Paramagnetic Resonance of Ni2+ and Ni3+ in TiO2

Abstract

Electron spin resonance was observed in nickel-doped rutile. The majority of the nickel is in the divalent state, and probably occupies an interstitial position. The parameters describing the ${\mathrm{Ni}}^{2+}$ spectra are: $S=1\mathrm{}$; $g\left[z\right]=2.20\mathrm{}$; $g\left[y\right]=g\left[x\right]=2.10\mathrm{}$; $D=-8.3\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$; and $\mathrm{}\left|E\right|=0.137\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$ at 4.2°K. Some of the nickel, also probably occupying an interstitial position, is in the trivalent state, as was verified by oxidation-reduction tests. The parameters are: $S=\frac{1}{2}$ and $g\left[z\right]=2.254\mathrm{}$; $g\left[c\right]=2.085\mathrm{}$; $g\left[x\right]=2.084\mathrm{}$. A third spectrum due to nickel in an unknown valence state appears after the sample is illuminated. It represents nickel in a substitutional site with $S=\frac{1}{2}$ and $g\left[110\right]=2.272\mathrm{}$; $g\left[c\right]=2.237\mathrm{}$; $g\left[1\mathrm{}\overline{1}0\right]=2.050$.