Ions In Tetrahedral Coordination Research Articles

Electron Paramagnetic Resonance of Copper in Beryllium Oxide

Paramagnetic-resonance absorption of copper-doped single crystals of beryllium oxide has been investigated at 9 GHz. The best-fit values to a spin Hamiltonian with $S=\frac{1}{2}$ are $|{g}_{\ensuremath{\parallel}}|=1.709\ifmmode\pm\else\textpm\fi{}0.002$, $|{g}_{\ensuremath{\perp}}|=2.379\ifmmode\pm\else\textpm\fi{}0.001$, $|{A}_{\ensuremath{\parallel}}|=(50\ifmmode\pm\else\textpm\fi{}1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{\ensuremath{-}1}$, $|{A}_{\ensuremath{\perp}}|=(108\ifmmode\pm\else\textpm\fi{}1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{\ensuremath{-}1}$, and $|Q|=(11\ifmmode\pm\else\textpm\fi{}1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{\ensuremath{-}1}$, where the hyperfine values refer to the ${\mathrm{Cu}}^{63}$ isotope, for which $I=\frac{3}{2}$. The observations are interpreted as due to ${\mathrm{Cu}}^{2+}$ substitutional for beryllium at normal lattice sites. Crystal-field theory which incorporates covalent bonding has been used to interpret these results in terms of the $3{d}^{9}$ configuration of ${\mathrm{Cu}}^{2+}$ in ${C}_{3v}$ symmetry. The experimental results are shown to be consistent with the theory, which yields an orbital reduction factor of 0.6, and values for $〈{r}^{\ensuremath{-}3}〉$ and the contact hyperfine interaction close to those for the free ion. The results are also compared with some other cases of $3{d}^{9}$ ions in tetrahedral coordination.