Structural and electronic properties of Σ7 grain boundaries in α-Al2O3

Guhl, Hannes; Lee, Hak Sung; Tangney, Paul; Foulkes, W. M. C.; Heuer, A. H.; Nakagawa, Takeshi; Ikuhara, Yuichi; Finnis, Michael W.

doi:10.1016/j.actamat.2015.07.042

Cited by 27 publications

(30 citation statements)

References 32 publications

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“…). Using the atomic coordinates of the calculated lowest energy structures of the two Σ7 bi‐crystal boundaries as input for HREM image simulations, reasonable agreement with the experimental HREM images was obtained …”

Section: The Atomic and Electronic Structures Of σ7 Grain Boundariesmentioning

confidence: 66%

“…Lowest energy structure of a Σ7m symmetric tilt bi‐crystal boundary in Al 2 O 3. The computed and experimental grain‐boundary energies are 1.84 and 1.29 J/m 2 , respectively …”

Section: The Atomic and Electronic Structures Of σ7 Grain Boundariesmentioning

confidence: 91%

“…shows that the absolute magnitudes of the tracer data for D b Al and D b oxy are comparable. (Comparable magnitudes of D b Al and D b oxy are also inferred from the kinetics of Al 2 O 3 scale formation in alloys lacking Reactive Elements …”

Section: Enhanced Grain‐boundary Diffusion In Al2o3mentioning

confidence: 93%

“…We now review recent DFT calculations of the atomic structure and DOS (density of states) of nominally undoped Σ7{2

\overset{3}{true}

10} (Σ7m) and Σ7{4

\overset{5}{true}

10} (Σ7a) bi‐crystal boundaries, and provide DFT results for a Σ7{2

\overset{3}{true}

10} boundary containing a Y 2 O 3 segregant (As noted already, and as is shown in Fig. below, the Σ7a boundary exhibited much faster oxygen grain‐boundary diffusivities than did the Σ7m boundary …”

Section: The Atomic and Electronic Structures Of σ7 Grain Boundariesmentioning

confidence: 95%

“…The computed and experimental grain‐boundary energies are 2.11 and 0.97 J/m 2 . This boundary is “wider” and less well “ordered” than the Σ7m boundary …”

Section: The Atomic and Electronic Structures Of σ7 Grain Boundariesmentioning

confidence: 98%

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The Band Structure of Polycrystalline Al₂O₃ and Its Influence on Transport Phenomena

et al. 2016

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The electronic (band) structure of polycrystalline Al2O3, in particular the density of near‐band edge grain‐boundary localized states, plays a significant role in a host of high‐temperature phenomena, including sintering, high‐temperature creep, oxygen permeability in dense “dry” Al2O3 ceramics, and Al2O3 scale formation on Al2O3 scale‐forming alloys. All these phenomena involve creation or annihilation of charged point defects (vacancies and/or interstitials) at grain boundaries and interfaces, and must of necessity involve electrons and holes. Thus, the density of states associated with grain boundaries in Al2O3 assume great importance, and has been calculated using DFT for both nominally undoped and Y‐doped Σ7 bi‐crystal boundaries. These quantum mechanical calculations must be taken into account when considering why Y2O3 segregation to Al2O3 grain boundaries is so effective in enhancing high‐temperature creep resistance of polycrystalline Al2O3, and in understanding the reactive element effect in Al2O3 scale‐forming alloys. Finally, a case will be made that grain‐boundary diffusion is mediated by the migration of a class of grain‐boundary ledge defects called disconnections, which are characterized by a step height h and a Burgers vector b.

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Section: The Atomic and Electronic Structures Of σ7 Grain Boundariesmentioning

confidence: 66%

“…Lowest energy structure of a Σ7m symmetric tilt bi‐crystal boundary in Al 2 O 3. The computed and experimental grain‐boundary energies are 1.84 and 1.29 J/m 2 , respectively …”

Section: The Atomic and Electronic Structures Of σ7 Grain Boundariesmentioning

confidence: 91%

Section: Enhanced Grain‐boundary Diffusion In Al2o3mentioning

confidence: 93%

“…We now review recent DFT calculations of the atomic structure and DOS (density of states) of nominally undoped Σ7{2

\overset{3}{true}

10} (Σ7m) and Σ7{4

\overset{5}{true}

10} (Σ7a) bi‐crystal boundaries, and provide DFT results for a Σ7{2

\overset{3}{true}

Section: The Atomic and Electronic Structures Of σ7 Grain Boundariesmentioning

confidence: 95%

“…The computed and experimental grain‐boundary energies are 2.11 and 0.97 J/m 2 . This boundary is “wider” and less well “ordered” than the Σ7m boundary …”

Section: The Atomic and Electronic Structures Of σ7 Grain Boundariesmentioning

confidence: 98%

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The Band Structure of Polycrystalline Al₂O₃ and Its Influence on Transport Phenomena

et al. 2016

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Atomistic grain boundary migration in Al₂O₃

Feng

Shibata

Ikuhara

2023

Int J Ceramic Engine & Sci

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Grain boundary (GB) migration is one of the most important phenomena in materials science, which plays a key role in modifying the microstructures and properties of polycrystalline ceramic materials. Understanding how GB migrates is thus a fundamental and critical issue for future ceramic material design. While the understanding of GB atomic structures has evolved significantly over the past several decades due to the progress of atomic‐resolution electron microscopy and atomistic simulation, the understanding of the atomistic grain boundary migration is still lacking. The present article briefly reviews our recent progress on the direct observation of atomistic GB migration in ceramic material by atomic‐resolution scanning transmission electron microscopy (STEM). Using Al2O3 as a model material, we found that the atomistic GB migration proceeds with atom shuffling accompanied by GB structural change and/or nucleation of disconnection, which is highly dependent on the GB atomic structures.

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Reactive Element Effects in High-Temperature Alloys Disentangled

2019

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Reactive elements-REs-are decisive for the longevity of high-temperature alloys. This work joins several previous efforts to disentangle various RE effects in order to explain apparently contradicting experimental observations in alumina forming alloys. At 800-1000 °C, "messy" aluminum oxy-hydroxy-hydride transients initially formed due to oxidation by H 2 O which in turn undergo secondary oxidation by O 2. The formation of the transient oxide becomes supported by dispersed RE oxide particles acting as water equivalents. At higher temperatures, electron conductivity in impurity states owing to oxygen vacancies in grain boundaries (GBs) becomes increasingly relevant. These channels are subsequently closed by REs pinning the said vacancies. The universality of the emerging understanding is supported by a comparative first-principles study by means of density functional theory addressing RE(III): Sc 2 O 3 , Y 2 O 3 , and La 2 O 3 , and RE(IV): TiO 2 , ZrO 2 , and HfO 2, that upon reaction with water, co-decorate a generic GB model by hydroxide and RE ions. At 100% RE coverage, the GB model becomes relevant at both temperature regimes. Based on reaction enthalpy ΔH r considerations, "messy" aluminum oxy-hydroxyhydride transients are accessed in both classes. Larger variations in ΔH r are found for RE(III)-decorated alumina GBs as compared to RE(IV). For RE(III), correlation with GB width is found, increasing with increased ionic radius. Similarly, upon varying RE(IV), minor changes in stability correlate with minor structural variations. GB decorations by Ce(III) and Ce(IV) further consolidate the emerging understanding. The findings are used to discuss experimental observations that include impact of co-doping by RE(III) and RE(IV).

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Structural and electronic properties of Σ7 grain boundaries in α-Al2O3

Cited by 27 publications

References 32 publications

The Band Structure of Polycrystalline Al₂O₃ and Its Influence on Transport Phenomena

The Band Structure of Polycrystalline Al₂O₃ and Its Influence on Transport Phenomena

Atomistic grain boundary migration in Al₂O₃

Reactive Element Effects in High-Temperature Alloys Disentangled

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Structural and electronic properties of Σ7 grain boundaries in α-Al2O3

Cited by 27 publications

References 32 publications

The Band Structure of Polycrystalline Al2O3 and Its Influence on Transport Phenomena

The Band Structure of Polycrystalline Al2O3 and Its Influence on Transport Phenomena

Atomistic grain boundary migration in Al2O3

Reactive Element Effects in High-Temperature Alloys Disentangled

Contact Info

Product

Resources

About

The Band Structure of Polycrystalline Al₂O₃ and Its Influence on Transport Phenomena

The Band Structure of Polycrystalline Al₂O₃ and Its Influence on Transport Phenomena

Atomistic grain boundary migration in Al₂O₃