Optical implications of crystallite symmetry and structure in potassium niobate tellurite glass ceramics

We present combined results of optical, scattering, and spectroscopic studies of (K2O)(15)(Nb2O5)(15)(TeO2)(70) glass and glass ceramic and comment on possible mechanisms of the optical behavior in terms of existing theory. The glass ceramic is confirmed to generate second-harmonic light. Combined neutron and X-ray diffraction data have been indexed to an orthorhombic unit cell (a = 3.39 Angstrom, b = 4.78 Angstrom, c= 6.38 Angstrom). Additionally, we show that the previously proposed fluorite-based model is insufficient for the crystal phase using real-space analysis. The orthorhombic unit cell allows the possibility of a conventional explanation for the second-harmonic generation (SHG). Peak broadening and scattering length difference analyses are combined to formulate a model of anion disorder in the crystal phase. TEM and SAXS reveal domains of approximate to 15 nm in both the glass and glass ceramic. The role of liquid-liquid phase separation in the crystallization behavior of this material is discussed. Solid-state Nb-93 MAS NMR and Raman spectroscopy offer insight into Te valence and polyhedral distribution as well as Nb site symmetry and chemical connectivity. The effects of these geometries and anion disorder on optical response are discussed.