Influence of aggregation-precipitation state of Eu²⁺ on the hardening behaviour of NaCl single crystals

Abstract

A study of the changes in the hardening of europium doped NaCl under dissolution and precipitation of solid solutions is reported. In order to have additional information on the change in the state of the impurity in the crystals, electron paramagnetic resonance, optical absorption and luminescence measurements were performed in parallel with the mechanical ones. The flow stress of the freshly quenched samples is linear in the Eu concentration up to ∼300 p.p.m. This result may suggest that the Eu²⁺ cation-vacancy dipoles are oriented at long range by the moving dislocations as described by the Snoek effect. The strengthening effect induced by metastable and stable precipitated phases of Eu²⁺ in this host crystal is also presented.