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The stability of high-entropy alloys (HEAs) is a key issue before their selection for industrial applications. In this study, in-situ high-pressure and high-temperature synchrotron radiation X-ray diffraction experiments have been performed on three typical HEAs Ni20Co20Fe20Mn20Cr20, Hf25Nb25Zr25Ti25, and Re25Ru25Co25Fe25 (at. %), having face-centered cubic (fcc), body-centered cubic (bcc), and hexagonal close-packed (hcp) crystal structures, respectively, up to the pressure of ~80 GPa and temperature of ~1262 K. Under the extreme conditions of the pressure and temperature, all three studied HEAs remain stable up to the maximum pressure and temperatures achieved. For these three types of studied HEAs, the pressure-dependence of the volume can be well described with the third order Birch-Murnaghan equation of state. The bulk modulus and its pressure derivative are found to be 88.3 GPa and 4 for bcc-Hf25Nb25Zr25Ti25, 193.9 GPa and 5.9 for fcc-Ni20Co20Fe20Mn20Cr20, and 304.6 GPa and 3.8 for hcp-Re25Ru25Co25Fe25 HEAs, respectively. The thermal expansion coefficient for the three studied HEAs is found to be in the order as follows: fcc-Ni20Co20Fe20Mn20Cr20>bcc-Hf25Nb25Zr25Ti25 ≈hcp-Re25Ru25Co25Fe25. [ABSTRACT FROM AUTHOR]

As-cast amorphous AsSe (a-AsSe) has been characterized by in-situ high pressure XRD and Raman spectroscopy up to the pressure of ~30GPa using diamond anvil cell together with ab-initio molecular dynamics simulations. A gradual densification has been observed under compression along with the breakdown of intermediate range ordering at ~16GPa. The whole transformation process can be divided into three relatively distinct pressure regimes from 1 bar to 7GPa, from 7 to 16GPa, and beyond 16GPa. Our XRD results together with Raman spectroscopic studies confirm that in the a-AsSe pressure tuning results in network transformations only, without sudden jump in the density. The results obtained by high pressure ab-initio molecular dynamics simulations demonstrate the variations in the local structures associated with the experimentally observed transformations. The amorphous-to-amorphous network transformation is found to be reversible upon decompression. [ABSTRACT FROM AUTHOR]