Effects of Al doping on the structural and electronic properties of Mg1-xAlxB2 -: art. no. 012511

We have studied the structural and electronic properties of Mg1-xAlxB2 within the virtual crystal approximation (VCA) by means of first-principles total-energy calculations. Results for the lattice parameters, the electronic band structure, and the Fermi surface as a function of Al doping for 0less than or equal toxless than or equal to0.6 are presented. The ab initio VCA calculations are in excellent agreement with the experimentally observed change in the lattice parameters of Al-doped MgB2. The calculations show that the Fermi surface associated with holes at the boron planes collapses gradually with aluminum doping, and vanishes for x=0.56. In addition, an abrupt topological change in the sigma-band Fermi surface was found for x=0.3. The calculated hole density correlates closely with existing experimental data for T-c(x), indicating that the observed loss of superconductivity in Mg1-xAlxB2 is a result of hole band filling.