Correction of the pressure scales reliant to the thermal pressures shifts in iron (3d) vanadium (4d), iridium and platinum (5d) transition metals

Abstract

In many published articles isobaric behavior in DAC chambers has been reported On the other hand, a clear isochoric behavior in the chambers were reported. Thus, Isochoric or isobaric condition remain an open question. In isochoric condition, upon increasing the temperature, at each pressure, the examined sample and the PTM both are subject to increases of their volumes which is suppressed by the chamber finite volume, provoking an increase in the thermal pressure over the whole system. For this reason, the pressure scale reported in DAC experiments do not represent the actual pressure experienced by the sample in the cell. The different response of the PTMs to P,T changes is the reason for the variety of melting curves reported in the literature. It is concluded that the pressure scale in DAC experiments need a correction taking in to account the thermal pressure shift. Trusting the first principals DFT- Z methodology it is shown that the melting curve derived by this method should serve as an anchor for the pressure scale correction.