It is shown that after plastic deformation a decrease of the ionic conductivity appears in the structure sensitive region of Ca‐doped KCl and NaCl crystals near RT. The decrease depends on the strain and Ca content and is related to a reduction of the concentration of free cation vacancies. For OH‐ and O2‐doped NaCl crystals an increase was found. It is possible to anneal the conductivity decrease with discrete activation energies. To explain the conductivity change two mechanisms are proposed, being simultaneously effective in the crystal: the interaction between vacancies and charged dislocations (mechanism I) and the condensation of vacancies in vacancy clusters (mechanism II). Mechanism I is preferentially effective for pure crystals, mechanism II for Ca doped crystals.

B y conductivity measurements of Ca doped KCI crystals between 20 and 90 "C i t is shown that the conductivity isotherms may be described by the association theory only for small Ca concentrations below 6 x 10-j mole fraction Ca/KCl. The effect of the OH ions is given here in terms of characteristic deviations. For higher Ca concentrations the shape of the conductivity isotherms depends on the history of the crystals. By investigations of crystals with suitable thermal pretreatment it is shown that the shape of the isotherms, and especially the slow temporal decrease of the conductivity of quenched specimens, may be explained hj-precipitation processes of the Ca ions.A4n Nessnngen der Leitfahigkeit Ca-dotierter KC1-Kristalle zwischen 20 und 90 "C wird gezeigt, daB sich niir im Bereich kleiner Ca-Konzentrationen bis zu etwa 6 x Molanteilen Ca/KCl die Leitftihigkeitsisothermen gemtiR der Assoziationstheorie beschreibcn lassen. Durch OH-Ionen bedingte Abweichungen machen sich hier in charakteristischer LVeise bemerkbar. Bei groRercn Ca-Gehalten hangt der Verlauf der Leitfkhigkeitsisothermen von der Vorgewhichte der Kristalle ab. An thermisch geeignet vorbehandelten Proben konntc dabei gezeigt werden, daR der Verlauf der Isothermen und speziell die langsame zeitliche Abnahme der Leitfahigkeit abgeschrecktcr Proben durch Ausscheidungsprozesse der Ca-Ionen erklart werden kann.

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Untersuchungen zum Gyulai-Hartly-EffektEs werden Ergebnisse von Experimenten zum Nachweis einer moglichen Zunahme der elektrischen Leitfahigkeit wahrend der plastischen Deformation von reinen und Ca-dotierten NaCl-, KC1-und KBr-Kristallen beschrieben. Die Deformation erfolgte durch einaxiale Kompression und im Scherungsversuch. Es konnte gezeigt werden, daB das fur die Leitfiihigkeit reprbentative elektrische Signal stets durch Polarisationserscheinungen infolge elektrisch geladener Versetzungen uberlagert ist. Eine Leitftihigkeitserhohung wiihrend Deformation konnte im Rahmen der MeBgenauig keit in keinem Fall nachgewiesen werden.Results of experiments are reported concerning a possible enhancement of the dc conductivity during plastic deformation of pure and Ca doped NaCl, KCl and KBr crystals. The deformation was performed by uniaxial compression and by shearing. It could be shown that the electrical signal representing the conductivity always is superimposed by a polarization phenomenon due to electrically charged dislocations. In the limits of the measurement accuracy i t was impossible in all cases to find an enhancement of the conductivity during deformation.

In an earlier paper (1) the low-temperature conductivity of Ca doped KCI single crystals was investigated by means of conductivity isotherms within the temperature range at 60 OC. In the case of higher Ca concentrations deviations from the shape