Breakdown of intermediate range order in AsSe chalcogenide glass

As-cast amorphous AsSe (a-AsSe) has been characterized by in-situ high pressure XRD and Raman spectroscopy up to the pressure of ∼30 GPa 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 ∼16 GPa. The whole transformation process can be divided into three relatively distinct pressure regimes from 1 bar to 7 GPa, from 7 to 16 GPa, and beyond 16 GPa. 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

Structural stability of high entropy alloys under pressure and temperature

The stability of high-entropy alloys (HEAs) is a key issue before their selection for industrial appli-cations. In this study,in-situhigh-pressure and high-temperature synchrotron radiation X-raydiffraction experiments have been performed on three typical HEAs Ni$_{20}$Co$_{20}$Fe$_{20}$Mn$_{20}$Cr$_{20}$,Hf$_{25}$Nb$_{25}$Zr$_{25}$Ti$_{25}$, and Re$_{25}$Ru$_{25}$Co$_{25}$Fe$_{25}$(at. %), having face-centered cubic (fcc), body-centeredcubic (bcc), and hexagonal close-packed (hcp) crystal structures, respectively, up to the pressure of80 GPa and temperature of1262 K. Under the extreme conditions of the pressure and tempera-ture, 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 welldescribed with the third order Birch-Murnaghan equation of state. The bulk modulus and itspressure derivative are found to be 88.3 GPa and 4 for bcc-Hf$_{25}$Nb$_{25}$Zr$_{25}$Ti$_{25}$, 193.9 GPa and5.9 for fcc-Ni$_{20}$Co$_{20}$Fe$_{20}$Mn$_{20}$Cr$_{20}$, and 304.6 GPa and 3.8 for hcp-Re25Ru25Co25Fe25HEAs,respectively. The thermal expansion coefficient for the three studied HEAs is found to be in theorder as follows: fcc-Ni$_{20}$Co$_{20}$Fe$_{20}$Mn$_{20}$Cr$_{20}$ > bcc-Hf$_{25}$Nb$_{25}$Zr$_{25}$Ti$_{25}$hcp-Re$_{25}$Ru$_{25}$Co$_{25}$Fe$_{25}$

Structural stability of high entropy alloys under pressure and temperature

The stability of high-entropy alloys (HEAs) is a key issue before their selection for industrial appli-cations. In this study,in-situhigh-pressure and high-temperature synchrotron radiation X-raydiffraction experiments have been performed on three typical HEAs Ni$_{20}$Co$_{20}$Fe$_{20}$Mn$_{20}$Cr$_{20}$,Hf$_{25}$Nb$_{25}$Zr$_{25}$Ti$_{25}$, and Re$_{25}$Ru$_{25}$Co$_{25}$Fe$_{25}$(at. %), having face-centered cubic (fcc), body-centeredcubic (bcc), and hexagonal close-packed (hcp) crystal structures, respectively, up to the pressure of80 GPa and temperature of1262 K. Under the extreme conditions of the pressure and tempera-ture, 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 welldescribed with the third order Birch-Murnaghan equation of state. The bulk modulus and itspressure derivative are found to be 88.3 GPa and 4 for bcc-Hf$_{25}$Nb$_{25}$Zr$_{25}$Ti$_{25}$, 193.9 GPa and5.9 for fcc-Ni$_{20}$Co$_{20}$Fe$_{20}$Mn$_{20}$Cr$_{20}$, and 304.6 GPa and 3.8 for hcp-Re25Ru25Co25Fe25HEAs,respectively. The thermal expansion coefficient for the three studied HEAs is found to be in theorder as follows: fcc-Ni$_{20}$Co$_{20}$Fe$_{20}$Mn$_{20}$Cr$_{20}$ > bcc-Hf$_{25}$Nb$_{25}$Zr$_{25}$Ti$_{25}$hcp-Re$_{25}$Ru$_{25}$Co$_{25}$Fe$_{25}$