An Investigation of the Point Defect Scattering of Phonons by Minute Concentrations of Cr4+ in Corundum by Thermal Techniques

It is necessary to improve the resolution, brightness and signal-to-noise ratio(s/n) for the detection and identification of point defects in crystals. In order to observe point defects, multi-beam dark-field imaging is one of the useful methods. Though this method can improve resolution and brightness compared with dark-field imaging by diffuse scattering, the problem of s/n still exists. In order to improve the exposure time due to the low intensity of the dark-field image and the low resolution, we discuss in this paper the bright-field high-resolution image and the corresponding subtracted image with reference to a changing noise level, and examine the possibility for in-situ observation, identification and detection of the movement of a point defect produced in the early stage of damage process by high energy electron bombardment.The high-resolution image contrast of a silicon single crystal in the [10] orientation containing a triple divacancy cluster is calculated using the Cowley-Moodie dynamical theory and for a changing gaussian noise level. This divacancy model was deduced from experimental results obtained by electron spin resonance. The calculation condition was for the lMeV Berkeley ARM operated at 800KeV.

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Point Defect Absorption and Dislocation Loop Formation at Grain Boundaries in Hvem-Irradiated Zr and Its Alloys:1. Influence of Solute Addition

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010011862x ◽

1985 ◽

Vol 43 ◽

pp. 350-351

Author(s):

R.A. Herring ◽

M. Griffiths ◽

M.H Loretto ◽

R.E. Smallman

Keyword(s):

Grain Boundary ◽

Grain Boundaries ◽

Point Defect ◽

Reactor Core ◽

Solute Concentration ◽

Nuclear Industry ◽

Dislocation Loops ◽

Loop Formation ◽

Component Material ◽

Impurity Interaction

Because Zr is used in the nuclear industry to sheath fuel and as structural component material within the reactor core, it is important to understand Zr's point defect properties. In the present work point defect-impurity interaction has been assessed by measuring the influence of grain boundaries on the width of the zone denuded of dislocation loops in a series of irradiated Zr alloys. Electropolished Zr and its alloys have been irradiated using an AEI EM7 HVEM at 1 MeV, ∼675 K and ∼10-6 torr vacuum pressure. During some HVEM irradiations it has been seen that there is a difference in the loop nucleation and growth behaviour adjacent to the grain boundary as compared with the mid-grain region. The width of the region influenced by the presence of the grain boundary should be a function of the irradiation temperature, dose rate, solute concentration and crystallographic orientation.

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On the interpretation of dislocation-loop growth during in-situ high-voltage Electron Microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010017579x ◽

1990 ◽

Vol 48 (4) ◽

pp. 532-533

Author(s):

E. Holzäpfel ◽

F. Phillipp ◽

M. Wilkens

Keyword(s):

Point Defect ◽

Rate Equations ◽

Rate Theory ◽

Dislocation Loops ◽

High Voltage Electron Microscopy ◽

Vacancy Migration ◽

Voltage Electron ◽

Reaction Rate Theory ◽

Defect Reactions

During in-situ radiation damage experiments aiming on the investigation of vacancy-migration properties interstitial-type dislocation loops are used as probes monitoring the development of the point defect concentrations. The temperature dependence of the loop-growth rate v is analyzed in terms of reaction-rate theory yielding information on the vacancy migration enthalpy. The relation between v and the point-defect production rate P provides a critical test of such a treatment since it is sensitive to the defect reactions which are dominant. If mutual recombination of vacancies and interstitials is the dominant reaction, vαP0.5 holds. If, however, annihilation of the defects at unsaturable sinks determines the concentrations, a linear relationship vαP is expected.Detailed studies in pure bcc-metals yielded vαPx with 0.7≾×≾1.0 showing that besides recombination of vacancies and interstitials annihilation at sinks plays an important role in the concentration development which has properly to be incorporated into the rate equations.

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