Dielectric relaxation of Ca⁺⁺–vacancy dipoles in KCl + KBr mixed crystals

Abstract

Using dielectric loss and ionic thernio-current (I.T.C.) techniques the dielectric relaxation of KC1 + KBr mixed crystals doped with Ca++ was measured. It was found that the activation energy, H , for dipole reorientation decreases as the Br-minority anion concentration increases in the KC1 + KBr:Ca++ mixed crystal. I n KBr $-KCl:Ca++ (C1as a minority anion) the activation energy for dipole reorientation increases as the C1-minority anion increases. In addition to the relaxation peak that displaces with the minority CIanion concentration, another one was found in KBr + KCl:Ca++, but not in the KCI -1 + KBr: Ca++ system where Br-is the minority anion. The experimental resultsareexplained, for minority anion concentration not higher than lo%, in terms of lattice parameter change and of the local effect of the minority anion. Die dielektrische Relaxation von Ca-+-dotierten KCl + KBr-Mischkristallen wurde mit dielektrischen Verlusten und Ionen-Thermostromen (I. T. C.) gemessen. Es wird gefunden, daO die Aktivierungsenergie der Dipol-Reorientierung H rnit wachsender Br-MinoritLtsanionenkonzentration in den KCI + KBr: Ca++-Misehkristallen abnimmt. I n KBr + + KCI : Ca+ + (C1-als Minoritatsanion) nimmt die Aktivierungsenergie der Dipol-Reorientierung mit der C1--MinoritLtsionenkonzentration zu. ZusLtzlich zu einem Relaxationsmaximum, das sich rnit der C1-Minoritatsanionenkonzentration verschiebt, wurde ein anderes in KBr + KCl:Ca++ gefunden; jedoch nicht im KCI -1-KBr:Ca++-System, woBrdas Minorititsanion ist. Fur Minoritatsanionenkonzentrationen von nicht hoher als 10% werden die experimentellen Ergebnisse mit der h d e r u n g der Gitterparameter und dem lokalen EinfluB des MinoritLtsanions erklart.

The H− Ion as a Diffusion Trap for Divalent Ions in KCl

“…The relaxation of the I.V. dipole was measiired using the dielectric loss and ionic thernio-current techniques as described in [9].…”

“…dipole relaxation was recently studied using dielectric loss and I.T.C. techniques [9]. The study of the interaction between the H-anion and the I.V.…”

Reorientation of Eu2+-cation vacancy dipolar complex in KCl/KBr binary crystals

“…[6,7] Like Eu 2+ , Ca 2+ doped KCl and KBr unitary single crystals exhibit a single peak in the depolarization curve. However, KCl 1−x Br x binary crystals have for both dopants a complex depolarization curve with a structure that depends principally on the composition x and not so much on the dopant [8,9]. In general the curves present two to three humps that at first glance may suggest the presence of several different dipoles.…”

“…This fact by itself may sug gest that each peak is composed out of several relaxation pro cesses. Indeed, it has been argued that for compositions with less than 10% of KCl, that resemble still the original KBr peak with only one accompanying second peak, the accompanying peak is composed out of at least three relaxation processes [9]. It is clear from the fore going that the interpretation of the ITC curve in the case of binary crystals is not as simple as in the case of unitary crystals and this may be the reason why the ITC technique, despite its successes in unitary crystals, has never been deployed as a tool for the investigation of the aggrega tion process in binary crystals.…”

“…However, in contrast to optical techniques, ITC could poten tially filter out the dipoles from small aggregates, and there fore could be a useful supplemental technique provided that the depolarization process itself is sufficiently understood to gain the necessary confidence in the interpretation of the results. An attempt to understand the depolarization process in binary crystals has been made in a previous study on ITC in Ca 2+ doped binary alkalihalide crystals [9], however, only for compositions with small concentrations of minority anions of typically lower than 10%. For these compositions, the ones close to KCl have an ITC curve showing a single depolariza tion peak, that is little affected by composition, whereas for the ones close to KBr, resemble a second peak emerging at the low temperature side of the main peak [8,9].…”