Synthesis and Characterization of Nanocrystalline RuO₂-ZrO₂

Abstract

The nanocrystalline samples of zirconium oxide doped with ruthenium oxide (RuO₂) have been synthesized from chlorides as precursors by chemical precipitation method. The as-prepared and annealed powder samples were studied by XRD, TEM and Impedance Spectroscopy. With 7.5 mol% of RuO₂, only a small percentage of ZrO₂ stabilizes in tetragonal form without stabilization in cubic form. With 9 mol% and above, ZrO₂ stabilizes in mixed phases having both tetragonal and cubic structure. On annealing, up to 1273 K the proportion of the cubic phase increases; however annealing at temperatures above 1273 K makes the sample to become monoclinic. Average grain size, as determined by Scherrer’s formula using X-ray linewidth, increases with increase of annealing temperature. The same trend is observed in TEM studies. TEM studies show the agglomeration of grains. X-ray diffraction for various concentrations of RuO₂ shows the presence of small amount of RuO₂ as impurity. This implies that Ru⁴⁺ goes to the interstitial position also in addition to its occupation of substitutional position of Zr⁴⁺ due to its smaller ionic radius (0.062 nm) compared to that of Zr⁴⁺ (0.084 nm). The impedance spectroscopy measurement shows that the conductivity decreases with an increase of grain size. The phase changes in the stabilization process with different concentrations and annealing temperatures, and growth of grain size in RuO₂ stabilized ZrO₂ will be presented. One of the salient points in this study is stabilization of ZrO₂ with RuO₂ alone without Y₂O₃ as reported in the literature.