Solid-solid volume collapse transitions are zeroth order

TL;DR

This paper introduces an exactly solvable elastic model for volume collapse transitions in solids, revealing a zeroth order transition with intrinsic hysteresis and critical behavior, relevant to materials like Ce and SmS.

Contribution

The authors develop a non-linear elastic model that predicts a zeroth order volume collapse transition with unique thermodynamic properties and critical phenomena.

Findings

Transition is forbidden within a pressure window, causing hysteresis.

Transition exhibits a discontinuity in thermodynamic potential, characteristic of zeroth order.

Critical point exists where the transition window closes at a specific temperature.

Abstract

We present an exactly solvable non-linear elastic model of a volume collapse transition in an isotropic solid. Integrity of the lattice through the transition leads to an infinite-range density-density interaction, which drives classical critical behavior. Nucleation is forbidden within a pressure window leading to intrinsic hysteresis and an unavoidable discontinuity of the thermodynamic potential (zeroth order transition). The window shrinks with increasing temperature ending at a critical point at a temperature related to the shear modulus. Mixed phases behave non-extensively and show negative compressibility. We discuss the implications for Ce, SmS, and related systems.