METAL-SEMICONDUCTOR TRANSITION IN THE DEFECTIVE PEROVSKITE LACU1-XNIXO2.5+DELTA

Abrupt and reversible changes in the oxygen content and the electrical conductivity have been detected at similar to 500 degrees C in the an ion-deficient perovskite LaCu(1-x)Ni(x)O(2.5+)delta, which was synthet ized as part of this study. These changes accompany a transition from a metallic to a semiconducting behavior. The changes were found by x-r ay diffraction, differential thermal analysis, thermogravimetry, and m easurements of the electrical conductivity. The anomalies observed her e are shown to be accompanied by a structural phase transition and are linked with a sharp change in the Cu3+/Cu2+ cation ratio in the low- and high-temperature phases.