Structural Phase Transitions

TL;DR

This paper reviews the experimental studies of structural phase transitions, focusing on ferroelectrics, antiferroelectrics, incommensurate phases, and phenomena like soft modes, Kohn anomalies, and critical fluctuations, highlighting key discoveries and unresolved questions.

Contribution

It summarizes groundbreaking neutron scattering experiments on phase transitions and discusses the complex phenomena observed, emphasizing the interplay between experimental findings and theoretical challenges.

Findings

Soft mode behavior explains ferroelectric and antiferroelectric transitions.

Giant Kohn anomalies cause structural instabilities in one-dimensional metals.

Central peak and two-length scale phenomena are observed at phase transitions, with incomplete theoretical understanding.

Abstract

Gen Shirane began studying ferroelectrics while he was still based in Japan in the early 1950s. It was therefore natural that when he arrived at Brookhaven and began specialising in neutron scattering that he would devote much of his energy and expertise studying structural phase transitions. We review the ground breaking experiments that showed the behaviour of antiferroelectrics and ferroelectrics were reasonably described in terms of the soft mode concept of structural phase transitions. This work lead directly to Gen being awarded the Buckley prize and, jointly with John Axe, awarded the Warren prize. We then describe his work on incommensurate phase transitions and in particular how the giant Kohn anomalies are responsible for the structural instabilities in one-dimensional metals. Finally Gen carefully investigated the central peak and the two-length scale phenomena that occur at most if not all transitions. Due to Gens elegant experimental work we know a great deal about both of these effects but in neither case is theory able to explain all of his results