Deposition, Structure, and Properties of Cermet Thin Films Composed of Ag and Y‐Stabilized Zirconia

Abstract

Ag1-=[(Y20~)0.1(ZrO2)0.9]= (YSZ) cermet thin films have been deposited by reactive magnetron cosputtering from Ag and Zr/Y targets in Ar-O2 mixtures. The deposition conditions were such that the YSZ component in the films was fully oxidized. The film densities varied from =75% to >85% as the total pressure was decreased from 20 to 5 mTorr. Film resistivities p varied with Ag volume fraction fag from 5 • 10 -6 ~3-cm to >109 ~-cm. For fag < 0.4, p decreased rapidly with increasing fag. For fag > 0.4, p decreased more gradually with increasing fag. P in annealed films ranged from 4 • 10 -4 f~-cm for fag = 0.4 to 5 • 10 -6 ~-cm for pure Ag. Long term (>100 h) annealing at -> 700~ resulted in a gradual increase in cermet resistivity due to Ag evaporation and Ag segregation to surface islands. Both decomposition mechanisms were effectively suppressed at up to 750~ by depositing a 1 ~m thick porous perovskite cap layer on the cermet. Complex impedance spectroscopy measurements in air of cermet electrodes on YSZ electrolytes gave interfacial resistances that were a factor of =6 lower than those of pure Ag electrodes, e.g., 1.4 ~-cm 2 at 750~ Ag-YSZ cermets thus have potential as high-conductivity, low-overpotential air electrode materials for solid-oxide electrochemical devices operating at temperatures _<750~ ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 138.251.14.35 Downloaded on 2015-05-16 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 138.251.14.35 Downloaded on 2015-05-16 to IP

Physical and Microstructural Properties of NiO‐ and Ni‐YSZ Composite Thin Films Fabricated by Pulsed‐Laser Deposition at T≤700°C

“…In spite of this interesting finding, however, this approach seems to have significant problems to be used for fabricating nanoporous cermet electrodes. As observed in other reports on low‐temperature processed thin film nanocoomposites, 13–18 massive metal agglomeration was observed after the reduction. In Fig.…”

“…Especially, the latter was studied intensively in the field of the micro‐SOFC by using thin film deposition techniques such as sputtering, 15–18 pulsed‐laser deposition (PLD), 14 and spray pyrolysis 13,14 because the ceramic network in the nanocomposite was expected to retain the dispersion of the metal particles as in conventional SOFCs 1,19 . However, in contrast to expectation, massive metal phase agglomeration was observed after reduction or thermal treatment regardless of the deposition methods, which leads to the loss of conductivity and poor high‐temperature stability of electrodes 13,15–18 . It was postulated that the larger driving force for agglomeration associated with smaller metal grains is the main cause of the severe agglomeration 13,17 .…”

“…11 Currently, most of thin film SOFCs use single-phase noble metal electrodes such as porous Pt 4,7,11,12 as nanostructured electrodes; however, metal coarsening at operating temperatures eventually leads to serious problems such as the reduction of the triple phase boundary, loss of connectivity by the isolation of the coarsened metal agglomerates, and delamination of the electrode layer. 11,12 To prevent metal coarsening, composite electrodes including bimetallic alloys 12 and ceramic-metal composites [13][14][15][16][17][18] were investigated. Especially, the latter was studied intensively in the field of the micro-SOFC by using thin film deposition techniques such as sputtering, [15][16][17][18] pulsed-laser deposition (PLD), 14 and spray pyrolysis 13,14 because the ceramic network in the nanocomposite was expected to retain the dispersion of the metal particles as in conventional SOFCs.…”

Suppression of Ni agglomeration in PLD fabricated Ni-YSZ composite for surface modification of SOFC anode

“…1,10 To obtain nano-structured electrodes for thin electrolytes, most of thin film base SOFCs use single phase noble metal electrodes such as porous Pt fabricated by sputtering, 4,6,8,10,12 but the metal coarsening at operating temperatures eventually leads to serious problems such as the reduction of the triple phase boundary length and thus degradation of the cell performance. 10,12 Therefore, ceramic-metal composites (cermets) fabricated by thin film deposition methods 1,[13][14][15][16][17][18][19][20][21][22] were investigated actively to prevent the metal coarsening since the ceramic network in the nano-composite is expected to retain the excessive metal grain growth 6,23 as in conventional SOFCs. In some cases, desirable microstructures, such as a nano-porous structure and an interpenetrating nano-composite structure, 19,22 as well as promising electrochemical performances, such as lower overpotentials and electrode resistances, [20][21][22] were reported.…”

“…In some cases, desirable microstructures, such as a nano-porous structure and an interpenetrating nano-composite structure, 19,22 as well as promising electrochemical performances, such as lower overpotentials and electrode resistances, [20][21][22] were reported. However, in many cases, even more massive metal phase agglomeration was observed after the reduction or thermal treatments of the thin film composites regardless of the deposition methods, 1,13,[15][16][17][18] which leads to the loss of the connectivity and the poor high temperature stability of electrodes.…”