A new paradigm for modulated phases in multi-stage structural transformations

TL;DR

This paper introduces a comprehensive framework to understand multi-stage structural transformations, highlighting the role of modulated phases and anomalies in elastic and phonon properties across various materials.

Contribution

It provides a classification scheme for displacive transitions based on the presence of modulated phases and applies it to multiple material systems.

Findings

Identification of modulated phases as signatures of transition anomalies

Classification of transformations into four categories

Application to diverse materials including Ni-Mn-Ga and Cu-Zn-Al

Abstract

For multi-stage, displacive structural transitions we present a general framework that accounts for various intermediate modulated phases, elastic constant, phonon and related thermodynamic anomalies. Based on the presence or absence of modulated phases we classify these transformations in four categories and apply this approach to four different representative materials: Ni-Mn-Ga, NiTi(Fe),Ni-Al, Cu-Zn-Al and alpha-U. We suggest that the anomalous increase in elastic constant(s) and phonon frequency observed when approaching the martensitic transition from above is a signature of the conmensurate modulated phase.