The semiconducting properties of cuprous oxide

Abstract

A procedure has been developed for preparing reproducible specimens of cuprous oxide at the oxygen-poor limit of its composition range. The electrical conductivity and thermoelectric power of such specimens were measured simultaneously, and related to temperature within the range 20 to 1030° C. The conductivity-temperature curve consists of two limbs, the slopes of which correspond to activation energies of 0.300 and 1.04 eV respectively. The relation between thermoelectric power and temperature also falls into two segments, the temperature of discontinuity agreeing closely with the break in the conductivity curve. Below 355° C the thermo-electric power is quite independent of temperature and has a value 1.64 mV deg. -1 . Above 355° C the thermoelectric power decreases with rise in temperature; its sign does not change, but remains characteristic of a positive-hole conductor up to the highest temperatures investigated. The effect of oxygenating cuprous oxide of limiting composition has also been studied. With an ambient pressure of 9 mm oxygen the activation energies for conduction decreased to 0.238 and 0.877 eV respectively, and the constant value of the thermoelectric power dropped to 1.0 mV deg. -1 . The theoretical implications of these results are discussed, and it is concluded that the existing semi-conductor models provide no satisfactory explanation of a temperature-independent thermoelectric power in a region where the number of current carriers is strongly dependent on temperature.