VACANCIES AND DISLOCATIONS IN EUROPIUM DOPED KCL SINGLE CRYSTALS

The influence of europium dopant on the defect structure of KCl single crystals was studied. KCl crystals were grown by the Bridgeman-Stockbarger method with various amounts of europium trichloride added. The europium concentration, determined by a spectro-photometric method, was increased in seven steps from 1·1 × 10-5 to 1·65 × 10-4 mole ratio. Optical absorption curves were recorded and their analysis indicated that they consisted of peaks characteristic of bivalent europium only. With the aid of these curves the molar absorption coefficient of Eu in KCl was computed. Ionic conductivity measurements were made to detect the variation of positive ion vacancy concentration. Dislocation density was determined both from etch pit counts and X-ray rocking curves. It was found that the change of the parameters followed the change of the europium concentration. The increase of ionic conductivity with increasing europium concentration supported the finding of the optical absorption measurements, i.e. the optically effective dopant ions are bivalent. It also suggested that they are substitutional and probably introduce an equal number of positive ion vacancies. The correspondence of dislocation density to the europium concentration is best understood in terms of the interaction between impurities and moving dislocations. Due to the thermal shrinkage of the crystals stresses were introduced which deformed the single crystals. In those which were hardened by more substitutional europium ions the plastic deformation was associated with more dislocations than in those with lesser substitutional europium content. Based on similar works, a suggestion is made as to the possible interaction mechanism between the substitutional europium ions and moving dislocations. © 1968.