Thin Film Growth Effects on Electrical Conductivity in Entropy Stabilized Oxides

TL;DR

This study investigates how growth conditions affect the electrical conductivity of entropy-stabilized oxide thin films, revealing that lower temperature and pressure significantly enhance conductivity likely due to polaron hopping mechanisms.

Contribution

It provides the first detailed analysis of how substrate temperature and pressure influence the structure and electrical properties of entropy-stabilized oxide thin films.

Findings

Lower temperature and pressure increase electrical conductivity by ~40x.

Film texture and lattice parameters are strongly affected by growth conditions.

Conductivity likely arises from polaron hopping related to transition metal valence changes.

Abstract

Entropy stabilization has garnered significant attention as a new approach to designing novel materials. Much of the work in this area has focused on bulk ceramic processing, leaving entropy-stabilized thin films relatively underexplored. Following an extensive multi-variable investigation of polycrystalline (Mg$_{0.2}$Co$_{0.2}$Ni$_{0.2}$Cu$_{0.2}$Zn$_{0.2}$)O thin films deposited via pulsed laser deposition (PLD), it is shown here that substrate temperature and deposition pressure have strong and repeatable effects on film texture and lattice parameter. Further analysis shows that films deposited at lower temperatures and under lower oxygen chamber pressure are $\sim$40x more electrically conductive than otherwise identical films grown at higher temperature and pressure. This electronic conductivity is hypothesized to be the result of polaron hopping mediated by transition metal valence changes which compensate for oxygen off-stoichiometry.