Faceted Grain Boundaries in Al₂O₃

Abstract

Different types of faceted grain boundaries in commercial poly-crystalline Altoz were examined. Three distinct cases, namely the basal twin, the rhombohedra1 twin, and other special highangle grain boundaries, are discussed, comparing theoretical models and experimental observations. It is shown that the faceting of the boundaries can be associated with their migration. A mechanism for the separation of a 2 = 13 grain houndary from a pinning void, small grain, or second-phase particle is illustrated. It is also shown experimentally that faceting of high-angle boundaries can occur on a scale of -5 nm, and that, theoretically, faceting most likely also occurs on an atomistic scale. Throughout the theoretical analysis the basal plane is predicted to be a favored facet plane, which is confirmed by experimental observation.

Molecular Dynamics Simulations of Calcium Aluminosilicate Intergranular Films on (0001) Al2O3 Facets

“…5,6 Because the solubility limits of silicon and calcium in Al 2 O 3 are very low, these impurities tend to accumulate in intergranular regions. 3,[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] During sintering, the impurities form a liquid phase that vitrifies on cooling. Several authors have reported faceted grains in contact with glassy IGFs.…”

“…Several authors have reported faceted grains in contact with glassy IGFs. 3,11,[13][14][15][16][17][18][19][20][21][22][23][24] Facets of the basal (0001) plane and other low-index planes have been observed during sintering. Faceting of grains indicates a lower interface energy for the planes that facet relative to adjacent planes or relatively slower growth rates of the faceted planes.…”

“…Anisotropic and abnormal grain growth of faceted grains has been reported in several studies. [3][4][5][6]8,10,11,[13][14][15][16][17][18][19][20][21][23][24][25][26][27][28] Abnormal grain growth occurs when the growth rates of certain grains are much higher than the growth rates of other grains. The growth rates of grains containing relatively low-energy grain boundaries are high, because these grain boundaries would extend to reduce the free energy of the system.…”

Pt‐Al2O3 interfaces in cofired ceramics for use in miniaturized neuroprosthetic implants

“…In addition, faceted particulates could be observed in the alumina [Figure (b)] and are common in high purity alumina . Intragranular pores are constructed as the Al 2 O 3 crystal grains as they present a dislocation loop where the pore is unpinned from the dislocation line in order to minimize the energy along the boundary …”

Investigating the Structure‐Property Relationships at Grain Boundaries in MgO Using Bond‐Valence Pair Potentials and Multiple Scattering Analysis

“…The usual methods of investigating the structure-property relationships of grain boundaries are either phase contrast imaging [6][7][8][9] in the transmission electron microscope (TEM) or Z-contrast imaging [10][11][12] in the scanning transmission electron microscope (STEM). While both of these techniques allow a structural model to be determined, they do not necessarily allow us to formulate the properties of the boundary, as compo-sitional and electronic structure fluctuations can also be important.…”