ComplexGa0(4p1)andIn0(5p1)centers in KC1. Electron-spin-resonance study

A detailed electron-spin-resonance (ESR) study has been made of trapped electron centers in KC1 doped with the $n{s}^2$ metal ions $M^{+}={\mathrm{Ga}}^{+},{\mathrm{In}}^{+}$. X-ray irradiation at 77 K produces by simple electron trapping the primary $M^0$ atom defects which manifest themselves as linear symmetric $〈100〉$-oriented M${\mathrm{Cl}}_2^{2-}$ molecule ions. Both centers exhibit a reorientation motion with very low activation energy, and the relevance of this for the nonobservability of the primary T$1^0$ ESR spectrum is discussed. An x-ray irradiation above 220 K, where negative ion vacancies become mobile, leads to several complex $M^0$ defects. Two of them, called $M^0\mathrm{}\left(1\right)\mathrm{}$ and $M^0\mathrm{}\left(2\right)\mathrm{}$, are analogous to the T$1^0$(1) and T$1^0$(2) defects studied earlier, and their structures are confirmed: In $M^0\mathrm{}\left(1\right)\mathrm{}$ a $M^0$ on a cation site is associated with a single anion vacancy, and in $M^0\mathrm{}\left(2\right)\mathrm{}$ the $M^0$ is flanked by two anion vacancies. For both centers there is an appreciable delocalization of the unpaired electron. An additional center, called ${\mathrm{Ga}}^0$ (axial), is shown to be in essence an orthorhombic center which exhibits even at ∼10 K a rapid reorientation between two equivalent Jahn-Teller distortions in a {100} plane. An analysis of the ESR parameters reveals regularities in the variation of the isotropic part of the $M^0$ hyperfine interaction which can be related to the even or odd character of the perturbing crystal field. Extensive data on the production and thermal properties of the different defects are also given.