Copper - Copper Oxide Rectifiers

Figure 2. Characteristics of a crystal rectifier of the type shown in Fig. 1. For "volts positive" the polarities are as shown in the upper left; for "volts negative" they are reversed.

Various advanced theories have been presented² to explain the operation of the copper oxide rectifier, as it is commonly called. From a practical viewpoint it may be considered that the metallic copper contains many free electrons, and hence, when the oxide is made positive, electrons flow readily from the copper to the oxide.

Figure 3. Idealized characteristic curve and equivalent circuit of the crystal rectifier of Figs. 1 and 2. All such rectifiers do not have exactly the same characteristics.

When the polarity is reversed, negligible current flows because the oxide is a poor conductor and contains few free electrons.

Because the cuprous oxide is a poor conductor, a current-distributing electrode must be placed on it. In some rectifiers nickel is electroplated on the surface of the cuprous oxide. Copper oxide rectifiers are often called varistors, particularly in communication.