Martensitic transformation B2–R in Ni–Ti–Fe: experimental determination of the Landaupotential and quantum saturation of the order parameter

Abstract

The Landau potential of the martensitic phase transformation inNi46.8Ti50Fe3.2 was determined using high resolution x-ray diffraction to measure the spontaneous strainand calorimetric measurements to determine the excess specific heat of the R phase. Thespontaneous strain is proportional to the square of the order parameter which is tested bythe relation of the excess entropy and the order parameter. The parameters ofthe Landau free energy were determined by fitting the temperature evolution ofthe order parameter and using the scaling between the excess entropy and theorder parameter. The double well potential at absolute zero temperature wascalculated and the interface energy and domain wall thickness were estimated.