Synthesis,Structure And Properties Of Metal Tellurites Nolinear Optical Crystal Materials

The element Tellurium located in A? family of the preriodic table,usually shows two kinds of valences: Te4+ and Te6+,and can form TeO₃,TeO₄,TeO₅,TeO₆ groups,which is flexible and diverse in structure.Because of the lone pair electrons of Te4+ and d10 cation?Te6+?,TeOn units are located in asymmetric coordination environment,easy to have polarity.Its self-combination or connection with other asymmetric units can generate noncentrosymmetric compounds,which have potential application in the ferroelectric,piezoelectric,semiconductor and nonlinear optical materials.Combination of TeOn group and different groups/cations such as Pb2+ cation and [NO₃]-unit with ?-conjugated system result in a series of new tellurite NLO material through hydrothermal reaction.?1?Pb₉Te₂O₁₃?OH??NO₃?₃ is the first example of lead tellurate-nitrate hydroxide NLO crystal.The compound crystallizes in the noncentrosymmetric polar tetragonal space group P43212 with a=12.7268?4??,c=14.5103?5??,?=?=?=90.00°,Z=4.Pb₉Te₂O₁₃?OH??NO₃?₃ features 3D anionic diamond-like toplogical structural motif formulated as Pb₉O₁₃8-constructed by unique nonanuclear basket-shaped Pb@Pb₈O₁₄ clusters,in which Pb@Pb₈O₁₄ clusters shows core-shell structure with one PbO10 polyhedron enclosed by eight PbOx?x=3,4?polyhdera via edge-and face-sharing.The hexavalent Te in TeO₅?OH?octahedra are linked into Pb₉O₁₃8-framework to form novel cationic [Pb₉Te₂O₁₃?OH?]₃+? framework.The compound demonstrates a non-phase-matchable powder second-harmonic generation?SHG?of response about 1.2 times that of KH₂PO₄?KDP?as well as a wide transparency ranges.Calculations on the local dipole moment reveal that the net polarization in the unit cell is zero because of the inverse arrangement of NLO-active units?TeO₆,NO₃ and PbOn?,and the SHG response may result from induced-structure variations by thermal vibrations of the lattice rather than the intrinsic dipole moment.?2?We have obtained four metal tellurites: RbNa₃Te₈O₁₈·7H₂O,RbK₃Te₈O₁₈·6H₂O,Rb₂Te₄O₉·2.5H₂ O and NaPb₄Te₄O₍12 F through hydrothermal reaction.Apart from RbK₃Te₈O₁₈·6H₂O in NCS space group,the other compounds are located in centrosymmetric?CS?space group.The compounds show 2D layer structure,and alkali metal cations and Fanion are filled to maintain charge balance.RbNa₃Te₈O₁₈·7H₂O and RbK₃Te₈O₁₈·6H₂O exhibit a [Te₄O₉]₂-? anion sheet structure by corner-sharing linkage of three TeO₄ seesaws and one TeO₃ trigonal pyramid;the layers generate [Te₆O₁₈]12-6-membered rings?6-MRs?with a star motif and [Te₆O₁₆]8-6-MRs.Rb₂Te₄O₉·2.5H₂ O features a novel wavy [Te₄O₉]₂-? layer consisting of TeO₄ and TeO₅ asymmetric units by sharing edges and corners.NaPb₄Te₄O₁₂F features anunusual [PbTeO₃]? neutral layer made up of PbO₃ and TeO₃ trigonal pyramids,and along the c-axis direction,the sheet produces [Pb₄Te₄O₁₆]8-8-MRs by alternate corner-sharing linkages of PbO₃ and TeO₃ trigonal pyramids.The UV-vis diffuse reflectance spectrum of the four componds show band gaps in the range of 3.12-4.07 eV,indicating that they are wide band gap semiconductors.We calculate the band gap,density of states and dipole moment of RbK₃Te₈O₁₈·6H₂O.In RbK₃Te₈O₁₈·6H₂O,the TeOn group is arranged in reverse order,resulting in polar offsetting and a SHG respond of approximately 1 times ?-SiO₂.Furthermore,the effect of the alkali metal and the distance between the anion layers on the polarity of the compounds were studied.