Study On The Synthesis And Performance Of New Alkali Metals/Alkali Earth Metals Sulfides Crystals

Alkali metals/alkaline earth metal chalcogenides have diverse structures and interesting properties, especially thermoelectricity, solar energy converters, magnetic property,semiconductors, detectors and luminescent property and so on. They have received much attention. However, the common normal infrared materials have narrow transparency range and lower laser-damage threshold. The alkali metals/alkali earth metals sulfides can overcome these defects. This paper focused on alkali metals and alkaline earth metal chalcogenides system. Adopting the high temperature solid state method, a series of new compounds alkali metals and alkaline earth metal chalcogenides compounds were synthesized, and then their optical properties were measured. We proposed a method to prepare the high pure sample,and to overcome the flaw of technology that the quartz tube is easy blasting in the technology process. According to the lattice parameter, we built the structure model, and calculated the properties by the Castep software based on the first principles. The results are in agreement with the practice work, which extended the experimental study. The practice work are shown as follow.Ⅰ. Classical Ternary Alkaline Earth Metal Sulfides:Ba2In2S5 and Ba2In2Se5Through the high temperature solid state method, we get Ba2In2S5 and Ba2In2Se5 compounds, which are different in structure. The layer target compound Ba2In2Q5(Q = S,Se)is connected of In Q4(Q = S, Se) tetrahedral groups by sharing S atoms, and Ba atoms are filled in the space of these layers to balance the crystal structure. But the chain structure of K2Sn2S5 is made by SnS5 groups, and each chain is connected to each other by corner-sharing S atoms. These chains are held together with K cations, giving rise to a 3D framework. The IR spectra show that there is a good transparent in the middle- far-infrared wavelengths(3-20μm). The diffuse reflection spectra show that the band gap are 2.47 eV(Ba2In2S5) and 2.12eV(Ba2In2Se5). First principles calculation results show that the theoretical value is consist with experimental value.Ⅱ. A Series of Quaternary Barium-Antimony Sulfides:BaNa SbQ3(Q = S, Se) and Ba2MSbS5(M = Al, Ga)Through the high temperature solid state method, we get BaNaSbQ3(Q = S, Se) and Ba2MSbS5(M = Al, Ga) compounds. BaNaSbQ3(Q = S, Se) compounds are isostructural, the second kind of Ba2MSbS5(M = Al, Ga) compounds also are isostructural. BaNaSbQ3(Q = S,Se) compounds include alkali metal and alkaline earth metal sulfide elements. As far as we know, it is the first time that the quarternary thioantimonates sulfide were synthesized. The structure of the compounds are described in detail. The first kind of compound, five coordination NaQ5(Q = S, Se) polyhedron and triangle SbQ3(Q = S, Se) groups connect by sharing Q(Q = S, Se) atoms to form the tunnel NaSbQ6(Q = S, Se) anion groups, Ba atoms fill in the tunnel and form the 3Dframesork. The second kind of compound, the isolated SbMS5(M = Al,Ga) unit is formed with pyramid SbS3 units and tetrahedral AlS4 units by sharing S atoms, and the adjacent two anion units direction is opposite, Ba element parallel arranged between the layers. The IR spectra show that it has good transparent properties in the middle-far-infrared wavelength(3-20 μm), the experiment cut-off edge are 395 nm(BaNaSbS3), 500 nm(BaNaSbSe3), 288 nm(Ba2AlSbS5), 400 nm(Ba2GaSbS5). The results of the first principles calcuiations show that the theoretical value is consistent with experimental value.Ⅲ.Classical Ternary Alkaline Metal Sulfides:Na4SnSe4(centre) and Na4SnSe4(noncentre)Through the high temperature solid state method, we get the compound Na4SnSe4(centre)and compound Na4SnSe4(noncentre). The first compound is mainly composed of isolated tetrahedron SnSe4 anionic group and different coordination environment of NaSex polyhedron(x = 4, 5, 6), and the synthesis temperature is 900 oC. The second compound is made by the isolated tetrahedron SnSe4 anionic group and only a kind of coordination environment NaSe5 polyhedron, and the synthesis temperature is 600 oC.