In-situ x-ray study of the thermal expansion of iron at multimegabar pressure

The density of epsilon-iron was determined as a function of pressure, p, and temperature, T, at pressures up to 240 GPa and at temperatures ranging up to 1285 K by means of an externally electrically heated diamond anvil cell and in-situ x-ray powder diffraction with an area detector. On the basis of the experimental data the thermal equation of state of epsilon-iron was derived. The average thermal expansivity, <(alpha)over bar> = ln(V-T/V-300)/T - 300, of epsilon-iron for 200 GPa and 5000 K, where V is the molar volume, is 1.3 x 10(-5) K-1 and it is close to the value obtained in shock compression measurements and theoretical calculations.