Influence of NiO on phase transformations and optical properties of ZnO–Al2O3–SiO2 glass-ceramics nucleated by TiO2 and ZrO2. Part I. Influence of NiO on phase transformations of ZnO–Al2O3–SiO2 glass-ceramics nucleated by TiO2 and ZrO2

• Zinc-aluminosilicate glass-ceramics based on Ni,Ti-doped gahnite nanosized crystals
• Inhomogeneity of parent glasses according to SAXS and Raman spectroscopy
• Metastable nickel titanate-zirconate nanophase with fluorite-type structure
• Sequence of phase transformations in glasses doped with low and high concentrations of NiO

The influence of NiO addition (from 0.1 up to 3 mol%) on structure and phase transformations of zinc aluminosilicate glasses nucleated by a mixture of TiO2 and ZrO2 has been studied using small angle X-ray scattering (SAXS), X-ray diffraction (XRD) analysis, Raman scattering and optical absorption spectroscopy. All parent glasses were X-ray amorphous and according to SAXS data inhomogeneous. Though SAXS intensity increased with increasing the NiO content in parent glasses, the distance between the inhomogeneous regions was independent of the NiO content implying that NiO does not play a role of additional nucleating agent. The processes of phase transformations were different for glasses doped with 0–0.1 and 1–3 mol% NiO. In glasses containing 0–0.1 mol% NiO, ZrTiO4 and Ni,Ti-doped gahnite crystals precipitated simultaneously starting from heat-treatment at above 730 °C; traces of ZrO2 tetragonal crystals were found in glass-ceramics prepared at 1000–1200 °C. In glasses doped with 1–3 mol% NiO, metastable nickel titanate-zirconate crystals with fluorite-type structure and size of 4–5 nm appeared during heat-treatments in the temperature range of 730–800 °C, the fraction of this phase increased with the increase of the NiO content in the parent glass. Nickel titanate-zirconate crystals with fluorite structure decomposed during annealing at above 800 °C. Ni,Ti-doped gahnite crystals precipitated starting from heat-treatment at 800 °C; ZrO2 tetragonal crystals were formed at 900–1200 °C.