Sound velocity and equation of state in liquid cesium at high pressure and high temperature

Abstract

Liquid cesium (l-Cs) sound velocity at high densities was investigated along a 500 K isotherm using high-pressure picosecond acoustics measurements. At 2.0 GPa, the liquid sound velocity goes through a maximum versus pressure without any change on the reflectivity and interferometry acoustic signals. Upon further compression, a softening of the l-Cs visco-elastic properties is observed from 2.0 up to 4.0 GPa, pressure at which the reflectometric signal is abruptly reversed whereas the interferometric signal remains qualitatively the same. This anomalous behaviour could be related to an electronic transformation within the l-Cs state, which here again could reflect what happens at lower temperature within the solid state. If so, such liquid-liquid transition may be driven by the progressive collapse of the 6s electronic orbital onto the 5d ones. Above 4.0 GPa, the l-Cs sound velocity starts again to increase as commonly expected upon compression.

Non‐Bonded Radii of the Atoms Under Compression

“…d‐occupation in Cs is one acknowledged driver for low symmetry crystal structures and high‐pressure phase transitions [141–143] . There are also disputed claims of a first‐order phase transitions in liquid Cs driven by 6s→5d electron transfer [144–148] . Our calculations on atomic Cs predict the 6s→5d configurational transition to occur at ∼25 GPa and correspond to a radial contraction of 0.10 Å (Figure 7).…”

A Review of the Melting Curves of Transition Metals at High Pressures Using Static Compression Techniques

“…For most metals, the density of the liquid is lower than that of the solid, while the entropy is higher, leading to mostly positive melting slopes (i.e., the melting temperature increases with pressure) [16,22,24,29,[35][36][37]39,40,63]. The situation is much more intricate for alkali metals, however, whose phase diagrams reveal complex liquid melting-curve maxima and negative melting slopes [64][65][66][67][68][69], since these elements exhibit several density discontinuities and phase transitions already in the solid phase. In this case, the Kechin equation is more appropriate to describe the melting curve [70].…”

“…The melting curves of alkali metals behave rather differently than those of transition metals. These elements tend to have complex phase diagrams, with successive phase transitions in the solid phase and the presence of complex liquids in the liquid phase [64][65][66][67][68][69]95]. In many cases, alkali metals exhibit melting curve maxima, followed by negative slopes, where the molar volume of the liquid is expected to be less than that of the solid.…”

“…Resistive heating methods have been extensively used to study the melting behavior and phase diagrams of alkali metals [64][65][66]68,69] and molecular systems [144][145][146][147], which generally have much lower melting temperatures than transition metals. The pressure range in an RH-DAC is limited compared to the LH-DAC, often because of the softening of the stress-bearing components, such as the gaskets and the diamond seats.…”

Термодинамические Свойства Жидкого Цезия: Поиск Аномалий

“…В то же время появление различных аномалий в виде экстремумов на изолиниях свойств вполне возможно. Например, для жидкого цезия в эксперименте зафиксирован максимум скорости звука u max на изотерме 500 K при давлении ∼ 2 GPa [40], и задача заключается в том, чтобы построить (p, T ) u -линию в широком интервале параметров, как это сделано для максимумов плотности воды в нормальном и метастабильном состояниях [41].…”