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Spins, Phonons, and Hardness

Published online by Cambridge University Press:  10 February 2011

John J. Gilman
John J. Gilman*
Affiliation:
Department of Materials Science and Engineering, University of California at Los Angeles, Los Angeles, California 90024
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Abstract

In crystals (and/or glasses) with localized sp3 or spd-bonding orbitals, dislocations have very low mobilities, making the crystals very hard. Classical Peierls-Nabarro theory does not account for the low mobility. The breaking of spin-pair bonds which creates internal free-radicals must be considered. Therefore, a theory based on quantum mechanics has been proposed (Science, 261, 1436 (1993)). It has been applied successfully to diamond, Si, Ge, SiC, and with a modification to TiC and WC. It has recently been extended to account for the temperature independence of the hardness of silicon at low temperatures together with strong softening at temperatures above the Debye temperature. It is quantitatively consistent with the behaviors of the Group IV elements (C, Si, Ge, Sn) when their Debye temperatures are used as normalizing factors; and appears to be consistent with data for TiC if an Einstein temperature for carbon is used. Since the Debye temperature marks the approximate point at which phonons of atomic wavelengths become excited (as contrasted with collective acoustic waves), this confirms the idea that the process which limits dislocation mobility is localized to atomic dimensions (sharp kinks).

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 410: Symposium S – Covalent Ceramics III-Science and Technology of Non-Oxides , 1995 , 199
Copyright
Copyright © Materials Research Society 1996

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References

REFERENCES

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