579. Solid transitions in mixed crystals of ethylene dichloride and ethylene dibromide

Abstract

INTRODUCTION In principle, the heat capacity curve of a solid substance can give information about the dependence of energy absorption on temperature of the crystal lattice, and hence on the mechanism of any phase changes which occur therein. In practice, however, the amount of information is limited (a) by the fact that a considerable contribution to the measured Cp comes from the term f32VTja; (b) by the lack of an adequate theory of the heat capacities of complex crystals. In certain cases, though, considerable insight can be obtained by diluting the lattice of a compound which undergoes a phase transition with a second kind of molecule or ion, and observing the effect on the nature and magnitude of the transition. The added component has usually been one which itself has no transitions', but a few studies have been made of mixed crystals both of whose components exhibit solid transitions2, when the phenomena are naturally more complex. This paper concerns heat capacity measurements on mixtures of ethylene dichloride and dibromide, both of which undergo solid transitions, and form a continuous series of mixed crystals.