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.
Highlights
Iridium (Ir) belongs to the family of the 5d transition metals
In the investigated P–T range, only peaks belonging to f cc Ir and magnesium oxide (MgO) were observed with no evidence of any solid–solid phase transitions or chemical reactions
The texture of both MgO and Ir showed a similar temperature-induced evolution, starting with a high quality powder averaging at 300 K and showing increased recrystallization with the raising T
Summary
Iridium (Ir) belongs to the family of the 5d transition metals. It exhibits a face-centered cubic ( f cc) structure and its electronic structure is [Xe] 4 f 14 5d7 6s2. Thanks to its high shear modulus, chemical inertness, refractory nature, and phase stability, Ir is ideally suited as gasket material in static experiments in diamond-anvil cells (DAC) or as pressure standard for high-pressure (HP) experiments (in both static and dynamic experiments). As it exhibits excellent mechanical properties and high resistance to oxidation and corrosion at elevated temperature, Ir is used in numerous applications as a static component at high T and/or in aggressive environments. Ir is notably inert in comparison to other transition metals [1], and it is largely immune to chemical reactions in comparison to refractory metals such as rhenium [2] or tungsten [3]
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