A small fraction of defects can order a crystal

Abstract

Based on calculations of the activation process parameters (vacancy formation and self-diffusion) for gold at the temperature range T = 10–1330 K, the correlations of the activation process parameters si(T) ∼ hi(T) and si(T) ∼ vi(T), along two isobars. P = 0 and 24 GPa, are studied. Here hi is the enthalpy, si is the entropy, and vi is the volume of the activation process, i.e. for the formation of an electroneutral vacancy (i = v) or for the self-diffusion of atoms (i = d). It is shown that if, during isobaric heating, an energy less than a certain value (hi < hsi) is required to create a defect (vacancy or diffusing atom), or if the resulting defect has a volume less than a certain value (vi < vsi), then this defect has a negative entropy, i.e. this defect orders the crystal. However, if a larger energy value is required to create a defect (hi > hsi) or this defect has a noticeable volume (vi > vsi), then this defect has a positive entropy, i.e. this defect disorders the crystal. It is shown that at a low concentration of defects, they order the crystal, and only starting from a certain concentration (Xsi) does the defect formation entropy pass into the positive region, where defects disorder the crystal. The changes in the functions of hsi, vsi, and Xsi with increasing pressure are studied.