Comments on the Pressure Variation of the Gibbs Energy for Bound and Unbound Defects

The pressure derivative v of the Gibbs energy g for “unbound” and “bound” defects (i.e. vacancies or interstitials attracted by aliovalent impurities) is studied. It is shown that for the formation and migration of defects the ratio v/g depends solely on well‐known macroscopic properties; applications are presented for self‐diffusion in f.c.c. and b.c.c. metals and for ionic conductivity of silver halides. In the case of ionic solids containing “bound” defects, a gradual variation of pressure results in the appearance of a transient polarization or depolarization current that maximizes at a certain pressure P cr . The way of analysing this piezo‐stimulated current (PSC) spectrum is discussed. The fact that the value of P cr does not have to coincide with the pressure at which fracture occurs provides a useful tool for applying PSC to geophysics.