Hyperfine and superhyperfine interactions forMo5+in SnO2

The ESR spectra of polycrystalline samples of Mo-doped Sn${\mathrm{O}}_2$ have been studied at the $X$ and $Q$ bands at temperatures of 77 and 300 K. Comparison is made with previously reported studies of interstitial and substitutional ${\mathrm{}\left(\mathrm{nd}\right)\mathrm{}}^1$ ions in rutile-type single crystals. The observed spectra are attributed to a ${\mathrm{Mo}}^{5+}$ ${\mathrm{}\left(4d\right)\mathrm{}}^1$ ion in a substitutional cation site. With the choice of axes $\overrightarrow{\mathrm{x}}\parallel \left[\overline{1}10\right]$, $\overrightarrow{\mathrm{y}}\parallel \mathrm{}\left[001\right]\mathrm{}$, and $\overrightarrow{\mathrm{z}}\parallel \mathrm{}\left[110\right]\mathrm{}$, the spin-Hamiltonian parameters are $g_{\mathrm{xx}}=1.891\mathrm{}$, $g_{\mathrm{yy}}=1.835\mathrm{}$, $g_{\mathrm{zz}}=1.923\mathrm{}$; $A_{\mathrm{xx}}=21.3\mathrm{}\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $A_{\mathrm{yy}}=26.5\mathrm{}\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $A_{\mathrm{zz}}=62\mathrm{}\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$; $a_{\mathrm{xx}}=248\mathrm{}\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $a_{\mathrm{yy}}=273\mathrm{}\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $a_{\mathrm{zz}}=250\mathrm{}\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$; $b_{\mathrm{xx}}=51.5\mathrm{}\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $b_{\mathrm{yy}}=42.5\mathrm{}\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $b_{\mathrm{zz}}=42\mathrm{}\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$. The last two tensors correspond to superhyperfine interactions with two sets of Sn nuclei located respectively on the $y$ axis and in the $\mathrm{xy}$ plane. The $g$ tensor is computed by using the parametrized-crystal-field theory; hyperfine and superhyperfine interactions are interpreted on the basis of a molecular-orbital treatment of the unpaired electron, and the delocalization of this electron is discussed.