APPEARANCE OF TWO-PHASE MIXTURE OF QUASICRYSTAL AND APPROXIMANT - FREE ENERGY ANALYSIS AND EXPERIMENT —

摘要

We have constructed a free energy formula, in which the alloy composition to-gether with the phason strain is explicitly included as an order parameter. The free energy is expressed by the sum of three terms determined by phason elastic strain E, composition c and the coupling between E and c. The equilibrium state of the system has been obtained by analyzing the potential surface of the two-dimensional (E,c) space at each temperature. The first order phase transition accompanied by a two-phase mixture of quasicrystal and approximant is predicted. An intermediate state between the icosahedral phase and the 2/1 approximant observed in Al-Cu-Fe system is considered to be the two-phase mixture caused by phason fluctuation from one-dimensional and two-dimensional analyses of HREM image. The result is discussed in terms of the present free energy analysis.