Search for a novel zero thermal expansion material: dilatometry of the AgI-CuI system

AgI is a well-known superionic conductor possessing a negative thermal expansion (NTE) coefficient while CuI is a p-type semiconductor possessing a positive thermal expansion coefficient. Pellets of X-Ray Diffraction (XRD) characterized compositions in the AgI-CuI system namely, beta AgI, gamma AgI, Ag0.5Cu0.5I, Ag0.25Cu0.75I, Ag0.10Cu0.90I, Ag0.05Cu0.95I and gamma CuI have been examined by quartz pushrod dilatometry measurements in order to look for a zero thermal expansion material. It is found that the systematic displacement of Ag by Cu gradually reduces the NTE anomaly in AgI. The composition Ag0.25Cu0.75I apparently exhibits near-zero thermal expansion. The results are discussed qualitatively in terms of relevant models