TABLE OF CONTENTS Let us now consider several aspects of the concepts discussed above. From the cohesive energy values listed in data banks for non-transition elements it is possible to deduce that usually the fcc structure (the ideally close-packed structure) is more stable than the bcc structure (a less close-packed structure). [*] (In this context, the term packing is meant to correspond to nearest-neighbor coordination number rather than atomic volume. The lower this coordination number the more open is the packing in the present usage.) Then, equation 1.3 yields that the entropy of thermal origin for these elements is higher for the bcc crystal structure relative to that for the fcc structure. This result is illustrated in Figure 1.2a. As shown there, the energy and entropy of each phase has been assumed to be independent of temperature (i.e. the entropy equals ?[ ?G/ ?T] P and hence a constant entropy corresponds to a constant slope of the line representing the dependence of the free energy G on temperature T). In general, this assumption is not representative of the real behavior. The entropy of a phase increases with increasing temperature and the dependence of free energy on temperature corresponds more to that shown in Figure 1.2(b). The specific heat is proportional to the curvature of the G(T) line, i.e.
Since, the specific heat of materials has positive definite values, then the curvature of the G(T) line must be...
