The technique of thermally stimulated depolarization currents was exploited to search dipolar defects in NaCl crystals doped with divalent nickel in a wide concentration range. The results were critically compared with those typical of other impurities. It has been shown that the main features of the detected polarizations are qualitatively similar to those characteristic of alkali halides doped with divalent cations. The differences observed in some instances can be understood in terms of different mobility and/or stability of the elementary defects related with the impurities.
A correlated set of experiments was performed with a view to study the effect of trivalent bismuth upon some properties of NaCl, KCI and RbCI crystals. For NaCI the effect of BiO^{+} ions was also investigated. It was stated that: 1. The hydrolytic properties of bismuth are responsible for the formation of BiO^{+} centres also in crystals doped with BP^{3+} ions. 2. During all experiments performed, the dopant remains in the form of trivalent cations. 3. Optical absorption spectra of bismuth are similar to those characteristic of other heavy metal ions with the s^{2} electronic configuration. 4. The charge excess of BP^{3+} ions is compensated by cation vacancies whereas for BiO^{+} ions the preferential bonding between Bi^{3+} and O^{2-} serves for the charge compensation.
On the basis of ITC studies, complemented by some spectroscopic and ionic conductivity measurements, it was stated that dielectric relaxations of the NaCl:Cr^{3+} crystals are more complicated than those typical of AH:Me^{2+} systems. The complexity of these phenomena concerns the number, shape and positions of the bands appearing in the ITC spectrum. The origin of the main peaks was discussed in terms of relaxations related with the chromium centres; substitutionally and off-center located Cr3^{+} ions, accompanied by two cation vacancies at geometrically different positions, and Cr clusters distributed around dislocations were considered.
JavaScript is turned off in your web browser. Turn it on to take full advantage of this site, then refresh the page.