Grain Boundary Structures in High-Purity Al2O3 Bicrystals Grown From the Melt

1985 ◽  
Vol 60 ◽  
Author(s):  
P.A. Morris ◽  
R.L. Coble
Keyword(s):  
Grain Boundary ◽  
High Purity ◽  
Ceramic Materials ◽  
Boundary Region ◽  
Boundary Structure ◽  
Second Phase ◽  
Stem Analysis ◽  
Tilt Boundaries ◽  
Boundary Characteristics ◽  
Structure Investigations

AbstractThe clean room processing, firing and crystal growth techniques required to produce high-purity Al2O3 crystals and bicrystals with [2110] tilt boundaries near low Σ misorientations are described. The chemical analysis requirements for high-purity ceramic materials are discussed. The boundary characteristics of the θ=33.2°, near Σ = 11, misorientation and the applicability of the CSL model to describe the observed facet planes is determined. The periodicity of the dislocations present in the boundary is 21 nm. STEM analysis of the grain boundary region indicates no second phase or detectable impurity concentrations. The importance of gra in boundary structure investigations in high-purity materials and of chemically well-characterized boundaries is discussed.

Disruption of Dislocation Cores at Grain Boundary in Nb-Doped SrTiO3 Bicrystals

2007 ◽  
Vol 558-559 ◽  
pp. 869-872
Author(s):  
S.Y. Choi ◽  
J.P. Buban ◽  
Naoya Shibata ◽  
Takahisa Yamamoto ◽  
Yuichi Ikuhara
Keyword(s):  
Grain Boundary ◽  
Tilt Angle ◽  
Structural Changes ◽  
Boundary Region ◽  
Boundary Structure ◽  
Regular Array ◽  
Density Of Dislocations ◽  
Discrete Dislocation ◽  
Grain Boundary Structure ◽  
Oriented Region

Bicrystals of Nb-doped SrTiO3, having tilt angles of 4o~18 o with respect to [001], were prepared by joining two single crystals at 1873 K and then investigated to identify the effect of tilt angle on the grain boundary structure. The boundaries consisted of a regular array of dislocations but the positioning of cores along the boundary was found to be changed from a line to a zigzag as a tilt angle was increased up to 10o. The 14° - tilted boundary exhibited two kinds of boundary region exist at the same grain boundary; (1) the discrete cores region as observed in 4° ~ 10° - tilted boundaries and (2) the randomly oriented region as found in the 18° boundary. Thus it was observed that the structure of low-angle tilt boundary changed from the discrete dislocation structure to the randomly oriented structure as a tilt angle increases. These structural changes at the grain boundaries are considered to be related to a minimization of strain due to the high density of dislocations.

Atomic and Electronic Structures of Grain Boundary in Chemical Vapor Deposited Diamond Thin Film

1995 ◽  
Vol 416 ◽  
Author(s):  
Y. Zhang ◽  
H. Ichinose ◽  
Y. Ishida ◽  
K. Ito ◽  
M. Nakanose
Keyword(s):  
Grain Boundary ◽  
Energy Loss ◽  
Electron Energy ◽  
Electronic Structures ◽  
Chemical Vapor ◽  
High Resolution Electron Microscopy ◽  
Boundary Structure ◽  
Atomic Structures ◽  
Tilt Boundaries ◽  
Electron Energy Loss

ABSTRACTHigh resolution electron microscopy and electron energy-loss spectrometry were used to investigate both atomic and electronic structures of grain boundaries in diamond thin films grown by chemical vapor deposition. The atomic structures of {112}σ3 and {114}σ9 <110= tilt boundaries in diamond show different features from those in other diamond structure semiconductors. The electron energy-loss spectra recorded from the grain boundary regions show extra intensity near the energy-loss corresponding to carbon 1s-to-π*; transition, as compared to the spectra recorded from neighboring crystalline regions. This gives the evidence that the dangling bonds are not fully reconstructed along <110= direction in the boundary structure. Atomic models are constructed for these boundaries with the presence of non-tetracoordinated atoms. The stability of the boundary structure is explained by the π-like bonding between the nontetracoordinated atoms.

scholarly journals Elemental Mapping at Grain Boundaries in Alloy X-750 by EFTEM

1997 ◽  
Vol 3 (S2) ◽  
pp. 975-976 ◽  
Author(s):  
J. Bentley ◽  
N. D. Evans ◽  
E. A. Kenik
Keyword(s):  
Grain Boundary ◽  
Base Alloy ◽  
Boundary Migration ◽  
Analytical Electron Microscopy ◽  
Boundary Region ◽  
Heat Treatment Condition ◽  
Boundary Structure ◽  
Phase Identification ◽  
Elemental Mapping ◽  
Nickel Base

Alloy X-750 is a γ -strengthened, nickel-base alloy used in demanding high-temperature applications. The HTH commercial heat treatment condition provides excellent strength and good corrosion resistance. However, the resultant precipitate structure is complex with fine (˜20 nm) intragranular γ' phase and copious intergranular precipitation of at least four phases (γ', M23C6, M23B6, and TiN). The intergranular precipitation causes localized grain boundary migration and results in a convoluted grain boundary structure. Such complex grain boundary microstructures increase the difficulty of phase identification and interfacial composition measurements by traditional analytical electron microscopy methods. Elemental mapping by EFTEM is a useful additional or alternative technique for characterizing such structures. A Gatan Imaging Filter (GIF) on a Philips CM30 (LaB6) was used in the current investigation. Experimental details have been summarized elsewhere.Elemental maps of Cr, Ti, and Ni (net L23 intensities) are presented in Fig. la-c for a typical grain boundary region of a HTH heat treated specimen.

Atomic structure of undoped Σ=5 symmetrical-tilt grain boundary in strontium titanate

1993 ◽  
Vol 51 ◽  
pp. 986-987
Author(s):  
V. Ravikumar
Keyword(s):  
Grain Boundary ◽  
Strontium Titanate ◽  
Atomic Structure ◽  
Processing Parameters ◽  
Boundary Region ◽  
Boundary Structure ◽  
Reference Structure ◽  
Structure Changes ◽  
Symmetrical Tilt ◽  
Tilt Grain Boundary

Strontium titanate is an important electroceramic material which, under appropriate processing and dopant additions exhibits both varistor and Grain Boundary Layer Capacitor (GBLC) behavior. The presence of electrically active grain boundaries is essential for obtaining these properties. The first step towards correlating the grain boundary structure to properties is to determine the detailed atomic structure of the boundary, which includes its geometric structure, chemistry and electronic structure. We present here our TEM investigation of the atomic structure of an undoped (“pristine”) symmetrical tilt grain boundary in SrTiO3. This provides the basic reference structure, changes to which can be studied as a function of doping and/or processing parameters, and correlated to electrical and dielectric properties.Self-supported TEM samples were made from bicrystals of SrTiO3 through the conventional sample preparation route. Fig. 1 shows a high resolution electron micrograph (Hitachi H9000) of a representative grain boundary region in the sample.

Grain boundary structure intergranular fracture and the role of segregants as embrittling agents

1980 ◽  
Vol 295 (1413) ◽  
pp. 165-165 ◽  
Keyword(s):  
Grain Boundary ◽  
Intergranular Fracture ◽  
Boundary Region ◽  
Boundary Structure ◽  
Orientation Relation ◽  
Substantial Evidence ◽  
Grain Boundary Structure ◽  
Different Types

There is substantial evidence, from studies of annealed and crept aluminium, which indicates that once a dislocation has entered the boundary region between two grains it dissociates to form several grain boundary dislocations of Burgers vectors determined by the orientation relation between the grains. Subsequent behaviour depends on boundary structure, the dissociation products remaining bunched together in certain boundaries and moving apart in others, indicative of a friction type stress active in the boundary. A simple classification of the different types of boundary, where friction stresses were either high or low, into coincidence and non-coincidence boundaries, however, was not possible.

scholarly journals Effect of Grain Boundary Structure on Grain Boundary Diffusivities in the Au/Ag System

1990 ◽  
Vol 209 ◽  
Author(s):  
Qing Ma ◽  
R. W. Balluffi
Keyword(s):  
Thin Film ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Tilt Angle ◽  
Structural Unit ◽  
Boundary Structure ◽  
Grain Boundary Structure ◽  
Unit Model ◽  
Tilt Boundaries ◽  
Accumulation Method

ABSTRACTGrain boundary chemical diffusivities for a series of symmetric [001] tilt boundaries in the Au/Ag system were measured by the surface accumulation method using newly developed thin-film multi-crystal specimens, in which the grain boundaries feeding the accumulation surface were all of the same type. Possible effects due to segregation at the grain boundaries and surfaces were avoided. CSL boundaries of low-Σ ( i.e., 5, 13, 17, 25) and also more general boundaries with tilt angles between the low-Σ orientations were selected. The diffusivities were found to vary monotonically with tilt angle ( i.e., no cusps at low-Σ's were found) in a manner consistent with the Structural Unit model.

Computed Structures of [001] Symmetrical Tilt Boundaries in Covalently Bonded Materials

1985 ◽  
Vol 63 ◽  
Author(s):  
J. T. Wetzel ◽  
A. A. Levi ◽  
D. A. Smith
Keyword(s):  
Grain Boundary ◽  
Silicon Germanium ◽  
Computer Modelling ◽  
Field Potential ◽  
Boundary Structure ◽  
Bonded Materials ◽  
Grain Boundary Structure ◽  
Covalently Bonded ◽  
Tilt Boundaries ◽  
Symmetrical Tilt

ABSTRACTThe dependence of the structure of (210) and (310) symmetrical [001] tilt boundaries in silicon, germanium and diamond on the Keating covalent force field (potential) has been investigated by computer modelling. We have found that the sensitivity of grain boundary structure to variations of the Keating potential depends on the local atomic arrangement at the grain boundary.

Fundamental Effects of Boundary Structure on Nano-Scale Conductive Heat Transfer

2002 ◽  
Author(s):  
Nicole Aitcheson ◽  
Dan Fickes ◽  
John R. Lloyd
Keyword(s):  
Energy Transport ◽  
Bulk Material ◽  
Boundary Surface ◽  
Boundary Region ◽  
Phonon Transport ◽  
Boundary Structure ◽  
Conductive Heat ◽  
Low Dimensional ◽  
Boundary Characteristics ◽  
Structural Boundary

Modeling of energy transport in nanostructures is very different from that in larger scaled materials. Researchers have reported considerably lower “thermal conductivity” in nano-scaled materials compared to the corresponding bulk material property. This observation is most often attributed to phonon-boundary interactions. However, in-depth explanations of this phenomenon are lacking. This study defines the fundamentals of low-dimensional phonon transport by relating the structural boundary characteristics of a material with the mechanisms of phonon transport. The structural boundary of a material controls phonon transport, creating a “boundary region” rather than a boundary surface, resulting in apparent differences in energy transport efficiency between the bulk material and the nano thin materials.

The Role of Crystallization of an Intergranular Glassy Phase in Determining Grain Boundary Residual Stresses in Debased Aluminas

1989 ◽  
Vol 170 ◽  
Author(s):  
Nitin P. Padture ◽  
Helen M. Chan ◽  
Brian R. Lawn ◽  
Michael J. Readey
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Residual Stresses ◽  
Glassy Phase ◽  
Analytical Techniques ◽  
Ceramic Materials ◽  
Strength Test ◽  
Second Phase

AbstractThe influence of microstructure on the crack resistance (R-curve) behavior of a commercial debased alumina containing large amounts of glassy phase (28 vol %) has been studied using the Indentation-Strength test. The effect of two microstructural variables, viz. grain size and the nature of the intergranular second phase (glassy or crystalline) has been evaluated. Crystallization of the intergranular glass was carried out in order to generate residual stresses at the grain boundaries, which have been shown to enhance R-curve behavior in ceramic materials. Enhancement of the R-curve behavior was observed with the increase in grain size. However, no effect of the nature of the intergranular second phase on the R-curve behavior, in small and large grain materials, was observed. The results from characterization of these materials using various analytical techniques is presented, together with possible explanations for the observed effects.

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