Methods and means related to memory resistors are provided. A memristor includes at least two different active materials disposed between a pair of electrodes. The active materials are selected to exhibit respective and opposite changes in electrical resistance in response to changes in oxygen ion content. The active materials are subject to oxygen ion reconfiguration under the influence of an applied electric field. An electrical resistance of the memristor is thus adjustable by way of applied programming voltages and is non-volatile between programming events.