Flash luminescence, resistive switching and metal-insulator transitions in ceramic oxides

A combination of voltage-induced, reversible OFF-ON resistive switching and electroluminescence is reported in two materials that are both mixed conductors of oxide ions and electron holes. This occurs at high temperatures, 450-700 ˚C in cubic, fluorite-structured hafnia, YxHf1-xO2-x/2 and at more modest temperatures, 200-300 ˚C in Ca-doped BiFeO3 with a cubic perovskite structure. In both cases, a small voltage in the range 2-40 V is applied across mm-thick ceramic samples. Both effects are influenced greatly by oxygen exchange with the surrounding atmosphere and involve a combination of electron injection at the cathode, hole injection at the anode and generation of internal pn junctions. There are strong similarities between these effects and flash sintering but without the significant sintering, thermoluminescence and Joule heating that may be observed with flash sintering.