Hardening of Eu-doped KBr single crystals

Abstract

Abstract The yield stress of Eu-doped KBr crystals has been measured as a function of the testing temperature and impurity concentration after several types of heat treatment, in order to obtain various aggregation states of the impurity which are characterized by means of optical emission bands and ESR spectra of Eu2+ The hardening arising from free dipoles, small aggregates and precipitates has also been studied. For free dipoles, the hardening is temperature-dependent in the range 77-200 K and insensitive to the testing temperature above 200 K. The first stage is associated with an interaction between dipoles and edge dislocations whereas, in the second stage, the Snoeck mechanism operates. The formation of small aggregates does not alter the temperature-dependence and concentration-dependence of hardening. In contrast to the NaCl: Eu system, two temperature ranges of precipitation are found in Eu-doped KBr samples. If the annealing temperature is less than 200°C, a precipitated phase forms, whic...