nonlinear-optical(NLO)materials.But it remains a scientific challenge to rationally design metal tellurites owing to diversity of structural units and their possible combinations.In this paper,we introduce alkali metal cations,alkaline-earth metal cations,transition metal cations with d⁰ electron configuration,stereochemically active lone pair cations and halogen ions into the tellurite system through hydrothermal synthesis method.Five metal tellurites have been successfully obtained.The structure and performance of them are discussed and analyzed as follows:(1)Isostructural mixed alkali/alkaline-earth metal tellurite halides BaLiTe₂O₅X(X=Cl,Br)have been successfully synthesized,which crystallize in a monoclinic space group of P2₁/n(No.14).The[Te₂O₅]_?chains by corner-sharing connection of TeO₃ and TeO₄polyhedra are discovered in the two compounds.The[Te₂O₅]_?chains are connected via Li O₃polyhedra to form the[Li Te₂O₅]_?layers.The adjacent[Li Te₂O₅]_?layers are bridged via Ba O₉polyhedra to form the[BaLiTe₂O₅]_?double layers,which is further linked via weak Ba–X–Li interaction to produce 3D framework.Analysis of different lithium tellurites shows that different arrangements of Te-O and Li-O units in the lithium tellurites can be attributed to the cation-cation repulsion and lone-pair effect.BaLiTe₂O₅X(X=Cl,Br)display good thermal stability,wide optical bandgap(4.25 and 4.13 eV)and large birefringence,Showing that they are potential optical birefringent crystal materials.First-principle calculations indicate that the TeO_n groups and X^-determine the optical properties of BaLiTe₂O₅X(X=Cl,Br).(2)Three new tellurite compounds containing second-order Jahn-Teller cations BaPbTe₂O₆,VTe₂O₆(OH)and Pb VO₂(TeO₃)F were successfully designed and synthesized.BaPbTe₂O₆ crystallizes in a polar orthorhombic space group of P2₁2₁2₁(No.24).Pb O₄polyhedra and Te(2)O₃ triangles via corner-sharing create the[PbTeO₅]_?chains.The[PbTeO₅]_?chains are bridged by Te(1)O₃ units,producing 6-MRs[PbTe₂O₆]_?chains which are separated by Ba²⁺cations.BaPbTe₂O₆ has a powder second harmonic generation(SHG)response about two times that of KDP and displays a typical type-I phase matchability.The dipole moment calculation shows that the SHG response arises from the TeO₃ triangles and the Ba O₉ polyhedra.First-principle calculations indicate that the TeO₃ triangles and Ba O₉polyhedra determine the optical properties of BaPbTe₂O₆.VTe₂O₆(OH)crystallize in a orthorhombic space group of Pbca(No.61).TeO₄ polyhedra are linked together into a[TeO₃]_?chain via corner-sharing,and two VO₅(OH)octahedra are interconnected via sharing edge to form the[V₂O₁₀H₂]dimer.[TeO₃]_?chain and[V₂O₁₀H₂]dimer are further linked together into a 3D structure.Pb VO₂(TeO₃)F crystallizes in a orthorhombic space group of Pbca(No.61).Two VO₅F octahedra form a[V₂O₁₀F₂]dimer via edge-sharing,and the two TeO₃ groups are attached to both sides of the dimer in a bidentate bridging mode,giving rise to the[V₂O₄(TeO₃)₂F₂],which are further bridged by Pb²⁺cations.In addition,other reported vanadium tellurites are summarized and analysed systematically.Pb VO₂(TeO₃)F can provide a feasible strategy for the synthesis of vanadium tellurites and enriches the structure of vanadium tellurites.