Structure of M2O-B2O3 (M : Na and K) glasses and melts by neutron diffraction

The structures of alkali berate glasses, M2O-B2O3, and melts with 10 and 30 mol% M2O (M = Na and K) have been studied by pulsed-neutron total scatteri ng measurements, With an increase of M2O content, the first peak of the exp erimental radial distribution function corresponding to the nearest neighbo r B-O correlation spreads asymmetrically to the higher-r side, and the coor dination number of O atoms around a reference B atom, NB-O, increases from 3.0 to 3.4 similar to 3.5, reflecting a structural change from BO3 triangle units to BO4 tetrahedral units. It can be concluded from the neutron resul ts that some of the BO3 units present are converted to BO4 units during the addition of up to 30 mol% M2O to the B2O3 and that they melt in a way simi lar to M2O-B2O3 glasses. XAFS studies in potassium berate glasses have made important contributions to our understanding of the network-modifying stru cture of glass. The local structure in K2O-B2O3 glasses has been determined in order to elucidate the environment of the network modifying K+ ions. Th e average coordination number, NK-O, Of oxygen around K+ cations and the me an distance, r(K-O), are found to be approximately 6 and 2.83-2.86 Angstrom , respectively. (C) 1999 Elsevier Science Ltd. All rights reserved.