Local structure maturation in high entropy oxide (Mg,Co,Ni,Cu,Zn)1-x(Cr,Mn)xO thin films

TL;DR

This study investigates how local atomic structures in high entropy oxide thin films evolve with synthesis conditions, revealing phase transitions and atomic coordination changes driven by oxygen pressure.

Contribution

It provides new insights into the local structural evolution and phase behavior of high entropy oxides under different oxygen partial pressures.

Findings

Lattice parameter decreases with increasing oxygen pressure.

Cr, Co, Mn shift to favorable coordination with pressure.

Transition from rock salt to spinel structure observed.

Abstract

High entropy oxides (HEO)s have garnered much interest due to their available high degree of tunability. Here, we study the local structure of (MgNiCuCoZn)0.167(MnCr)0.083O, a composition based on the parent HEO (MgNiCuCoZn)0.2O.We synthesized a series of thin films via pulsed laser deposition at incremental oxygen partial pressures. X-ray diffraction shows lattice parameter to decrease with increased pO2 pressures until the onset of phase separation. X-ray absorption fine structure shows that specific atomic species in the composition dictate the global structure of the material as Cr, Co, and Mn shift to energetically favorable coordination with increasing pressure. Transmission electron microscopy analysis on a lower-pressure sample exhibits a rock salt structure, but the higher-pressure sample reveals reflections reminiscent of the spinel structure. In all, these findings give a more complete picture on how (MgNiCuCoZn)0.167(MnCr)0.083O forms with varying initial conditions and advances fundamental knowledge of cation behavior in high entropy oxides.