EPR studies on local structure of 70V₂O₅-30P₂O₅ glass at 4K

Abstract

From the obtained spin-Hamiltonian parameters of the axially symmetric lineshape of the glass at 4K it is concluded that the paramagnetic site in the glass is vanadyl ion, VO²⁺. The vanadium is in distorted octahedral environment of six oxygens forming a O- VO₄..O unit. This geometry of <i>C_4v</i> symmetry leads to the value of the coefficient of 3<i>d_xy </i> orbital <i>β</i><img src='http://www.niscair.res.in/jinfo/plustwo.gif' border=0> as 0.96 and the Fermi contact term <b><i><img src='/image/spc_char/k.gif' border=0></i></b> the measure of the vanadium 4sorbital contribution to bonding as 0.75. The crystal field splitting energy, tetragonal distortion energy and spin-orbit coupling constant are found to be 23186, 12056 and 169 cm^-1, respectively. From the above values, it is concluded that O- VO₄_•••O unit has highly 'squeezed' VO₄ group with moderate axial compression. The vanadium <i>3d¹ </i> small polaron gets localized on a ⁵¹<i>V</i>(<i>I</i>= 7/2)site at <b><i>4s </i></b> due to the 'Anderson localization' and thereby the symmetry of the local structure of the glass is reflected in its EPR lineshape.