The crystalline phase of (K2O)15(Nb2O5)15(TeO2)70 glass ceramic is a polymorph of K2Te4O9

Abstract We propose a new model for the crystalline phase of (K2O)15(Nb2O5)15 (TeO2)70 glass ceramic. A polymorph of K2Te4O9 in space group P21/c with a tetragonal lattice (a=7.821 A, b=16.590 A) is suggested which explains all the features of the observed diffraction patterns. This model of the ceramic phase has the cubic ordering of the cations that is indicated by the X-ray diffraction patterns, but has reasonable bond lengths and angles for the TeOx polyhedra and predicts the additional features that appear in the neutron diffraction data. The composition of the crystalline phase also explains the observed phase separation behavior. This new description of crystallization in the potassium niobate tellurite system has implications for understanding the non-linear optical response of the glass ceramic.