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Determination of the velocity of mobile dislocations by nuclear spin relaxation measurements
Author(s) -
Hackelöer H. J.,
Selbach H.,
Kanert O.,
Sleeswyk A. W.,
Hut G.
Publication year - 1977
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2220800127
Subject(s) - materials science , relaxation (psychology) , spin (aerodynamics) , nuclear magnetic resonance , condensed matter physics , physics , psychology , thermodynamics , social psychology
Wolf's general theory of rotating‐frame nuclear spin‐lattice relaxation is applied to the effect caused by dislocations moving at an average velocity v . Equations are presented for the dependence of the NMR relaxation rate R (ϱ) Don the mean waiting time τ of a dislocation before an obstacle, valid in both the weak‐and the strong‐collision regions. In the latter the Slichter‐Ailion‐Rowland‐Fradin theory applies. Nuclear spin relaxation tests on 23 NaCl and 23 NaF single crystals deformed at constant strain rates ϵ confirm the theory. The experimental data for the predicted maximum in R (Q) D(reached only for NaCl at ϵ m = 20 s ―1 ) yield directly τ m = 2.8 × 10 ―5 s, the mobile fraction of dislocations Q m /Q t = 0.26. The value of ϵ m , together with the mean distance between obstacles of ≈ 2 × 10 ―4 cm, derived from the slope of the curve in the strong‐collision region, leads to v m = 7.1 cm s ―1 , corresponding to a mobile dislocation density ϱ m = 1.4 × 10 8 cm −2 .