Determination of the vibrational contribution to the entropy change at the martensitic transformation in Ni-Mn-Sn metamagnetic shape memory alloys: A combined approach of time-of-flight neutron spectroscopy and ab-initio calculations

TL;DR

This study quantifies the vibrational and electronic contributions to the entropy change during the martensitic transformation in Ni-Mn-Sn alloys using neutron spectroscopy and ab-initio calculations, aligning well with calorimetric data.

Contribution

It combines neutron scattering and ab-initio calculations to accurately determine vibrational entropy contributions in martensitic transformations.

Findings

Vibrational entropy contribution is approximately -36 J kg^(-1) K^(-1).

Total entropy change measured by calorimetry is about -41 J kg^(-1) K^(-1).

Electronic contribution accounts for the remaining entropy change.

Abstract

The different contributions to the entropy change linked to the austenite-martensitic transition in a Ni-Mn-Sn metamagnetic shape memory alloy have been determined by combining different experimental techniques. The vibrational contribution has been inferred from the vibrational density of states of both the martensitic and austenite phases. This has been accomplished by combining time-of-flight neutron scattering measurements and ab-initio calculations. Further, the electronic part of the entropy change has also been calculated. Since the martensitic transformation takes place between two paramagnetic phases, the magnetic contribution can be neglected and the entropy change can be reduced to the sum of two terms: vibrational and electronic. The obtained value of the vibrational contribution (-36 \pm 5 J kg^(-1) K^(-1)) nearly provides the total entropy change measured by calorimetry (-41 \pm 3 J kg^(-1) K^(-1)), the difference being the electronic contribution within the experimental error.