Analysis of reactions during sintering of CuO-doped 3Y-TZP nano-powder composites

3Y-TZP (yttria-doped tetragonal zirconia) and CuO nano powders were prepared by co-precipitation and copper oxalate complexation–precipitation techniques, respectively. During sintering of powder compacts (8 mol% CuO-doped 3Y-TZP) of this two-phase system several solid-state reactions clearly influence densification behaviour. These reactions were analysed by several techniques like XPS, DSC/TGA and high-temperature XRD. A strong dissolution of CuO in the 3Y-TZP matrix occurs below 600 °C, resulting in significant enrichment of CuO in a 3Y-TZP grain-boundary layer with a thickness of several nanometres. This “transient” liquid phase strongly enhances densification. Around 860 °C a solid-state reaction between CuO and yttria as segregated to the 3Y-TZP grain boundaries occurs, forming Y2Cu2O5. This solid-state reaction induces the formation of the thermodynamic stable monoclinic zirconia phase. The formation of this solid phase also retards densification. Using this knowledge of microstructural development during sintering it was possible to obtain a dense nano–nano composite with a grain size of only 120 nm after sintering at 960 °C

La(Ni,Fe)O3 Stability in the Presence of Chromia—A Solid-State Reactivity Study

The perovskite $La(Ni_{0.6}Fe_{0.4})O_3$ (LNF) is a candidate material for the electrochemically active cathode layer, the cathode current collecting layer, and/or the interconnect protective coating in intermediate temperature solid oxide fuel cells (IT-SOFCs) operated at . Since these operating temperatures enable the use of relatively cheap interconnect materials such as chromia-forming ferritic stainless steel, investigation of the chemical stability of LNF in the presence of chromium species is of importance. This study demonstrates that LNF is chemically unstable at when it is in direct contact with $Cr_2O_3$. It has been observed that Cr enters the perovskite phase, replacing first Ni and then Fe, already after 200h. At 600°C, however, only minor reaction products were detected after 1000h exposure to $Cr_2O_3$. Although this is a promising result, long-term testing under fuel cell operating conditions at 600°C is needed to prove that LNF is a viable IT-SOFC material

Impact of Cr-poisoning on the conductivity of different LaNi0.6Fe0.4O3 cathode microstructures

The microstructure of porous LaNi0.6Fe0.4O3 (LNF) layers has a significant influence on the degree of the Cr-poisoning impact. The increase in the in-plane resistance and Cr accumulation in poisoned LNF-layers has been correlated with microstructural features. The Cr-poisoning impact is more severe in the case of a microstructure characterized by finer particles, higher porosity and larger particle surface area

Enhanced surface diffusion through termination conversion during epitaxial SrRuO3 growth

During the initial growth of the ferromagnetic oxide SrRuO3 on TiO2-terminated SrTiO3, we observe a self-organized conversion of the terminating atomic layer from RuO2 to SrO. This conversion induces an abrupt change in growth mode from layer by layer to growth by step advancement, indicating a large enhancement of the surface diffusivity. This growth mode enables the growth of single-crystalline and single-domain thin films. Both conversion and the resulting growth mode enable the control of the interface properties in heteroepitaxial multilayer structures on an atomic level

Impact of Cr-poisoning on the conductivity of LaNi0.6Fe0.4O3

This study demonstrates the significant impact of Cr on the electronic conductivity of a LaNi0.6Fe0.4O3 (LNF) porous cathode layer at 800 °C. Vapor transport of Cr-species, originating from a porous metallic foam, and subsequent reaction with LNF, results in a decrease of the electronic conductivity of the LNF-layer. Cr has been detected throughout the entire cross-section of a 16 μm thick LNF layer, while Ni, besides its compositional distribution in the LNF layer, has also been found in enriched spots forming Ni-rich metal oxide crystals. Transmission electron microscopy revealed that Cr is gradually incorporated into the LNF-grains, while Ni is proportionally expelled. Electron diffraction performed in the center of a sliced grain showed the initial rhombohedral crystal structure of LNF, whereas diffraction performed close to the edge of the grain revealed the orthorhombic perovskite crystal structure, indicating a Cr-enriched perovskite phase. Progressive Cr deposition and penetration into the LNF grains and necks explains the electronic conductivity deterioration. The impact of Cr-poisoning on the electronic conductivity of the LNF porous layer is considerably smaller at 600 °C than at 800 °C

Fabrication of arrays of gold islands on self-assembled monolayers using pulsed laser deposition through nanosieves

Sandwich structures of gold-self-assembled monolayer-gold were prepared by deposition of gold on alkylthiolate self-assembled monolayers on polycrystalline gold, using pulsed laser deposition (PLD) through a nanosieve. The arrays of sandwiches, around 600 nm in diameter, approximately 10 nm high, and spaced 1.6 ím apart, were analyzed using tapping mode atomic force microscopy. Electrochemical copper deposition experiments showed that of the islands deposited on octadecanethiolate monolayers about 15% were electrically insulated from the bottom gold electrode. This means that PLD is a suitable technique for the fabrication of metal-SAM-metal sandwich structures

Growth mode transition from layer-by-layer to step-flow during the growth of heteroepitaxial SrRu)3 on (001) SrTiO3

We have observed the growth mode transition from two-dimensional (2D) layer-by-layer to step-flow in the earliest stage growth of heteroepitaxial SrRuO3 thin films on TiO2-terminated (001) SrTiO3 substrates by in situ high pressure reflective high energy electron diffraction (RHEED) and atomic-force microscopy. There is no RHEED intensity recovery after each laser pulse in the first oscillation when the growth mode is 2D layer-by-layer. On the other hand, it is getting more pronounced in the second oscillation, and finally reaches a dynamic steady state in which the growth mode is completely changed into the step-flow mode. The origin of the growth mode transition can be attributed to a change in the mobility of adatoms and switching the surface termination layer from the substrate to the film. SrRuO3 thin films with an atomically smooth surface grown by atomic layer control can be used in oxide multilayered heterostructure devices