Room Temperature RF Sputtering of Mixed Ionic and Electronic Conductor Nd2Ni0.8Cu0.2O4+d films

TL;DR

This study demonstrates that room temperature RF sputtering with high power density can produce high-quality Nd2Ni0.8Cu0.2O4+δ thin films suitable for SOFC cathodes, simplifying fabrication of mixed ionic-electronic conductors.

Contribution

It introduces a scalable PVD method for fabricating Nd2Ni0.8Cu0.2O4+δ films at room temperature, optimizing sputtering parameters for phase purity and stoichiometry.

Findings

High power sputtering reduces spurious phases.

Films show resistivity similar to bulk materials.

Successful stabilization of the desired phase at room temperature.

Abstract

Lowering the operating temperature of Solid Oxide Fuel Cells (SOFCs) is essential for improving durability and enabling large scale commercialization. Mixed ionic-electronic conductors (MIECs) of the Ruddlesden-Popper family, such as Nd$2$Ni${1-x}$Cu$x$O${4+\delta}$ (NNCO), offer attractive cathode properties due to their high oxygen transport and favourable defect chemistry. In this work, we investigate the fabrication of Nd$2$Ni${0.8}$Cu${0.2}$O${4+\delta}$ thin films using a room temperature RF sputtering process followed by moderate temperature annealing. To simplify deposition, a single stoichiometric target was employed, despite the compositional challenges posed by elements with different sputtering yields. We examine the effect of sputtering power density on phase formation and film stoichiometry through X-ray diffraction, Rutherford Backscattering Spectrometry, Energy Dispersive X-ray Spectroscopy, and temperature dependent resistivity measurements. Increasing the sputtering power density strongly reduces the presence of spurious phases and promotes stabilization of the desired n=1 Ruddlesden-Popper phase. Films deposited at 230 W (3.1 W cm$^{-2}$) exhibit a predominant NNCO structure, elemental ratios close to nominal composition, and resistivity values consistent with bulk materials. These findings demonstrate that high power sputtering combined with ex situ annealing enables the production of NNCO thin films suitable for SOFC cathodes. The results support the potential of PVD based approaches for scalable fabrication of advanced SOFC components.