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Han, Wei; Maus‐Friedrichs, W.; Lilienkamp, G.; Kempter, V.; Helmbold, J.; Gömann, Karsten; Borchardt, Günter

doi:10.1023/a:1020850101504

Cited by 19 publications

(13 citation statements)

References 18 publications

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“…The change from the n-type character to the p-type character in ALD-SrTiO 3 might be due to the existence of surface defects in ALD-SrTiO 3 , such as SrO segregation (chemical nonuniformity) and crystal orientation nonuniformity. The main component of surface islands is known to be SrO segregation; however, these islands do not consist of pure stoichiometric SrO but is most likely influenced by SrO 2 contribution [10]. Therefore, SrO islands can have p-type character owing to SrO 2 contribution.…”

Section: Resultsmentioning

confidence: 99%

Oxygen sensitivity of SrTiO3 thin film prepared using atomic layer deposition

Hara

Ishiguro

2009

Sensors and Actuators B: Chemical

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Section: Resultsmentioning

confidence: 99%

Oxygen sensitivity of SrTiO3 thin film prepared using atomic layer deposition

Hara

Ishiguro

2009

Sensors and Actuators B: Chemical

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“…21 SrO segregation layers on SrTiO 3 were also found to change the valence band structure on the surface in other studies using XPS, UPS and metastable impact electron spectroscopy. 23,24 Thus, we conclude that the Sr 30 segregation layer in the form of SrO on the surface of STF100 is the reason for the additional state located deeper in the valence band (in O 2p). This result is consistent with the conclusion we obtained about the formation of a SrO phase on the STF surfaces in section 3.3.1.…”

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confidence: 79%

Impact of Sr segregation on the electronic structure and oxygen reduction activity of SrTi1−xFexO3 surfaces

Chen

Jung

Cai

et al. 2012

Energy Environ. Sci.

194

180

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The correlation between the surface chemistry and electronic structure is studied for SrTi 1-x Fe x O 3 (STF), as a model perovskite system, to explain the impact of Sr segregation on the oxygen reduction activity of cathodes in solid oxide fuel cells. Dense thin films of SrTi 0.95 Fe 0.05 O 3 (STF5), SrTi 0.65 Fe 0.35 O 3 (STF35) and SrFeO 3 (STF100) were investigated using a coordinated combination of surface probes. Composition, chemical binding, and valence band structure analysis using angle-resolved x-ray photoelectron 10 spectroscopy showed that Sr enrichment increases on the STF film surfaces with increasing Fe content. In situ scanning tunnelling microscopy / spectroscopy results proved the important and detrimental impact of this cation segregation on the surface electronic structure at high temperature and in oxygen environment. While no apparent band gap was found on the STF5 surface due to defect states at 345 o C and 10 -3 mbar of oxygen, the surface band gap increased with Fe content, 2.5 ± 0.5 eV for STF35 and 3.6 ± 0.6 eV for 15 STF100, driven by a down-shift in energy of the valence band. This trend is opposite to the dependence of the bulk STF band gap on Fe fraction, and is attributed to the formation of a Sr-rich surface phase in the form of SrO x on the basis of the measured surface band structure. The results demonstrate that Sr segregation on STF can deteriorate oxygen reduction kinetics through two mechanisms -inhibition of electron transfer from bulk STF to oxygen species adsorbing onto the surface, and the smaller 20 concentration of oxygen vacancies available on the surface for incorporating oxygen into the lattice. IntroductionBecause of their high efficiency and fuel flexibility, solid oxide fuel cells (SOFCs) offer the potential to contribute significantly to a clean energy infrastructure 1, 2 . However, their high working 25 temperatures (>800 o C) impose challenges due to accelerated materials degradation and high cost. The lowering of the working temperature has, therefore, become a strong focus of research. 3 At reduced temperatures (<700 o C), slow Oxygen Reduction Reaction (ORR) kinetics at the cathode become a major barrier to 30 the implementation of high performance SOFCs. To rationally design new cathode materials with high ORR activity, it is necessary to understand the governing ORR mechanisms and identify key descriptors of the cathode materials that directly control ORR activity. The strength of oxygen adsorption and the 35 energy barriers to oxygen dissociation, reduction and incorporation are believed to be the processes that determine oxygen reduction activity on perovskite oxides. 4,5 The energetics of these processes depends, in part, on the cathode electronic structure. In transition metal catalysis, the d-40 band structure 6 is a well-established descriptor of ORR activity. However, the applicability of the d-band model to perovskite oxide SOFC cathodes is limited by their complex surface chemistry (an anion and two cation sublattices), the role of oxygen vacan...

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“…Thermal treatment under oxidizing conditions (air or oxygen atmosphere) leads to the formation of SrO-enriched phases on top of the surface [5,10,11,12,13,14]. The underlying process leading to the Sr enrichment is discussed within the framework of point defect chemistry formalism.…”

Section: Introductionmentioning

confidence: 99%

Nanostructures on La-doped SrTiO3 surfaces

et al. 2003

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SrTiO(3)(100) single crystals with high donor dopant concentrations (5 at% La) were annealed at 1000 degrees C for up to 150 h in ultrahigh vacuum (UHV). By applying scanning tunneling microscopy (STM) nanostructures are observed on top of the surface with typical diameters of 20 nm and typical heights of 8 nm. To characterize their electronic structure and chemical composition, the surface was analyzed by metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS), scanning tunneling spectroscopy (STS), and depth profiling Auger electron spectroscopy (AES). Investigations of the stoichiometry suggest that the secondary phases consist of LaTiO(3). We present a defect chemistry model which attempts to explain the observed effects.

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Untitled

Cited by 19 publications

References 18 publications

Oxygen sensitivity of SrTiO3 thin film prepared using atomic layer deposition

Oxygen sensitivity of SrTiO3 thin film prepared using atomic layer deposition

Impact of Sr segregation on the electronic structure and oxygen reduction activity of SrTi1−xFexO3 surfaces

Nanostructures on La-doped SrTiO3 surfaces

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