Structural instabilities and mechanical properties of U2Mo from first principles calculations

Abstract

We perform detailed first principles calculations of the structural parameters at zero pressure and high pressure, the elastic properties, phonon dispersion relation, and ideal strengths of U₂Mo with the C11_b structure. In contrast to previous theoretical studies, we show that the I4/mmm structure is indeed a mechanically and dynamically unstable phase, which is confirmed by the negative elastic constant C₆₆ as well as the imaginary phonon modes observed along the Σ₁–N–P line. The calculations of ideal strengths for U₂Mo are performed along the [100], [001], and [110] directions for tension and on (001)[010] and (010)[100] slip systems for shear load. The ideal shear strength is about 8.1 GPa, much smaller than a tension of 18–28 GPa, which indicates that the ductile U₂Mo alloy will fail by shear rather than by tension.