Shapes of the noncentrosymmetric TeO5E groups in tellurite glasses with P2O5 additions

Abstract

Abstract The noncentrosymmetric shapes of the TeO n E units (n = 3, 4, and 5) are important for the nonlinear optical properties of the tellurite glasses (E – lone pair). An earlier diffraction work on the binary (TeO2)1−x (P2O5) x glasses reported Te−O coordination numbers larger than four, which means the rare case of proportions of TeO5E units. The distributions of the Te−O distances in these glasses differ from those known in the related crystal structures. The so far unknown shapes of the TeO5E units are determined by the use of a mechanical analog. Five steel balls can move freely in a spherical bowl. Under the effect of gravity, they take a structure that is equivalent to that of the five oxygen ligands of a TeO5E unit. The average bond lengths of the TeO5E groups obtained for the glasses differ a little from the lengths of this unit. The small differences are attributable to variations based on the uneven tensions caused by the network disorder. The mechanical analog was set up on basis of the present conceptions of the lone pair’s steric effects. The ratio of the ball’s and bowl’s diameters is taken from published analyses of crystal structures.