Sound velocity measurements of tantalum under shock compression in the   10-110 GPa range
  The high-pressure melting curve of tantalum (Ta) has been the center of a long-standing controversy. Sound velocities along the Hugoniot curve are expected to help in understanding this issue. To that end, we employed a direct-reverse impact technique and velocity interferometry to determine sound velocities of Ta under shock compression in the 10-110 GPa pressure range. The measured longitudinal sound velocities show an obvious kink at ~60 GPa as a function of shock pressure, while the bulk sound velocities show no discontinuity. Such observation could result from a structural transformation associated with a negligible volume change or an electronic topological transition. 
Jianbo Hu, Chengda Dai, Yuying Yu, Zijiang Liu, Ye Tan, Xianming Zhou,   Hua Tan, Lingcang Cai, Qiang wu
cond-mat.mtrl-sci