In-Situ NMR Investigation of Dynamical Behavior of Point and Line Defects During Deformation of NaCl
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IN-SITU NMR INVESTIGATION OF DYNAMICAL BEHAVIOR OF POINT AND LINE DEFECTS DURING DEFORMATION OF NaCI
K. DETEMPLE, 0. KANERT, K.LINGA MURTY* AND J.TH.M. DEHoSSON** University of Dortmund, Postfach 500 500, 46 Dortmund 50, FRG *North Carolina State University, Raleigh NC 27695-7909
"**University of Groningen,
The Netherlands
ABSTRACT Spin lattice relaxation time in the rotating frame [Tip is investigated in pure NaCl
single crystals as a function of temperature in-situ during deformation. Transition from 2phonon Raman process to atomic diffusion was noted at around 500K in the undeformed material and the activation energy was determined to be that for the diffusion of extrinsic vacancies. Enhanced spin relaxation rates were noted during constant strain-rate deformation at temperatures from ambient to about 750K. These enhancements were identified to arise from dislocation motion at lower temperatures while enhanced diffusion due to excess vacancies at higher temperatures. This excess concentration increased with increased strain-rate and in-situ annealing of deforma-tion induced excess vacancies is noted at high temperatures. INTRODUCTION Dynamical properties of various defects in solids have been investigated by a large variety of experimental techniques and nuclear spin resonance methods have been used extensively to investigate the diffusion of point defects in solids at high temperatures, localized motion of atomic defects in solids at low temperatures and very recently the motion of line defects [dislocations] in solids during deformation.' NMR has been recognized as one of the most powerful techniques for diffusion studies in solids and has been extensively used to investigate various diffusion parameters such as the activation energies for diffusion in both nonmetals and metals. These techniques were extended by Murty and Ruoff2 to examine the superimposed hydrostatic pressure and to determine the activation volumes for motion and formation of Schottky defect pairs.The advantage of these techniques over the conventional tracer diffusion, for example, is that one can obtain a better microscopic picture of the diffusional process since NMR probes the rate of atomic jumps rather directly. Later advances leading to the evaluation of spin-lattice relaxation times in rotating frame resulted in extreme sensitivity of this parameter to atomic jump processes and extensions of these techniques were made by Rowland and Fradin, 3 Kanert and othersl in evaluating the impurity diffusion in alloys. These techniques, in addition, made it possible to probe the jumping dislocations in-situ during deformation in a non-interactive fashion. 1 .4 We utilize these methodologies in the present investigation to evaluate the super-imposed effects of deformation on spin-lattice relaxation time in the rotating frame [Tip] in single crystalline NaC1 at temperatures from ambient to about 900K at various constant strain-rates. We identified strain-enhanced diffusion at high temperatures and dislocation contribution at low temperatures.
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