Rupp J L M, Fabbri E, Marrocchelli D, et al. Scalable oxygen‐ion transport kinetics in metal‐oxide films: impact of thermally induced lattice compaction in acceptor doped ceria films[J]. Advanced Functional Materials, 2014, 24(11): 1562-1574.
ABSTRACT
In this paper, we focus on the effect of processing-dependent lattice strain on oxygen ion conductivity in ceria based solid electrolyte thin fi lms. This is of importance for technological applications, such as micro-SOFCs, microbat-teries, and resistive RAM memories. The oxygen ion conductivity can be signifi -cantly modifi ed by control of lattice strain, to an extent comparable to the effect of doping bulk ceria with cations of different diameters. The interplay of dopant radii, lattice strain, microstrain, anion-cation near order and oxygen ion trans-port is analyzed experimentally and interpreted with computational results. Key fi ndings include that fi lms annealed at 600 ° C exhibit lattice parameters close to those of their bulk counterparts. With increasing anneal temperature, however, the fi lms exhibited substantial compaction with lattice parameters decreasing by as much as nearly 2% (viz, Δ d 600–1100 ° C : –1.7% (Sc +3 ) > –1.5% (Gd +3 ) > –1.2% (La +3 )) for the annealing temperature range of 600–1100 ° C. Remarkably 2/3 rd of the lattice parameter change obtained in bulk ceria upon changing the acceptor diameter from the smaller Sc to larger La, can be repro-duced by post annealing a fi lm with fi xed dopant diameter. While the impact of lattice compaction on defect association/ordering cannot be entirely excluded, DFT computation revealed that the main effect appears to result in an increase in migration energy and consequent drop in ionic conductivity. As a conse-quence, it is clear that annealing procedures should be held to a minimum to maintain the optimum level of oxygen ion conductivity for energy-related appli-cations. Results reveal also the importance to understand the role of electro-chemo-mechanical coupling that is active in thin fi lm materials.
