Quantitative Landau potentials for the martensitic transformation in Ni-Al

The martensitic phase transformation in Ni-Al (63.5 at. % Ni) is described by a Landau-type Gibbs free energy G(Q)=1/2A Theta(s)(coth(Theta(s)/T)-coth(Theta(s)/T-C))Q(2)+1/4BQ(4)+1/6CQ(6), with A=5.6 J K-1 mol(-1), B=-3493 J mol(-1), C=4901 J mol(-1), T-C=86 K, and Theta(s)=257 K. The dispersion (Ginzburg) energy was estimated to be g=60 J mol(-1) nm(2). This potential was determined from high resolution diffraction data to determine the spontaneous strain as proxy for the order parameter Q and differential scanning calorimetry measurements for the calibration of the excess entropy of the martensitic phase transformation. The Gibbs free energy is compared with equivalent functions of Ni-Ti, quartz, KMnF3, BaTiO3, and SrTiO3. (C) 2007 American Institute of Physics.