An EPR and Optical Absorption Study of VO2+ Ions in Di-Ammonium Hydrogen Citrate [(NH4)2C6H6O7] Single Crystals

Abstract

Single crystal and powder EPR studies of VO2+ doped di-ammonium hydrogen citrate [(NH<inf>4</inf>)<inf>2</inf>C<inf>6</inf>H<inf>6</inf>O<inf>7</inf>] are carried out at room temperature. The angular variation of the EPR spectra show three different VO2+ complexes that are located in different chemical environment, and each environment contains two magnetically inequivalent VO2+ sites in distinct orientations occupying substitutional positions in the lattice. Crystalline field around the VO2+ ion is nearly axial. The optical absorption spectrum shows two bands centred at 16,949 and 12,345 cm-1. Spin Hamiltonian parameters and molecular orbital coefficients are calculated from the EPR and optical data, and results are discussed. © 2007.