Chemical Stability of (Ag,Cu)2Se: a Historical Overview

Recent work on Cu2-x Se has caused strong interest in this material due to its high reported peak zT (1.5) and the reduction of thermal conductivity through the mechanism of liquid-like suppression of heat capacity. In the 1960s, 3M patented Cu1.97Ag0.03Se as "TPM-217." Over the following decade it was tested and developed by the 3M Corporation, at the National Aeronautics and Space Administration (NASA) Jet Propulsion Laboratory, Teledyne Energy Systems, and the General Atomics Corporation for use as a next-generation thermoelectric material. During these tests, extreme problems with material loss through Se vaporization and chemical reactions between the material and the device contacts were found. These problems were especially severe while operating under conditions of high As a result, the material system was abandoned. The results of these reports are discussed. A simple test of degradation of Cu2Se under conditions of applied current and thermal gradient was performed and showed results compatible with the work done by General Atomics.