On (not) deriving the entropy of barocaloric phase transitions from crystallography and neutron spectroscopy

TL;DR

This paper reviews how disorder signatures in crystallography and neutron spectroscopy relate to entropy in materials, emphasizing the complexity of correlating structure, dynamics, and entropy, especially in barocalorics.

Contribution

It highlights the challenges in deriving entropy from experimental data and discusses the importance of combining multiple techniques for disordered crystalline materials.

Findings

Disorder signatures can arise from different types of disorder.

Correlating entropy with structure and dynamics is complex.

The approach is relevant beyond barocalorics to other caloric materials.

Abstract

We review well-known signatures of disorder in crystallographic and inelastic neutron scattering data. We show that these can arise from different types of disorder, corresponding to different values of the system entropy. Correlating the entropy of a material with its atomistic structure and dynamics is in general a difficult problem that requires correlating information between multiple experimental techniques including crystallography, spectroscopy, and calorimetry. These comments are illustrated with particular reference to barocalorics, but are relevant to a broad range of calorics and other disordered crystalline materials.