MICROSCOPIC STRUCTURE OF DOPED BORATE GLASSES FROM MOLECULAR-DYNAMICS SIMULATIONS

The structure of four metal-halide-doped borate glasses (MX)x (M2O-2B2O3)1-x (M = Ag,Li; X = I,Cl) was calculated using molecular dynamics. Addition of AgI, x = 0.6, does not affect the local structure of the B-O network; addition of LiCl, x = 0.6, leads to a little more open network and consequently to a decrease of the boron coordination number. Total structure factors of the four glasses have been calculated and compared with the neutron scattering data of Borjesson, Torell and Howells (1989). The comparison is good at high q values, 5 angstrom-1 < q < 30 angstrom-1, and confirms the short-range structure of the B-O network found also in other experimental results. As for the low-q region of the structure factors, the results of simulation and neutron scattering agree less satisfactorily for the AgI-rich glass than for the LiCl-doped glass. This study confirms that the ordering of the medium-range structure decreases when LiCl salt is added to the pure binary matrix. The partial radial distribution functions as well as the total radial distribution function have also been calculated. This latter function compares quite well with the Fourier transform of the total structure factor for the AgI-rich glass obtained by neutron diffraction.