Microscopic nature of the metal to insulator phase transition induced through electroreduction in single-crystal KNbO3

Electroreduction of the crystalline perovskite KNbO₃ results in a change of the electrical resistivity by about 12-14 orders of magnitude from insulating to semimetallic at room temperature. This change is completely reversible through oxidation of the material. The semimetallic phase is characterized by a three-dimensional network of planar defects extending throughout the crystal. We have characterized the microscopic nature of this semimetallic phase by photoelectron spectroscopy after preparing the surface of the crystal to the same state. We also present evidence that at temperatures below 100 K these electroreduced materials may even become superconducting.