Modulus Spectroscopy and Dielectric Dispersion Studies in Alkali Metal Perchlorates

Abstract

Alkali metal perchlorates (KCIO,, RbClO,, and CsCIO,) undergo a structural phase transition from the orthorhombic to the cubic phase at elevated temperatures. A detailed dielectric study of these crystals across the phase transition is carried out at different frequencies. The crystals are found to exhibit pronounced dielectric dispersion in the kHz frequency range. The results support the view that these transitions are of order-disorder type. The dielectric behaviour at temperatures above T, is discussed in terms of modulus spectroscopy. An estimate of conductivity relaxation times above the phase transition temperatures made from modulus spectroscopy data gives values of 3.1, 12.2 and 17.7 ps for KClO,, RbCIO,, and CsClO,, respectively. Alkalimetallperchlorate (KClO,, RbClO, und CsClO,) erleiden bei erhohten Temperaturen einen strukturellen Phaseniibergang von der rhombischen zur kubischen Phase. Eine ausfuhrlichere dielektrische Untersuchung dieser Kristalle uber den Phasenubergang wird bei verschiedenen Temperaturen durchgefuhrt. Es wird gefunden, daB die Kristalle eine ausgepragte dielektrische Dispersion im kHz-Bereich zeigen. Die Ergebnisse unterstutzen die Ansicht, da8 diese Ubergiinge vom Typ: Fehlordnung--0rdnung sind. Das dielektrische Verhalten bei Temperaturen oberhalb T, wird mit der Modulspektroskopie diskutiert. Eine Abschatzung der Leitfahigkeitsrelaxationszeiten oberhalb der Phaseniibergangstemperaturen aus den Modulspektroskopiewerten ergibt Werte von 3,l; 12,2 und 17,7 ps fur KCIO,, RbC10, bzw. CsC10,.

Dielectric and AC Conductivity οf Potassium Perchlorate, KCLO4

“…Further details are given elsewhere [2]. This is in good agreement with previous work [1,2]. The higher values of ε and/or ε in the transition temperature region may suggest the existence of Ferro electricity.…”

“…This transition is of the order -disorder type, i.e., it is due to the disorder of the ClO 4 group. Further details are given elsewhere [2]. This is in good agreement with previous work [1,2].…”

“…Thus, the possibility of a ferroelectric phase transition has been excluded in the present work since there is no evidence for the formation of hysteresis loops over the investigated temperature range. Thus the higher values of ε and ε is therefore due to the surface polarization effect [2] rather than Ferro electricity. One can summarize the phase transition as follows:…”

“…All these perchlorates are salts of perchloric acid which attract the attention of investigators owing to their interesting properties. For example, most of these compounds undergo structural phase transitions at high and low temperatures [1][2][3][4][5][6][7][8]. Furthermore the crystal structures of some members of these series were determined [9][10][11].…”

“…For the alkali metals perchlorate with M = Cs, Rb, and K, the modulus spectroscopy and dielectric dispersion were performed on single crystals prepared by the gel technique [2]. A high temperature phase transition was detected around ≈ 302…”