Study On Structural Phase Transition And Photoelectric Response Characteristics Of SnS₂ And ReS₂ Under High Pressure

Transition metal disulfide（TMDs）have a wide band gap range,strong conductivity,high flexibility,and have excellent application prospects in the fields of electronics,photoelectronic,photocatalysis and other fields,and has been widely concerned by researchers.High pressure is an extreme condition that can regulate materials in terms of structure or properties.Changes in the structure and properties of substances under such extreme conditions can deepen our understanding of the material world and contribute to further exploration of new structures and properties of materials.Under the action of external pressure,the interlayer force of TMDs changes dramatically.In addition,the crystal structure and electronic structure of TMDS will also change significantly,such as semiconductor-metal transition and superconducting transition.In this paper,two kinds of semiconductor TMDs,SnS₂crystal with 2H structure and ReS₂crystal with distorted 1T structure,were selected as the research objects to study the influence of pressure on the structure and photoelectrical properties of 2H-SnS₂and distorted 1T-ReS₂.The main findings of this paper are as follows:1.The evolution of the structure and photoelectric properties of 2H-SnS₂under high pressure was systematically studied by high pressure in situ X-ray diffraction（XRD）,Raman,UV-visible light absorption and high pressure photoelectric measurement.The results show that the 2H-SnS₂crystal does not undergo structural phase transition under pressure up to 24 GPa,and the bulk modulus is 57.8 GPa.The decrease of layer spacing significantly affects the optical absorption properties of2H-SnS₂crystals.Under pressure,the hybridization of p_zorbital of S atom is enhanced,and its band gap decreases with the increase of pressure,showing a tendency to decrease to closure.Correspondingly,the 2H-SnS₂absorption edge redshifts with the increase of pressure,resulting in the absorption of more wavelength range of light.The study of photoelectric characteristics shows that the photoelectric signal of 2H-SnS₂under pressure goes through the process of first strengthening,then weakening and then strengthening.When the pressure reaches 32.4 GPa,the photoelectric signal intensity reaches the highest value,which is 37 times of the initial pressure value.The resistance measurement shows that the density of the sample increases and the crystal defects decrease with the increase of pressure from 0 GPa to3 GPa,resulting in the decrease of the resistance.Over 3 GPa,the lattice begins to distort and deform,and the sample crystallinity deteriorates,leading to an increase in resistance with pressure.Above 15 GPa,the 2H-SnS₂band gap further decreases with the increase of pressure,which leads to the decrease of resistance.The variation of2H-SnS₂photoelectric signal is consistent with the variation trend of its resistance under high voltage.These results indicate that pressure can not only change the crystal structure of the material,but also control its photoelectric response.2.The structure,optical properties and photoelectric properties of distorted1T-ReS₂under high pressure were studied by in-situ XRD,Raman,UV-visible absorption and photoelectric testing.The results show that the structure of ReS₂crystal changes from the distorted 1T structure to the distorted 1T’structure at 7.5 GPa,which is maintained until the maximum experimental pressure of 27.9 GPa.Under pressure,the lattice parameters of ReS₂gradually decrease,the interatomic interaction is enhanced,and the band gap becomes smaller.The high-voltage photoelectric test results show that the photocurrent of ReS₂increases gradually with the pressure under the action of pressure.When it reaches the maximum experimental pressure value of29.4GPa,the photocurrent of ReS₂reaches nearly 400 times of that under the initial pressure,its photoelectric response in the infrared band has also been improved.The increase of photoelectric performance under pressure may be related to the increase of carrier concentration and mobility.These results indicate that pressure can significantly improve the photoelectric response of ReS₂,which provides the possibility for further regulating the photoelectric performance of TMDs system.