P–V–T Equation of State of Iridium Up to 80 GPa and 3100 K

Abstract

In the present study, the high-pressure high-temperature equation of the state of iridium has been determined through a combination of in situ synchrotron X-ray diffraction experiments using laser-heating diamond-anvil cells (up to 48 GPa and 3100 K) and density-functional theory calculations (up to 80 GPa and 3000 K). The melting temperature of iridium at 40 GPa was also determined experimentally as being 4260 (200) K. The results obtained with the two different methods are fully consistent and agree with previous thermal expansion studies performed at ambient pressure. The resulting thermal equation of state can be described using a third-order Birch–Murnaghan formalism with a Berman thermal-expansion model. The present equation of the state of iridium can be used as a reliable primary pressure standard for static experiments up to 80 GPa and 3100 K. A comparison with gold, copper, platinum, niobium, rhenium, tantalum, and osmium is also presented. On top of that, the radial-distribution function of liquid iridium has been determined from experiments and calculations.

Characterization of the high-pressure and high-temperature phase diagram and equation of state of chromium

“…1 a,b together with the patterns obtained at T just below and above 3007 K. In particular, it is possible to observe how, at this T , the (110) and (211) reflections of bcc -Cr disappear whilst a diffuse XRD signal appears close to where the previous (110) reflection was located. Such a phenomenon is usually correlated to melting of transition metals 18 , 22 – 24 , therefore it is very reasonable to correlate it to the formation of liquid Cr. A further T increase causes the appearance of an additional (and more intense) diffuse signal, the center of which is shifted towards lower angles.…”

“…For this purpose, the samples were prepared following a similar procedure to the one used for the aforementioned experiments performed at Diamond Light Source, but instead using MgO as the insulating material (to exclude any effects caused by the melting of KBr). As for the experiments performed on beamline I15, T was measured via spectral-radiometry, whereas P was measured from ruby fluorescence method at 300 K. The thermal P was estimated by comparison with similar data from a previous XRD experiment performed using MgO as the insulating material 22 . The temperatures obtained for the plateaus in these ramps are (3500 ± 150) K and (4000 ± 150) K at (55 ± 5) GPa and (90 ± 5) GPa, respectively.…”

“…In particular, considerable effort has been devoted to trying to solve the discrepancies observed in the extreme cases of Fe 2 – 11 , Ta 12 – 14 , Mo 15 – 17 and Pt 18 – 21 . The melting curves of other transition metals, like Nb, Ir, and V have also been studied recently 22 – 24 .…”

Unusual Force Constants Guided Distortion-Triggered Loss of Long-Range Order in Phase Change Materials

“…When the magnitude of distortion is larger than 0.17 Å, the bond initially featuring strong FCs will become longer than the bond initially featuring weak FCs, leading to the exchange of the relative strong and weak characteristics of FCs, namely, the initial stronger bonds become weaker and the initial weaker bonds become stronger. The distorted structures are then deployed into MD simulations to see whether these locally disturbed crystalline structures can become amorphous without initially presetting very high temperature in MD simulations [57]. The obtained pair correlation function, or radial distribution function (RDF) g(r) for different distortions is shown in Figure 9.…”

Properties of Transition Metals and Their Compounds at Extreme Conditions

“…In the subsequent contribution, Anzellini et al [6] reported the first experimental characterisation of the phase diagram of iridium obtained with a combination of a laserheated diamond anvil cell with synchrotron X-ray diffraction and density-functional theory calculations. Together with the solid and liquid phase boundary of iridium, the authors also report the corresponding thermal equation of state and compare it with the one of other transition metals.…”