Structural studies of K_2O-B_2O_3 melts and glasses

摘要

The structures of alkali borate glasses and melts with 10 and 30 mol percent M_2O (M=Na and K) have been studied by pulsed neutron total scattering measurements. With an increase of M_2O content, the first peak of the experimental radial distribution function, corresponding to the nearest neighbour B-O correlation spreads asymmetrically to the higher-r side and the coordination number of O atoms around a reference B atom, N_(B-O), increases from 3.0 to 3.4 approx 3.5 reflecting a structural change from BO_3 triangle units to BO_4 tetrahedral units. It can be concluded from the neutron results that some BO_3 units present are converted to BO_4 units on the addition of up to 30 mol percent M_2O to the B_2O_3 melt in the same way as in M_2O- B_2O_3 glasses. XAFS studies of potassium borate glasses have made an important contribution to our understanding of the network modifying structure of glass. The local structure in K_2O-B_2O_3 glasses has been determined in order to make clear the environment of the network modifying K~(+) ions. The average coordination number, N_(K-O), of oxygen around K~(+) cations and the mean distance, r~(K-O), are found to be approximately 6 and 2.83 approx 2.86 A, respectively.