Ruby, metals, and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>MgO</mml:mi></mml:mrow></mml:math>as alternative pressure scales: A semiempirical description of shock-wave, ultrasonic, x-ray, and thermochemical data at high temperatures and pressures

Abstract

We have constructed semiempirical equations of state of Al, Au, Cu, Pt, Ta, and W, which within experimental error bars describe the available shock-wave, ultrasonic, x-ray, and thermochemical data in the temperature range from $10--20\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ up to the melting temperature and to compression $x=V∕{V}_{0}=0.5--0.7$. The comparison of the calculated room-temperature isotherms for these metals with quasihydrostatic measurements supports recently proposed ruby pressure scales. We recommend a new ruby pressure scale in the form $P=A(\mathrm{\ensuremath{\Delta}}\ensuremath{\lambda}∕{\ensuremath{\lambda}}_{0})\ifmmode\times\else\texttimes\fi{}(1+m\mathrm{\ensuremath{\Delta}}\ensuremath{\lambda}∕{\ensuremath{\lambda}}_{0})$ with parameters $A=1884\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ and $m=5.5$. The cross check on independent data confirms the obtained PVT equations of state of Ag, Al, Au, Cu, Pt, Ta, W, $\mathrm{MgO}$, and diamond. The equations of state of these materials obtained here provide accurate and versatile means for calibrating pressure at all temperatures below the melting point. Furthermore, they can be used for accurate tabulation of thermodynamic properties (heat capacities, entropies) of these reference substances in a wide P-T range.