8. First order crystal transformation. Consider a crystal that can exist in either of two structures, denoted by at and (i. We suppose that the or structure is the stable low temperature form and the [3 structure is the stable high temperature form of the substance. If the zero of the energy scale is taken as the state of separated atoms at innity, then the energy density U(0) at r = 0 will be negative. The phase stable at r = 0 will have the lower value of UtO); thus U,(O)