High Entropy Alloy CrFeNiCoCu sputtered films

TL;DR

This study reports the synthesis, structural characterization, and electrical properties of sputtered CrFeNiCoCu high entropy alloy films, revealing their stable fcc structure, metallic resistivity, and complex electronic behavior influenced by annealing conditions.

Contribution

It provides detailed insights into the microstructure, electronic properties, and stability of CrFeNiCoCu HEA films, including effects of annealing atmospheres on their surface and phase stability.

Findings

HEA films exhibit a stable fcc solid solution with columnar grains.

Electrical resistivity is around 140 μΩcm with a metal-like temperature dependence.

Annealing in oxygen causes surface oxidation and phase demixing.

Abstract

High entropy alloy(HEA) films of CrFeCoNiCu were prepared by sputtering, their structure was characterized, and their electric properties measured by temperature dependent Hall and Seebeck measurement. The HEA films show a solid solution with fcc structure, and a 111 texture with columnar grains of widths 15-30 nm extending through film thickness with very many twins. The residual electrical resistivity of the films is around 140 {\mu}{\Omega}cm and the temperature dependence of the resistivity is metal-like. The temperature coefficient of resistivity (TCR) is small (2 ppm/K). The Hall coefficient is positive while the Seebeck coefficients is negative. This is interpreted as arising from an electronic structure where the Fermi level passes through band states having both holes and electrons as indicated by band structure calculations. The HEA structure appears stable for annealing in vacuum, while annealing in an oxygen containing atmosphere causes the surface to oxidize and grow a Cr-rich oxide on the surface. This is then accompanied by demixing of the HEA solid solution and a decrease in residual resistance of the film.