Driving force for martensitic transformation in Ni$_{2}$Mn$_{1+x}$Sn$_{1-x}$

TL;DR

This study uses ab-initio calculations to identify the microscopic driving force behind martensitic transformation in Ni$_{2}$Mn$_{1+x}$Sn$_{1-x}$ alloys, highlighting increased Ni-Mn hybridization and atomic movements as key factors.

Contribution

It provides a detailed microscopic explanation for the martensitic transition, emphasizing the role of Ni-Mn hybridization and atomic forces, with quantitative analysis showing minimal impact of band Jahn Teller effects.

Findings

Martensitic transition occurs beyond x=0.36 in Ni$_{2}$Mn$_{1+x}$Sn$_{1-x}$ alloys.

Increased Ni-Mn hybridization drives the transformation.

Band Jahn Teller effects have a minor role in this transition.

Abstract

The martensitic transformation in Ni$_{2}$Mn$_{1+x}$Sn$_{1-x}$ alloys has been investigated within ab-initio density functional theory. The experimental trend of a martensitic transition happening beyond $x$ = 0.36 is captured within these calculations. The microscopic considerations leading to this are traced to increased Ni-Mn hybridization which results from the Ni atom experiencing a resultant force along a lattice parameter and moving towards the Mn atoms above a critical concentration. The presence of the lone pair electrons on Sn forces the movement of Ni atoms away from Sn. While band Jahn Teller effects have been associated with this transition, we show quantitatively that atleast in this class of compounds they have a minor role.