Investigation of Interaction between a Dislocation and a Br Ion in NaCl:Br Single Crystals

Abstract

Strain rate cycling tests were carried out under simultaneous Blaha effect measurement on NaCl single crystals doped with Br—. Curves of strain rate sensitivity (SRS) of flow stress versus stress decrement due to superimposition of oscillatory stress were obtained. The curves are stair-like and show two plateau regions at low and higher stress decrement, and a middle region where the SRS decreases with increasing stress decrement, as reported in a previous paper concerning KCl:Br—. The stress τp at the first bending point of the curve, which is considered to be the effective stress due to Br—, decreases with increasing temperature and becomes zero at a critical temperature Tc = 270 K. The difference SRSp between the SRS at the first and second plateau regions decreases with temperature in contrast to the case of KCl:Br—. This means that the force–distance profile of the interaction between a dislocation and a Br— ion for NaCl:Br— is different from that for KCl:Br— and is pointed near the top. It is found that the interaction energy between a dislocation and a Br— impurity for NaCl:Br— crystal is 0.37 eV.