Negative bulk modulus and possibility of loss of elastic stability near tricritical transitions in thin films on substrates

TL;DR

This paper investigates elastic anomalies in thin films near phase transitions, revealing conditions under which the bulk modulus becomes negative, indicating potential loss of elastic stability and the importance of inhomogeneous states.

Contribution

It introduces a Landau-like approach to analyze elastic moduli anomalies and demonstrates the possibility of negative bulk modulus near tricritical transitions in thin films.

Findings

Negative bulk modulus can occur near phase transitions.

Homogeneous low-symmetry states may become unstable.

Elastic stability loss is linked to sign change of bulk modulus.

Abstract

Within the Landau-like approach we study anomalies of elastic moduli at phase transitions in thin films on substrates. We consider the case where, similar to many experimental cases, the first-order transition in free crystal would convert into a second order in the film if the system remained homogeneous. It is shown, however, that apart from its questionable thermodynamic profitability, the homogeneous state of low-symmetry phase may become absolutely unstable which is signaled by changing of sign of its bulk modulus.