摘要
A 4:1(volume ratio)methanol–ethanol(ME)mixture and silicone oil are two of the most widely used liquid pressure-transmitting media(PTM)in high-pressure studies.Their hydrostatic limits have been extensively studied using various methods;however,the evolution of the atomic structures associated with their emerging nonhydrostaticity remains unclear.Here,we monitor their structures as functions of pressure up to∼30 GPa at room temperature using in situ high-pressure synchrotron x-ray diffraction(XRD),optical micro-Raman spectroscopy,and ruby fluorescence spectroscopy in a diamond anvil cell.No crystallization is observed for either PTM.The pressure dependence of the principal diffraction peak position and width indicates the existence of a glass transition in the 4:1MEmixture at∼12 GPa and in the silicone oil at∼3 GPa,beyond which a pressure gradient emerges and grows quickly with pressure.There may be another liquid-to-liquid transition in the 4:1 ME mixture at∼5 GPa and two more glass-to-glass transitions in the silicone oil at∼10 GPa and∼16 GPa.By contrast,Raman signals only show peak weakening and broadening for typical structural disordering,and Raman spectroscopy seems to be less sensitive than XRD in catching these structural transitions related to hydrostaticity variations in both PTM.These results uncover rich pressure-induced transitions in the two PTM and clarify their effects on hydrostaticity with direct structural evidence.The high-pressure XRD and Raman data on the two PTM obtained in this work could also be helpful in distinguishing between signals from samples and those from PTM in future high-pressure experiments.
基金
supported by the National Natural Science Foundation of China(Grant Nos.51871054 and U1930401)
The XRD experiments were performed on beamline 15U1 of the Shanghai Synchrotron Radiation Facility(SSRF)and on beamline 13 ID-D of GSECARS at the Advanced Photon Source(APS),Argonne National Laboratory(ANL),USA
The use of beamline 13-ID-D at the APS was supported by the National Science Foundation(NSF)–Earth Sciences(Grant No.EAR-1634415)
the Department of Energy(DOE)–GeoSciences(GrantNo.DEFG02-94ER14466)
supported by the DOE Office of Science(Grant No.DE-AC02-06CH11357).
