Electronic structure, phase stability, equation of state, and pressure-dependent superconducting properties of Zr3Al.

Abstract

We report here the ambient and high-pressure electronic-structure calculations of the potentially important ordered intermetallic alloy ${\mathrm{Zr}}_{3}$Al obtained using the self-consistent linear muffin-tin orbitals (LMTO) method. Further total-energy calculations were made using the tight-binding LMTO scheme in the ${\mathit{L}}_{12}$ and ${\mathit{DO}}_{19}$ phases in order to study its structural stability. From total-energy studies and the band filling of bonding states results, we conclude that it is easier to create instability in the ${\mathit{L}}_{12}$ lattice of ${\mathrm{Zr}}_{3}$Al and this prediction is consistent with the experimentally observed martensitic structural transition from ${\mathit{DO}}_{19}$\ensuremath{\rightarrow}${\mathit{L}}_{12}$ structure. To make a comparative study, the band structure and total-energy calculations of isoelectronic ${\mathrm{Ti}}_{3}$Al were also made. The calculated bulk modulus and its pressure derivative, determined using a universal equation of state, are reported. The nature of chemical bonding in ${\mathrm{Zr}}_{3}$Al is also discussed. Using the band-structure results, within the BCS formalism, the superconducting transition temperature (${\mathit{T}}_{\mathit{c}}$) was calculated and it is compared with the experimental value. The ambient-pressure band-structure, and ${\mathit{T}}_{\mathit{c}}$ calculations of the A15 compound ${\mathrm{Nb}}_{3}$Al were made with a view to compare its superconducting behavior with that of ${\mathrm{Zr}}_{3}$Al at high pressures as ${\mathrm{Zr}}_{3}$Al should mimic ${\mathrm{Nb}}_{3}$Al at high pressures. The pressure dependence of ${\mathit{T}}_{\mathit{c}}$ of ${\mathrm{Zr}}_{3}$Al is analyzed. Our calculations on ${\mathrm{Zr}}_{3}$Al are in contradiction with the often quoted correlation between the low density of states at the Fermi level and structural stability in similar systems and this is further corroborated with our more recent studies on ${\mathrm{Ti}}_{3}$In and ${\mathrm{Ni}}_{3}$In.