Relaxation of electronic defects in pure and dopedLa2O3observed by perturbed angular correlations

Abstract

Slow recovery processes of the electronic environment following the electron-capture decay of $^{111}\mathrm{In}$ can reduce the amplitude of the perturbed \ensuremath{\gamma}\ensuremath{\gamma}-angular correlation of a nuclear decay. This effect was used to quantitatively extract recovery rates of an electrically stable environment at the probe ion $^{111}\mathrm{Cd}$ in ${\mathrm{La}}_{2}$${\mathrm{O}}_{3}$. The recovery rates depend on the availability of electrons at the probe site, which in turn is governed by the concentration of electron sources and the transport mechanisms. Both properties are experimentally analyzed by variations of the temperature and oxygen partial pressure and by doping with two (Ba, Mg) and four-valent ions (Ce, Zr). Tunneling processes between defect levels in the band gap are proposed to account for the temperature dependence of the recovery rates. Unexpectedly, an enhanced electron availability is observed at temperatures below 200 K. The electric field gradients of substitutional $^{111}\mathrm{Cd}$ and those generated by intrinsic defects and dopants are analyzed. A comparison to the probe ion $^{111\mathit{m}}\mathrm{Cd}$, not affected by electron capture, is presented. \textcopyright{} 1996 The American Physical Society.