Accommodation of Excess Oxygen in Group II Monoxides

Middleburgh, Simon C.; Lagerlöf, K.P.D.; Grimes, Robin W.

doi:10.1111/j.1551-2916.2012.05452.x

Cited by 65 publications

(37 citation statements)

References 28 publications

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“…Previous thermodynamic analysis of Sr-oxide phases have shown that under these conditions SrO 2 is stable. 65 At higher temperatures (>527°C) 65 18 Figure S8 (a).…”

Section: Near-surface Atomic Structure and Composition By Stem And Edmentioning

confidence: 97%

Segregated Chemistry and Structure on (001) and (100) Surfaces of (La_1–xSr_x)₂CoO₄ Override the Crystal Anisotropy in Oxygen Exchange Kinetics

Chen¹,

et al. 2015

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Attaining fast oxygen exchange kinetics on perovskite and related mixed ionic and electronic conducting oxides is critical for enabling their applications in electrochemical energy conversion systems. This study focuses on understanding the relationship between surface chemistry and the surface oxygen exchange kinetics on epitaxial films made of (La 1-x Sr x ) 2 CoO 4 , a prototypical Ruddlesden-Popper structure that is considered as a promising cathode material for fuel cells. The effects of crystal orientation on the surface composition, morphology, oxygen diffusion and surface exchange kinetics were assessed by combining complementary surface-sensitive analytical techniques, specifically low energy ion scattering, x-ray photoelectron spectroscopy, Auger electron spectroscopy, scanning transmission electron microscopy, atomic force microscopy and secondary ion mass spectroscopy. The films were grown in two different crystallographic orientations, (001) and (100), and with two different Sr compositions, at x=0.25 (LSC25) and 0.50 (LSC50), by using pulsed laser deposition. In the as-prepared state, a Sr enriched layer at the top surface and a Co enriched subsurface layer were found on films with both orientations. After annealing at elevated temperatures in oxygen, the Sr enrichment increased, followed by clustering into Sr-rich secondary phase particles. Both the LSC25 and LSC50 films showed anisotropic oxygen diffusion kinetics, with up to 20 times higher oxygen diffusion coefficient along the (ab) plane compared that along the c-axis at 400-500 o C. However, no dependence of surface oxygen exchange coefficient was found on the crystal orientation. This result indicates that the strong Sr segregation at the surface overrides the effect of the structural anisotropy that was also expected for the surface exchange kinetics. The larger presence of Co cations exposed at the LSC25 surface compared to that at the LSC50 surface is likely the reason for the faster oxygen surface exchange kinetics on LSC25 compared to LSC50. This work demonstrated the critical role of surface chemistry on the oxygen exchange kinetics on perovskite related oxides, which are thus far under-explored at elevated temperatures, and provides a generalizable approach to probe the surface chemistry on other catalytic complex oxides.

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“…Previous thermodynamic analysis of Sr-oxide phases have shown that under these conditions SrO 2 is stable. 65 At higher temperatures (>527°C) 65 18 Figure S8 (a).…”

Section: Near-surface Atomic Structure and Composition By Stem And Edmentioning

confidence: 97%

Segregated Chemistry and Structure on (001) and (100) Surfaces of (La_1–xSr_x)₂CoO₄ Override the Crystal Anisotropy in Oxygen Exchange Kinetics

Chen¹,

et al. 2015

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“…The relative vacancy formation energies in Zr 2 AlC are different from Cr 2 AlC and can be summarized as follows:Other MAX phases such as Ti 3 AlC 2 and Ti 3 SiC 2 exhibit a trend in vacancy formation similar to Zr 2 AlC 13, 31 . However, the results clearly depend on the synthesis conditions, as shown in the SI (Figures S3–S6).…”

Section: Resultsmentioning

confidence: 99%

Point defect formation in M2AlC (M = Zr,Cr) MAX phases and their tendency to disorder and amorphize

Shah

Bristowe

2017

Sci Rep

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First principles calculations are performed on Zr2AlC and Cr2AlC MAX phases to compare their ability to accommodate point defects under irradiation. Interatomic bonding is stronger in Cr2AlC than Zr2AlC but contrary to expectation Zr2AlC exhibits higher vacancy and antisite pair formation energies. However, interstitials and Frenkel defects are generally more difficult to form in Cr2AlC. The results are attributed to the mixed covalent/ionic/metallic nature of the bonding. Detailed comparison of all the energies suggests that the preferred defects in Zr2AlC and Cr2AlC are the VAl+Ali Frenkel and CrAl+AlCr antisite respectively. Thus the potential response of the two phases to irradiation is different and taking account of other competing defects it is suggested that Zr2AlC is less susceptible to amorphization.

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“…During radiation damage the produced point defects may either recombine or reside on alternative lattice site forming antisite defects [61]. From a physical viewpoint a low energy antisite formation energy means that a high proportion of residual defects will remain in the material as typically the conversion of an interstitial into an antisite will result to a net reduction of defect mobility [61]. The antisite formation mechanisms are:…”

Section: Antisite Defect Formationmentioning

confidence: 99%

Section: Implications Of Defect Processesmentioning

confidence: 99%

“…The radiation performance of materials is dependent upon their propensity to form and accommodate point defects [60,61]. A high concentration of defects may lead to the destabilization of the MAX phase (or any material) and may result to volume changes and microcracking [61][62][63]. It is established that displacive radiation can result to an athermal concentration of Frenkel pairs and therefore the radiation tolerance of materials is linked to their ability to resist the formation of significant populations of Frenkel and/or antisite) defects.…”

Section: Implications Of Defect Processesmentioning

confidence: 99%

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Mechanical behavior, bonding nature and defect processes of Mo2ScAlC2: A new ordered MAX phase

Hadi

Naqib

Christopoulos

et al. 2017

Journal of Alloys and Compounds

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In the present study we employed density functional theory calculations to investigate the mechanical behavior, bonding nature and defect processes of the new ordered MAX phase Mo 2 ScAlC 2 . The mechanical stability of the compound is verified with its single crystal elastic constants. The new phase Mo 2 ScAlC 2 is anticipated to be prone to shear along the crystallographic b and c axes, when a rational force is applied to the crystallographic a axis. The compressibility along the 001 direction under uniaxial stress is expected to be easier in Mo 2 ScAlC 2 . Additionally, the volume deformation should be easier in Mo 2 ScAlC 2 than the isostructural Mo 2 TiAlC 2 . Mo 2 ScAlC 2 is predicted to behave in a brittle manner. Due to its higher Debye temperature, Mo 2 ScAlC 2 is expected to be thermally more conductive than Mo 2 TiAlC 2 . The cross-slip pining procedure should be significantly easier in Mo 2 ScAlC 2 as compared to Mo 2 TiAlC 2 . The new ordered MAX phase Mo 2 ScAlC 2 has a mixed character of strong covalent and metallic bonding with limited ionic nature. Both Mo-C and Mo-Al bonds are expected to be more covalent in Mo 2 ScAlC 2 than those of Mo 2 TiAlC 2 . The level of covalency of Sc-C bond is somewhat low compared to a similar bond Ti-C in Mo 2 ScAlC 2 . Due to its reduced hardness Mo 2 ScAlC 2 , it should be softer and more easily machinable compared to Mo 2 TiAlC 2 . Fermi surface topology of the new compound is formed mainly due to the low-dispersive Mo 4d-like bands. The intrinsic defect processes reveal that the level of radiation tolerance in Mo 2 ScAlC 2 is not as high as in other MAX phases such as Ti 3 AlC 2 .

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Accommodation of Excess Oxygen in Group II Monoxides

Cited by 65 publications

References 28 publications

Segregated Chemistry and Structure on (001) and (100) Surfaces of (La_1–xSr_x)₂CoO₄ Override the Crystal Anisotropy in Oxygen Exchange Kinetics

Segregated Chemistry and Structure on (001) and (100) Surfaces of (La_1–xSr_x)₂CoO₄ Override the Crystal Anisotropy in Oxygen Exchange Kinetics

Point defect formation in M2AlC (M = Zr,Cr) MAX phases and their tendency to disorder and amorphize

Mechanical behavior, bonding nature and defect processes of Mo2ScAlC2: A new ordered MAX phase

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Accommodation of Excess Oxygen in Group II Monoxides

Cited by 65 publications

References 28 publications

Segregated Chemistry and Structure on (001) and (100) Surfaces of (La1–xSrx)2CoO4 Override the Crystal Anisotropy in Oxygen Exchange Kinetics

Segregated Chemistry and Structure on (001) and (100) Surfaces of (La1–xSrx)2CoO4 Override the Crystal Anisotropy in Oxygen Exchange Kinetics

Point defect formation in M2AlC (M = Zr,Cr) MAX phases and their tendency to disorder and amorphize

Mechanical behavior, bonding nature and defect processes of Mo2ScAlC2: A new ordered MAX phase

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Segregated Chemistry and Structure on (001) and (100) Surfaces of (La_1–xSr_x)₂CoO₄ Override the Crystal Anisotropy in Oxygen Exchange Kinetics

Segregated Chemistry and Structure on (001) and (100) Surfaces of (La_1–xSr_x)₂CoO₄ Override the Crystal Anisotropy in Oxygen Exchange Kinetics