The physics of the boson peak in Cu-based shape-memory alloys

We report specific heat measurements from 2 to 300 K in two CuZnAl shape-memory alloys. One remains in the parent phase, while the other is in the martensitic phase over the full measurement range. Data confirm the existence of a boson peak in the parent L 2 1 -phase of the studied material. A model is proposed that assumes that the boson peak is associated with the excess of vibrational entropy of the L 2 1 -phase with respect to the martensitic phase. The computed excess of entropy is in agreement with data obtained from calorimetric measurements in CuZnAl samples of selected compositions that transform martensitically in the temperature range from 30 to 250 K.