144 / 2023-04-14 19:40:11

Crystal Structure and Melting Curve of Tantalum under High Pressure

shock melting,crystal structure of tantalum,in situ x-ray diffraction,equation of state,laser driven high pressure

高压物理与材料科学 > 动高压-II

Since tantalum is utilized as an experimental benchmark to accurately determining the sample pressure at high energy density conditions, the equation of state of tantalum is of great important. The melting curve of tantalum is a fundamental issue in equation of state investigation. As a transition metal, the partially filled 5d-electron subshell could significantly alter the valence electron interactions and distribution. Therefore, the melting behavior of tantalum complexed which remains irreconcilable and inconclusive. It’s a great scientific challenge on both experimental measurements and theoretical predictions. Although a plethora of static [1,2,5] and dynamic compression [3,4,6] experiments and corresponding theoretical work [7,8,9,10,11], the melting transition of tantalum disperse at high pressure remains poorly constrained and the crystal structure beyond 150GPa / 300K up to the melt boundary is still not unambiguously determined. In this work, we carried out in-situ X-ray diffraction measurements in laser driven shock compressed tantalum that establish the stability of the body centered cubic structure along the Hugoniot on sub-nanosecond time scale. The observation of shock melting of tantalum started between 240.3 and 269.9 GPa and completed between 318.1 and 355.5 GPa. Since temperature was unable to be directly measured in this work, we use the experiment data as constraint to calculate the melting curve of tantalum up to 450GPa by ab initio molecular dynamics, which combines the advantages of the two-phase method and the modified-Z method [12]. Here we compare our melting curve with other experimental and theoretical data. Our results consistent with reported shock wave experiment within ~5% error, however, deviated from static melting data with ~15% under high pressure. The discrepancies between static and dynamic compression still irreconciled. This phenomenon might originate from unrevealed technical or physical issue. Therefore, we will discuss the reasons which could causing this discrepancy in this report.