Syntheses,Crystal Structures And Properties Of Chalcogenides Containing Alkaline(Alkaline-earth) Metal

Infrared nonlinear optical(IR-NLO)materials have important applications in the field of optoelectronics,and their exploration is one of the difficulties and frontiers in the field of NLO materials research.At present,the wide applications of commercial AgGaS2,AgGaSe2 and ZnGeP2 are limited due to their low laser damage thresholds(LIDT)or two-photon absorption defects.Therefore,exploration of new IR NLO is a hot area at present.Chalcogenides have large NLO coefficient and wide infrared transmission range,which become an important part of IR-NLO materials research.As we know,the chalcogenides containing distorted polyhedron units often have large NLO effect.In this thesis,the strategy of introducting alkali(or alkali earth)metal into the chalcogenides was adopted to widen the band gap and to improve the laser-induced damage threshold of the compounds,which will be benefit to abtain new NLO materials with large NLO coefficient and large LIDT.Guided by this thought,during the exploration of IR NLO materials in the alkali metal or alkaline earth metal-containing chalcogenides,two quaternary phosphorous sulfides Ca1.3Pb0.7P2S6(1),Rb2FeP2S6(2),two ternary sulfides Cs4Ga6S11(3),BaGa2S4(4),and two quaternary chalcogenides KInSSe(5),BaIn2S2.92Se1.08(6)were synthesized by alkali metal or alkaline earth sulfides or halide flux methond.The synthesis,structure and properties of these compounds are discussed in this thesis.The preliminary research results of the thesis are as follows:1.Through the reactions of alkali(or alkaline-earth)metal,PaSbn-anionic groups and metals(Pb,Fe)with lone electron pairs,two quaternary chalcogenides CaPbP2S6(1)and Rb2FeP2S6(2)were synthesized by high temperature solid state synthesis method,they crystallize in the space groups of P2l/n and P2l/c,respectively.Compound 2 possess one dimensional structure,in which Fe atom was coordinated by six S atoms to form a distorted octahedral FeS6 unit.Two neighboring phosphorus atoms each possess tetrahedral coordination of one P atom and three S atoms,joining into pairs by P-P bond.Each pair is surrounded by six S atoms,forming a distorted P2S6 octahedron.All octahedral FeS6 and P2S6 units are connected by sharing S atoms in the two opposite faces to form infinite one-dimensional 1?[FeP2S62-]chains extending along the a direction,between which the counter cations Rb+ are embedded.Compound 2 is antiferromagnetic,the intrachain antiferromagnetic coupling and interchain ferromagnetic coupling transitions occur at-27 K and-2 K respectively.UV diffuse reflectance spectrum shows that the optical band gap of the compound is 2.03 eV.In addition,theoretical calculation shows that the theoretical band gap value is 1.95 eV.2.By the alkali or alkaline earth sulfide flux method,we have obtained two themary sulfides Cs4Ga6S11(3)and BaGa2S4(4),and two quaternary chalcogenides KInSSe(5)and BaIn2S2.92Se1.08(6).Compounds 3 and 4 crystallize in the space groups of P-1 and Fddd,respectively.Compounds 5 and 6 crystallize in C2/c and Fddd,respectively.Ga or In in these compounds form tetrahedral coordination with four S.They form 1D(4)and 2D(5 and 6)structures by sharing corners or edges.Interestely,In(S/Se)4 tetrahedra are corner-shared with each other to form In4(SxSe1-x)10 supertetrahedron in compound 5.In compound 6,In(S/Se)4 tetrahedra are corner-and edge-shared with each other to form two-dimensional(In2S2.92Se1.08)-layers.IR measurements reveal that compounds 3-6 are optically transparent in the range of 4000-400 cm-1.UV diffuse reflectance measurements showed that the optical band gaps of compounds 3 and 4 were 2.76 eV and 2.66 eV,respectively.In addition,theoretical calculation indicates that the band gaps of 3-6 are 2.982 eV,2.809 eV,2.134 eV and 2.290 eV,respectively.