| Pressure as an important thermodynamic means which can change the structure of materials,thereby changing the properties of electric transportation and optoelectronic properties of materials,and the progress of its technology has expanded the application of human beings in high-pressure research theory.In this paper,through combining with IR absorption spectroscopy,Raman spectroscopy,in-situ synchrotron radiation X-ray diffraction,alternative current impedance spectroscopy and photocurrent spectroscopy,the structure and electrical transport properties of the bowl-shaped cluster molecule C18Te3Br4（Bu-O）6 were systematically studied,and the structure and photoelectric properties of layered mixed valence tin oxide Sn3O4 were studied under high-pressure by using the diamond anvil cell.It was found that the pressure induced phase transition could change the physical properties of the material.The main research results obtained from the analysis of experimental results are as follows:1.Dehydro-Diders-Alder（DDA）reaction is a typical reaction for the preparation of sixmembered rings in solution,but it is rarely seen in solid synthesis.The results show that C18Te3Br4（Bu-O）6 might experience a DDA reaction at about 7 GPa,and the saturated sp3 bond carbon at the end of the molecule is decomposed into unsaturated sp2 bond carbon,that is,CH2-CH2-CH2-CH3 is decomposed into-CH2-CH2-CH=CH2,releasing hydrogen.According to the XRD results,the iron gasket absorbs some hydrogen atoms,reducing the phase transition pressure from bcc to hcp from 13 GPa to 9.7 GPa.Above 17.0 GPa,IR and Raman spectra show that the sample undergoes bond transition from intramolecular sp2 in molecular crystal into intermolecular sp3 in an amorphous carbon,indicating that pressure induced diamondization has occurred,forming a carbon network with high sp3 bond.In addition,a critical pressure of 45 GPa was observed.From the critical pressure below the pressure relief,the transition from the sp2 bond to the sp3 bond is not completely reversible.When the pressure is relieved above the critical pressure,it is observed that decompression-induced graphitization of glassy carbon.2.Combined with high pressure alternative current impedance spectroscopy,the effect of pressure on the electric transport properties of C18Te3Br4（Bu-O）6 was studied.In the lowpressure range,grain boundary conduction plays a dominant role in the electric transport of C18Te3Br4（Bu-O）6.When the pressure is above about 8 GPa,the grain resistance and grain boundary resistance decrease sharply,and the electric transport property changes from grain boundary dominant to grain dominant.After 20.2 GPa,the grain boundary effect disappears.After decompression,the grain resistance and grain boundary resistance almost recovered to the initial value,indicating that the recovered sample has a certain correlation with the original sample structure.The change in the properties of C18Te3Br4（Bu-O）6 electrical transport is due to the pressure-induced DDA reaction that changes the transport properties from grain boundary dominance to grain dominance and intramolecular sp2 bond to intermolecular sp3 bond conversion,resulting in a good carrier transport channel.This opens a new avenue for building crystalline carbon materials with different transport performance.3.The structure and photoelectric properties of layered mixed valence tin oxide Sn3O4 were studied by high-pressure Raman spectroscopy and photocurrent measurements.The change of lattice vibration mode of Sn3O4 were observed by Raman spectroscopy,and several new vibration mode peaks appeared at the pressure of 2.8 GPa,16.3 GPa and 28.9 GPa,respectively,indicating the structural phase transition.According to the photocurrent test results,from ambient to 2.2 GPa,the photocurrent of Sn3O4 increases and reaches the maximum value,indicating that more free carriers are generated.As the pressure increases,the photoelectric response of Sn3O4 decreases rapidly,possibly due to structural phase transitions leading to the generation of interfaces,which introduces carrier scattering and additional composite channels.When the pressure is above 15.8 GPa,the photoelectric response of Sn3O4 becomes weak and difficult to detect compared with the low pressure,which may be related to the pressure-induced structural phase transition.The experimental results show that pressure can significantly adjust the photoelectric performance of Sn3O4,which provides insights for the design of optoelectronic devices based on Sn3O4. |
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