Formation of a metastable phase due to the presence of impurities

TL;DR

This paper investigates how impurities influence the formation of metastable phases during phase transitions, demonstrating that impurities can lower nucleation barriers and cause systems to follow Ostwald's rule, using Monte Carlo simulations of a Potts model.

Contribution

It reveals the role of impurities in promoting metastable phase formation and explains Ostwald's rule through a lattice model study.

Findings

Impurities reduce the barrier for heterogeneous nucleation of metastable phases.

The phase that forms depends on impurity presence and properties.

Impurities can cause systems to obey Ostwald's rule.

Abstract

Phase transitions into a new phase that is itself metastable are common; instead of the equilibrium phase nucleating a metastable phase does so. When this occurs the system is sometimes said to be obeying Ostwald's rule. We show how this can happen when there are impurities present that reduce the barrier to heterogeneous nucleation of the metastable phase. We do so by studying a Potts lattice model using Monte Carlo simulation. Thus, which phase forms depends not only on the properties of the different phases but also on the impurities present. Understanding why systems obey Ostwald's rule may therefore require a study of the impurities present.