Melting of tantalum at high pressure determined by angle dispersive x-ray diffraction in a double-sided laser-heated diamond-anvil cell

The high-pressure and high-temperature phase diagram of Ta has been studied in a laser-heated diamond-anvil cell (DAC) using x-ray diffraction measurements up to 52 GPa and 3800 K. The melting was observed at nine different pressures, the melting temperature being in good agreement with previous laser-heated DAC experiments, but in contradiction with several theoretical calculations and previous piston-cylinder apparatus experiments. A small slope for the melting curve of Ta is estimated (dT(M)/dP approximate to 24 K GPa(-1) at 1 bar) and a possible explanation for this behaviour is given. Finally, a P-V-T equation of states is obtained, the temperature dependence of the thermal expansion coefficient and the bulk modulus being estimated.