SHORT-RANGE ORDER IN ULTRAPHOSPHATE GLASSES

The high real-space resolution of neutron diffraction experiments whic h is provided by use of spallation sources was exploited in order to d ifferentiate the unlike P-O bonds formed in the PO4 units of ultraphos phate glass networks. The two P-O peaks observed are assigned to oxyge n sites an bridging and terminal positions. The mean P-O distance is a lmost invariable versus composition. An elongation of both separate bo nds with increasing metal oxide content compensates for the enhanced f raction of the shorter bonds, i.e. those of the terminal oxygen atoms. The Ca-O coordination numbers of about 6 do not depend on composition .