Pulsed neutron diffraction studies of RO.xB₂O₃ glasses: R=Ca, Sr and Ba; x=2, 3 and 4

Pulsed neutron diffraction experiments were performed on SrO.xB ₂O₃ (x=2, 3 and 4) and Na₂O.xB ₂O₃ (x=7/3, 4 and 9) glasses. With the help of molecular dynamics (MD) simulation using simple isotropic pair potentials, the cation dependence of the short range structure is discussed in order to investigate the role of metal oxides. Previous results for calcium and barium borate glasses have also been modified using improved analytical methods. For alkaline earth oxides, the fraction of B atoms coordinated by four nearest neighbour O atoms shows that the number of four coordinated B atoms in the alkaline earth borate glasses increases with increasing cation size, whereas that in alkali borate glasses decreases with increasing cation size. On the other hand, there are only small differences between sodium and alkaline earth borate glasses in the cation dependence of the other parameters such as the peak position and asymmetry of the BO correlation. Results from neutron diffraction experiments are in good agreement with those from MD calculations.