Anomalous elastic behavior of tantalum at high pressures: Experimental and theoretical studies

Abstract

Elastic wave velocities of polycrystalline tantalum have been measured up to 13.6 GPa at room temperature using ultrasonic interferometry technique in a multi-anvil apparatus. The bulk and shear moduli, as well as their pressure derivatives are obtained using Eulerian 3rd order finite strain equations, yielding KS0 = 193.9(29) GPa, G0 = 69.3(10) GPa, KS0′ = 3.18(5) and G0′ = 0.88(1). The Steinberg-Guinan yield stress model is examined using the current shear modulus and its pressure derivative, where a slightly lower A0 = 0.0127 GPa−1 compared to previous studies is obtained. First-principles calculations on the elasticity of tantalum have also been performed up to 200 GPa. Anomalous softening of the elastic shear constant C44 and shear wave velocity VS is observed between 80– 180 GPa, whereas the anisotropy shows a softening-stiffening behavior with increasing pressure and reaches a minimum at around 150 GPa. Such anomalies might commonly originate from the nesting of Fermi surface for Group VB metals.