Unusual phase formation in reactively sputtered La-Co-O perovskite thin films

TL;DR

This study reports an unusual self-organized phase formation in La-Co-O perovskite thin films during reactive sputtering, revealing a new growth mechanism influenced by oxygen flux and temperature, useful for exploring complex perovskite libraries.

Contribution

It uncovers a novel self-organized growth phenomenon in La-based perovskite films during reactive sputtering, dependent on process parameters, and suggests a CVD-like growth mechanism.

Findings

Formation of homogeneous single-phase regions instead of composition gradients.

Dependence of phase formation on O2-flux and substrate temperature.

Potential for systematic exploration of multinary perovskite libraries.

Abstract

La-based perovskites are a versatile class of materials that are of interest for solid oxide fuel cells and electrocatalytic water splitting. During fabrication of composition spread materials libraries of La-Co-based oxide systems for the discovery of new catalytic materials, an unusual phase formation phenomenon was observed: instead of the expected continuous composition gradient, regions with homogeneous composition and single-phase structure (La2O3 or stoichiometric La-perovskite) form. This phenomenon occurs during reactive co-sputtering and is dependent on O2-flux and substrate temperature, investigated from room temperature up to 700 C and is independent of the used substrate. It can be described as a self-organized growth, where excess transition metal cannot be incorporated into the growing film and the forming single-phase regions. It is hypothesized that due to the high reactivity of La and the significantly low formation energies of La2O3 and La-perovskites, the reactive sputter deposition of La-based oxide films can turn, regarding film growth, into a partial CVD-like process which results in the unusual self-organized growth of single-phase regions. This phenomenon can be leveraged for the exploration of multinary perovskite thin film libraries, where the B-site atoms of La-perovskites are systematically substituted.