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

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 K_S0 = 193.9(29) GPa, G₀ = 69.3(10) GPa, K_S0′ = 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 V_S 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.