Structure of tellurite glasses—effects of K2O or P2O5additions studied by diffraction

Neutron and x-ray diffraction experiments of high resolving power with neutrons from a spallation source and high-energy photons from a synchrotron have been performed on compositional series of binary tellurite glasses with additions of K 2 O or P 2 O 5 (max. 16 or 32 mol%). Since the P–O bond lengths do not interfere with the Te–O peaks the Te–O and O–O correlations are approximated by Gaussian fitting of the x-ray and neutron correlation functions up to lengths of 0.28 nm. In the case of K 2 O–TeO 2 glasses reasonable assumptions are made for the K–O first-neighbour peaks. Te–O and O–O coordination numbers are four and five for the glasses of compositions close to pure TeO 2 which indicates formation of a three-dimensional network of corner-connected TeO 4 trigonal bipyramids. The tellurite network groups are TeO 4 and TeO 3 units in K 2 O–TeO 2 glasses and TeO 4 and TeO 5 units in P 2 O 5 –TeO 2 glasses. Additional Te–O neighbours found at 0.23 nm< r <0.26 nm for K 2 O–TeO 2 glasses suggest the existence of TeO 3+1 units and those found at 0.23 nm< r <0.29 nm for the P 2 O 5 –TeO 2 glasses indicate the existence of distorted TeO 6 polyhedra. Tellurite networks are flexible to form the appropriate coordination environments for quite different ions or groups of opposite charge such as K + ions and (PO 4/2 ) − tetrahedra where change of the TeO n network units provides the needed number of oxygen neighbours.