Surface energetics of wurtzite and sphalerite polymorphs of zinc sulfide and implications for their formation in nature

TL;DR

This study investigates the surface energetics of zinc sulfide polymorphs, revealing how nanoscale effects influence their stability and occurrence in natural environments through combined experimental and thermodynamic modeling.

Contribution

It provides new experimental data and a thermodynamic model explaining the size-dependent stability of zinc sulfide polymorphs in nature.

Findings

Wurtzite has lower surface energy than sphalerite.

Wurtzite becomes stable below 10 nm particle size.

The model explains polymorph occurrence in diverse environments.

Abstract

Surface energetics of zinc sulfide nanoparticles determines their structure, properties, and occurrence. Using a combination of experimental techniques, we investigated the thermodynamics of the two polymorphs, sphalerite and wurtzite at bulk and nanoscale to understand their occurrence. Calorimetric measurements confirmed that wurtzite has a lower surface energy than sphalerite, which causes a reversal in phase stability at the nanoscale, with wurtzite energetically stable for particle size below 10 nm. Taking these surface energies into account, a simple model of the thermodynamics of the sphalerite - wurtzite transformation as a function of particle size and temperature can explain the occurrence of the zinc sulfide polymorphs in environments as diverse as ore bodies and planetary atmospheres.