Unusual mechanical strengths of Ta2O5 stable phases: A first-principles calculation study

Abstract

Tantalum, in its most stable Ta2O5 oxide form, has long been recognized as a superior coating material in orthopedic applications. In this study, the ideal mechanical strengths of I41/amd, Cmmm, C2/c, Pm, and Pbam phases of Ta2O5 are investigated from first-principles calculation, where the stress–strain curves under various deformation strains are obtained and the structural evolution in terms of atomic bonding is analyzed. The results reveal that these stable Ta2O5 polymorphs show unusual mechanical strengths on their high symmetric crystalline planes. Shear super-plasticity is found on the (001) crystalline plane of the I41/amd phase in any shear direction. Shear strain-stiffening exists on the (100) crystalline plane of the Pm phase in the shear direction within an angle of ±18° along the [001] direction. Both shear super-plasticity and shear strain-stiffening make these crystalline planes be able to sustain excessively large shear deformations. Large and isotropic shear strengths are predicted on the (010) crystalline planes of Pm and Pbam phases with nearly identical maximum and minimum peak shear stresses approaching 15 GPa. Much stronger compression and tensile strengths are obtained normal to the (010) crystalline plane of the C2/c phase due to its special spring-like bonding structure, which can endure the compression deformation up to 30%. These findings provide guidance for selecting suitable phases of Ta2O5 and growth directions with crystalline planes possessing excellent mechanical properties in applications of Ta2O5 as a coating material on Ti alloys for biomedical replacements of damaged human organs, such as hip joints, dental implants, and artificial hearts.