Structural, electronic and magnetic properties of V2O5-x: An ab initio study

Pure V2O5 is a diamagnetic layered semiconductor with many applications such as catalysis. In this paper, we study oxygen vacancy-induced changes in the atomic and electronic structures as well as magnetic properties of V2O5-x within spin density functional theory with generalized gradient approximation. Both the supercell approach and virtual crystal approximation are used to simulate the oxygen-deficient V2O5-x with vacancy concentration x up to 0.5. The 1x2x2 supercell calculations with one O vacancy predict that the formation energies of the apical (O-1), bridge (O-2), and chain (O-3) oxygen vacancies are, respectively, 2.48, 4.17, and 4.44 eV/vacancy, and hence that the O vacancies in V2O5-x would be predominantly of the O-1 type. The local structural distortions of the V atoms next to the O vacancies are found to be large for high vacancy density x(x>0.25), and for x similar to 0.5, even the crystal lattice changes from the orthorhombic to monoclinic symmetry. In all the cases considered, an O vacancy-induced stable or metastable ferromagnetic state with spin magnetic moment of similar to 2.0 mu(B)/vacancy is found. For x below similar to 0.13 and 0.19 < x <= 0.5, the antiferromagnetic state with the V spins on neighboring rungs (AF-2) being antiparallel is the ground state. Importantly, this suggests that undoped V2O5-x with x <= 0.13 and 0.19 < x