scholarly journals Cooperative chemical rebonding in the segregation of impurities in silicon grain boundaries

1996 ◽  
Author(s):  
A. Maiti ◽  
M.F. Chisholm ◽  
S.J. Pennycook ◽  
S.T. Pantelides
Keyword(s):  
Grain Boundaries ◽  
Segregation Of Impurities

Segregation of Impurities at Grain Boundaries and Other Compositional Inhomogeneities in Chill-Casted Silicon Ingots

1982 ◽  
pp. 874-882 ◽  
Author(s):  
S. Pizzini ◽  
L. Braicovich° ◽  
L. Calliari ◽  
M. Gasparini ◽  
C. M. Mari ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Segregation Of Impurities

The “Solidification” of Grain Boundaries with Increasing Temperature

1994 ◽  
Vol 357 ◽  
Author(s):  
Witold Lojkowski ◽  
Bogdan Palosz
Keyword(s):  
Solid State ◽  
Melting Point ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
High Temperatures ◽  
Low Temperatures ◽  
Melting Behavior ◽  
Wetting Transitions ◽  
Increasing Temperature ◽  
Segregation Of Impurities

AbstractThe aim of the paper is to explain the recently observed de-wetting grain boundary transition with increasing temperature. On the example of a bicrystal from the Fe-6at.%Si alloy, it was found recently that as temperature is increased, the following GB transitions take place: “solid” (or regular) GB-→“premelted” GB →“solid” GB. At the same time the wetting/de-wetting transitions have taken place. Another example of such GB behavior was discovered during sintering of alumina. The inverse melting behavior is explained as follows: low melting point impurities cause GB premelting at low temperatures, However de-segregation of impurities at high temperatures causes return of the GB structure to its regular “solid” state.

Analysis of the Defect Chemistry at Gd-Doped Ceria Grain Boundaries

2001 ◽  
Vol 7 (S2) ◽  
pp. 1184-1185
Author(s):  
Y. Ito ◽  
Y. Lei ◽  
N.D. Browning ◽  
T.J. Mazanec
Keyword(s):  
Grain Boundaries ◽  
Defect Chemistry ◽  
Contrast Imaging ◽  
Ceramic Electrolyte ◽  
Oxygen Coordination ◽  
Probe Size ◽  
Z Contrast ◽  
Electron Energy Loss ◽  
Total Ionic Conductivity ◽  
Segregation Of Impurities

Gd3+ doped Ce oxides are very promising candidates as electrolytes for solid oxide fuel cells operating at ∼ 500 °C. For their successful commercial implementation, a full understanding of the defect chemistry in the bulk and at grain boundaries is essential. in particular, the contribution of the grain boundaries to the total ionic conductivity through such effects as the segregation of impurities, dopants and vacancies is of crucial importance. Here the effect of the atomic structure on the local electronic properties, i.e. oxygen coordination and cation valence at grain boundaries of the fluorite structured Gd0.2Ce0.8O2-x ceramic electrolyte is investigated by a combination of Z-contrast imaging and electron energy loss spectroscopy (EELS) in the JEOL 201 OF STEM (operating at 200keV, and aligned for a probe size ∼ 0.2 nm).Preliminary O K- and Ce M45-edges were acquired from points in the grains (A and B) and grain boundary shown in Figure 1.

Effects of Impurities And Alloying Elements on Iron Grain Boundary Cohesion

1997 ◽  
Vol 475 ◽  
Author(s):  
D.E. Ellis ◽  
X. Chen ◽  
G.B. Olson
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Physical And Mechanical Properties ◽  
Alloying Elements ◽  
Metallic Materials ◽  
Crucial Importance ◽  
Intergranular Embrittlement ◽  
Long Time ◽  
Impurity Doped ◽  
Segregation Of Impurities

In metallic materials, where grain boundaries(GB) are of crucial importance, impurities and alloying elements play an important role in determining their physical and mechanical properties because the behavior of a grain boundary may change drastically with the presence of impurities and alloying elements. For example, in iron and its alloys, including industrially important steels, the intergranular embrittlement is usually associated with segregation of impurities, like P and S, toward the GBs. On the other hand, alloying elements, like Mo and Pd, are helpful for intergranular cohesion in iron, due to either direct cohesion effect or effect upon embrittling potency of other impurities. Understanding the mechanisms of impurity-promoted embrittlement and the consequent cohesion(decohesion) effects is becoming more and more important and remains as a challenge for materials scientists. There have been intensive investigations on these mechanisms for a long time and with the progress in computing techniques in recent years, calculations on more realistic representations of impurity-doped grain boundaries have become possible[1–4].

STEM Investigation of Segregation and Local Structure at Grain Boundary in Tetragonal Zirconia

1997 ◽  
Vol 3 (S2) ◽  
pp. 549-550
Author(s):  
H. Gu ◽  
F. Wakai
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Solid Electrolytes ◽  
Tetragonal Zirconia ◽  
Boundary Structure ◽  
Contrast Imaging ◽  
Amorphous Films ◽  
Grain Boundary Structure ◽  
Z Contrast ◽  
Segregation Of Impurities

Y or Ca stabilized tetragonal ZrO2 (TZP) exhibits superplasticity at high temperature, and can also be used as solid electrolytes. Those properties are dictated by structure and chemistry of grain boundaries, which can be controlled by segregation of impurities or additives. The grain boundaries were found either covered by amorphous films or free of the film. Co-segragation of additives and stabilizers has also been observed. To fully understand the correlation between segregation and grain boundary structure, a dedicated STEM (VG HB601) capable of EDX/EELS analysis and phase/Z-contrast imaging is employed to study 3Y-TZP doped with 0.3 and 0.9 mol% SiO2.Although Y-L lines arc dominated by overlapping Zr-L lines in EDX, Y excess at grain boundaries can still be measured by “spatial difference” which removes Zr signal with a spectrum from the bulk. The co-segregation of Si and Y is also observed (Fig. 1) at many boundaries. Their average excesses arc 5±2 nm−2and 25±10 run−2 respectively, close to 1 monolayer each of SiO2 and Y2O3.

Investigations of the Bonding Changes Associated with Grain Boundary Embrittlement

1996 ◽  
Vol 458 ◽  
Author(s):  
V. J. Keast ◽  
J. Bruley ◽  
D. B. Williams
Keyword(s):  
Electronic Structure ◽  
Grain Boundary ◽  
Energy Loss ◽  
Grain Boundaries ◽  
Edge Structure ◽  
Grain Boundary Embrittlement ◽  
Impurity Elements ◽  
Electron Energy Loss ◽  
Segregation Of Impurities ◽  
Boundary Embrittlement

ABSTRACTThe embrittlement of materials through the segregation of impurities to the grain boundaries is a common and industrially important problem. Despite considerable investigation, the mechanism by which the impurity elements cause embrittlement is not well understood. A change in the electron energy loss near edge structure (ELNES) has been observed at Cu grain boundaries containing Bi. This result provides experimental evidence that a change in the electronic structure at the grain boundary is responsible for embritdement.

scholarly journals Cooperative Chemical Rebonding In The Segregation Of Impurities In Silicon Grain Boundaries

1996 ◽  
Vol 442 ◽  
Author(s):  
A. Maiti ◽  
M. F. Chisholm ◽  
S. J. Pennycook ◽  
S. T. Pantelides
Keyword(s):  
Grain Boundary ◽  
Ab Initio ◽  
Grain Boundaries ◽  
Structural Transformation ◽  
Atomic Resolution ◽  
Segregation Energy ◽  
Site Variation ◽  
Segregation Of Impurities

AbstractWith ab initio calculations we show that the experimentally observed large segregation energies of As at Si grain boundaries can be explained by the formation of isolated dimers or ordered chains of dimers of threefold-coordinated As along the cores of grain boundary dislocations. We also find the intriguing possibility that As segregation may drive structural transformation of certain grain boundaries. Recently we have obtained the first atomic-resolution STEM images of As in a Si grain boundary, consistent with the formation of As dimers. Segregation energy of As dimers was found to be significantly higher in isolated dislocation cores, where larger site-variation in strain than in grain boundaries lead to further lowering of the electronic levels of As deep into the bandgap.

Calculations of Cu L2,3 fine structure at grain boundaries

1996 ◽  
Vol 54 ◽  
pp. 528-529
Author(s):  
P. Rez ◽  
J.M. Maclaren
Keyword(s):  
Mechanical Properties ◽  
Fine Structure ◽  
Energy Loss ◽  
Grain Boundaries ◽  
Recent Work ◽  
Electronic States ◽  
White Line ◽  
Small Probe ◽  
Metal Atoms ◽  
Segregation Of Impurities

The segregation of impurities to grain boundaries in metals and alloys has been known for some time to make changes in ductility. Examples of this effect are the embrittlement of copper by the addition of bismuth and the ductilization of Ni3Al by boron impurities. The mechanism by which these dramatic changes in mechanical properties arise is still largely unknown. It has been suggested that embrittling elements draw charge from neighbouring metal atoms while impurities that enhance ductilty act in the opposite way. Changes in the electronic states can be detected as changes in the energy loss spectrum when a small probe in a FEG STEM is moved across the boundary. Recent work by Muller has shown significant differences between the Ni L3 spectrum from grain boundaries in Ni3Al with and without boron. Bruley has shown that a “white line”, indicative of empty Cu d states, appears in the Cu L3 edge from Cu atoms near boundaries where bismuth has segregated.

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