Establishment Of The Method For Measuring Resistance Under Dynamic Loading And The Phase Transitions Of Chalcogenide Under High Pressure

High-pressure experimental technology can be divided into two major fields:static pressure and dynamic pressure,according to the different loading modes.As a complement of these technologies,various dynamic loading devices have been developed for controlling pressure and compression/decompression rates.In this dissertation,based on the dynamic loading device and the experimental technique of diamond anvil cells?DACs?,the experimental method for measuring resistance under dynamic compression was established and the phase transitions of chalcogenide under static high pressure were investigated.In this paper,the challenges of the preparation for the microcircuit on the DAC surface have been overcome by the combination of the magnetron sputtering technology and DAC technology.And based on the dynamic loading device,we can obtain the voltage signals during the dynamic compression.Subsequently,we complete the establishment of the method for measuring resistance under dynamic loading.Based on the diffraction and resistance measurements of PbS under different compression rates,the reliability and practicability of the system have been verified.We have found that the different loading rates can change the proportion between the two intermediates generated by the first phase transtion of PbS.The pressure-induced structural transitions of ZnTe have been investigated at pressures up to 60 GPa under different hydrostatic conditions using synchrotron X-ray diffraction?XRD?and first principles calculations.A phase transition from the initial zinc blende structure to an intermediate phase was observed at about 9 GPa,followed by another phase transition at about 12 GPa.Based on Rietveld refinement and calculations,the intermediate phase is determined to have a cinnabar structure,while the second high pressure phase is an orthorhombic structure with Cmcm symmetry.Then by theoretical calculations,we find that the absence of the NaCl?B1 phase?structure under high pressure in ZnTe is related to the atomic coordinates of the cinnabar phase.Based on synchrotron powder XRD,high-pressure Roman scattering measurements and ab initio calculations,the structural phase transition sequence of GeTe has been investigated at pressures up to 60 GPa.The R3m structure is stable in GeTe at ambient conditions.To further check the phase transition from R3m to B1,we perform the Rietveld analysis,and find that the spurious transformation from R3m to B1 is due to the changes of the difference in the compression ratio of lattice parameters for the R3m phase.As pressure is increased to about 17 GPa,the initial R3m phase transforms into a Pnma phase.The pressure-induced structural transitions of Bi₂Te_xSe_3-x?X=0,1,2?have been investigated under hydrostatic conditions using synchrotron XRD and theoretical calculations.These compounds adopt a rhombohedral structure at ambient conditions.Upon compression,we demonstrated that the ambient R???m phase of Bi₂Se₃ crystallized into a C2/m phase at 9.1 GPa,and eventuallyto a body-centered tetragonal structure with the space group I4/mmm at about 27.2 GPa.In the decompression process,Bi₂Se₃becomes an amorphous solid with serious crystal lattice distortions.Based on Rietveld refinements,both Bi₂Te₂Se and Bi₂Se₂Te follow the structural phase transition sequence of R???m?C2/m?C2/c?CsCl?B2?.Bi₂Te_xSe_3-x?X=1,2?undergo the similar structural phase transitions to Bi₂Te₃ by doping Te in Se sites.The pressure-induced structural transitions of Sb₂Se₃ have been investigated under different hydrostatic conditions using synchrotron XRD,resistance measurement experiment and theoretical calculations.The orthorhombic structure with a space group Pnma is stable in Sb₂Se₃ at ambient conditions.As pressure was increased to 30 GPa,a broadening peak originate from structural disorder emerges.Eventually,Sb₂Se₃ transforms into a site-disorder Im???m phase above 50 GPa.During decompression,Sb₂Se₃ becomes an amorphous solid,caused by the differencein electronegativity between Sb and Se.The pressure-induced phase transitions of Sb₂Se₃ have been further confirmed by the resistance measurement.