Anharmonicity and the equation of state for gold

摘要

The temperature dependence of the thermodynamic and the elastic properties of elemental gold are found from published data. It is shown that measurements for (part;KT/part;P)Tnear 5.5 are more thermodynamically consistent than are higher values of this parameter which have been reported earlier. Using 5.5 for (part;KT/part;P)T, we find that (part;KT/part;T)Vis not zero but minus;11.5times;10minus;3GPathinsp;Kminus;1for high temperatures (Tthgr;D, where thgr;Dis the Debye temperature). One consequence of this is that above thgr;Dthe thermal pressure,PTH, along the roomhyphen;pressure isobar can be expressed asPTH(T)minus;PTH(300)=lsqb;7.14times;10minus;3+(part;KT/part;T)vthinsp;ln(Va/V)rsqb; times;(Tminus;300) GPa forTat absolute temperature andVabeing the volume at ambient conditions. These results give thermal pressure values near those previously reported at small compressions, but give lower thermal pressures at large compressions. This study suggests that in order to ensure thermodynamic consistency, the value ofdthinsp;lnthinsp;ggr;/dthinsp;lnthinsp;Vis near 2.5ndash;3.0 which is higher than values of 1.0 and 1.7 reported previously (ggr; is the Gruuml;neisen ratio). Calculations giving the compressional and shear wave velocities,vpandvs, are also presented. One result is that the quantity part;thinsp;lnthinsp;vs/part;thinsp;lnthinsp;vpat constant pressure is about 1.85 and is independent of temperature.