Localized Metallic Conductivity and Self-Healing during Thermal Reduction of ${\mathrm{SrTiO}}_3$

The occurrence of metallic conductivity in ${\mathrm{SrTiO}}_3$ single crystals is reported for reduction under low partial pressure of oxygen at $800°\mathrm{C}$. This transition is shown to result from the formation of a high concentration of vacancy defects along a network of extended defects within the skin region. A self-healing phenomenon is observed for progressive reduction which causes the concentration of initially introduced defects to decrease in the course of heat treatment and leads to a breakdown of the metallic conductivity as well as a substantial loss of optical subgap absorption.