Synthesis and characterization of nonconventional nickel-titania glasses by sol-gel route
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Synthesis and characterization of nonconventional nickel-titania glasses by sol-gel route T. K. Kundu and D. Chakravortya) Indian Association for the Cultivation of Science, Jadavpur, Calcutta 700 032, India (Received 27 May 1997; accepted 16 June 1998)
Glasses in the NiO–TiO2 system in the composition range 15 to 25 mol% of NiO have been synthesized by the sol-gel technique by heat treatment of the precursor sol at 500 ±C. The glass structure is built up by crosslinking of two units, namely TiO6 octahedron and NiO3 triangle. Glassy structure is confirmed at a microscopic level by scanning electron microscopy. An increase in the values of peak-to-peak width of electron paramagnetic resonance with increasing concentration of Ni21 is attributed to an enhanced interaction between neighboring paramagnetic Ni21 ions.
I. INTRODUCTION
In recent years, the sol-gel technique has been successfully used to prepare glasses which are difficult to synthesize by the melt quench method.1–3 In the former process molecular precursors are subjected to polymerization and polycondensation reactions leading to the formation of gels. Subsequent drying and densification transform the gels into glasses or ceramics depending on the composition of the starting chemicals.4 Glasses and gels containing transition metal and rare earth ions5–7 are of interest because of their technological applications involving optical and electrical memory switching. Several authors have reported on the preparation of colored films comprised of titanium dioxide and incorporating other ions like cesium,8 chromium,9 antimony,10 copper, and cobalt.11 They reported that the optical properties of the films were strongly modulated by the presence of transition metal ions. But in most of the cases, the anatase phase of titanium dioxide was precipitated at a temperature around 300 ±C. We have explored the possibility of inhibiting the growth of the anatase phase by introducing nickel oxide. A pure amorphous phase in the NiO–TiO2 system was obtained by this method within a critical range of composition by a suitable heat treatment. II. EXPERIMENTAL
Samples of compositions (100 2 x)TiO2 2 xNiO, where x 0–30 (mol%), were prepared by the solgel route. Starting materials were titanium alkoxide O4 (C12 H28 Ti) and nickel chloride (NiCl2 , 6H2 O) (supplied by Aldrich Chemicals, USA). A set of solutions were first prepared mixing ethyl alcohol and acetic acid in the volume ratio 75 : 25. Different mol% of O4 (C12 H28 Ti) a)
Also affiliated with Jawarharlal Nehru Centre for Advanced Scientific Research, Bangalore 560 064, India. J. Mater. Res., Vol. 14, No. 3, Mar 1999
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were added to the above solution in the volume ratio 1 : 8. The mixture was stirred for 2 h. Another solution was prepared by dissolving nickel chloride in distilled water. The latter was poured into the first and the resulting mixture was stirred for 2 h. The latter was kept in a polypropylene petri dish
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