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The Band Structure of Polycrystalline Al 2 O 3 and Its Influence on Transport Phenomena
Author(s) -
Heuer Arthur H.,
Zahiri Azar Maryam,
Guhl Hannes,
Foulkes Matthew,
Gleeson Brian,
Nakagawa Tsubasa,
Ikuhara Yuichi,
Finnis Mike W.
Publication year - 2016
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.14149
Subject(s) - grain boundary , materials science , condensed matter physics , crystallite , grain boundary diffusion coefficient , creep , crystallographic defect , grain boundary strengthening , sintering , crystallography , metallurgy , chemistry , microstructure , physics
The electronic (band) structure of polycrystalline Al 2 O 3 , 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” Al 2 O 3 ceramics, and Al 2 O 3 scale formation on Al 2 O 3 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 Al 2 O 3 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 Y 2 O 3 segregation to Al 2 O 3 grain boundaries is so effective in enhancing high‐temperature creep resistance of polycrystalline Al 2 O 3 , and in understanding the reactive element effect in Al 2 O 3 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.