Perturbed-angular-correlation measurements were carried out after implantation of ${}_{}{}^{111}{}_{}{}^{}\mathrm{In}$ into amorphous and polycrystalline powder samples of α- and β-${\mathrm{Ga}}_2$${\mathrm{O}}_3$, and single crystals of β-${\mathrm{Ga}}_2$${\mathrm{O}}_3$. After annealing of the radiation damage the quadrupole hyperfine interactions of ${}_{}{}^{111}{}_{}{}^{}\mathrm{Cd}$ were determined. In both α- and β-crystallne phases, three electric-quadrupole interactions were observed. In addition, the orientations of the electric-field gradients in β-${\mathrm{Ga}}_2$${\mathrm{O}}_3$ at the probe sites were determined. In β-${\mathrm{Ga}}_2$${\mathrm{O}}_3$ preferential substitutional In occupation of the octahedral sites was found. Two of the quadrupole interactions in α- and β-${\mathrm{Ga}}_2$${\mathrm{O}}_3$ are attributed to different charge states of the ${}_{}{}^{111}{}_{}{}^{}\mathrm{Cd}$ impurity (${\mathrm{Cd}}^0$) and (${\mathrm{Cd}}^{\mathrm{-}}$). Their populations varied in a reversible way in the temperature range 450–700 K and also can be influenced by the oxygen pressure.

• Received 26 March 1993

DOI:https://doi.org/10.1103/PhysRevB.48.10052