ELECTRON-PARAMAGNETIC-RESONANCE OF FE-3- COMPUTER-SIMULATIONS( IONS IN BORATE GLASS )

Computer simulations of Fe3+ electron paramagnetic resonance spectra a t X (9.5 GHz) and Q (34 GHz) bands in the alkali borate glass Li2O-2B2 O3 doped with Fe2O3 have been carried out using an approach based on t he eigenfield method applied to the 'rhombic' spin Hamiltonian, which contains only the Zeeman and quadrupole fine-structure terms. In order to account for the structural disorder in the glass, two different di stribution densities of fine-structure parameters D and E have been tr ied: a two-dimensional Gaussian function of D and lambda = \E/D\, and the 'Czjzek function', analogous to the one used in Mossbauer-effect s tudies. In simulating the experimental spectra, care has been taken to fit not only to the most prominent features arising at g(ef) congruen t-to 4.3 (at X and Q bands) and g(ef) congruent-to 2.0 (at Q band), bu t also to an obvious plateau of the derivative of the absorption, whic h extends down to the magnetic field corresponding to g(ef) congruent- to 9.7 (at both bands). As a result, the Czjzek function can be ruled out. The agreement between the experimental and computer-simulated spe ctra found with the Gaussian distribution density suggests the existen ce, besides orthorhombic symmetry sites (with lambda congruent-to 1/3) , of a considerable number of Fe3+ sites with axial or feebly rhombic distortions (lambda less-than-or-equal-to 0.08). The relatively high m ean value of the axial fine-structure parameter D is consistent with a highly distorted environment of Fe3+ ions in the glass.