Ionic thermocurrent investigations of CdF2

Abstract

When heated at a rate of 2 deg/min CdF2‐crystals doped with Na+, Ag+, and Li+ exhibit peaks of the ionic thermocurrents (ITC) at 103.5, 93 and 85.5 K, owing to the reorientation of monovalent cation‐fluorine vacancy dipoles (DO‐signals). In addition, comparatively larger ITC‐peaks due to the redisplacement of free fluorine vacancies (CD‐signals) are found between 180 and 220 K on the same crystals and on undoped ones. In the case of CdF2‐cyrstals doped with La3+, In3+, and Gd3+ redisplacement signals are observed between 300 and 350 K corresponding to the lower conductivity of these samples, whereas DO‐signals due to a reorientation of trivalent cation‐fluorine interstitial dipoles could not be detected in the whole range between 20 K and the temperature of the redisplacement signals. A comparison is made with ITC results on CaF2.

Equivalent electric circuit analyses of ionic thermocurrent in sodium-doped CaF2 crystals

“…2. T HTm for low N nom is also in good agreement with the value of 288 K reported by Kunze and Muller [3].…”

“…The ITC band at 162 K in a CaF 2 :Na crystal was first observed by Kunze and Muller [3] and was assigned to Na C -V F dipoles. The peak temperatures (T dm ) observed by Shelley and Miller [2] and Ong and Jacobs [4] were about 162 and 167 K, respectively.…”

“…Shelley and Miller [2] first studied the dynamics of Na C -V F dipoles in polycrystaline CaF 2 doped with NaF and derived the reorientation energy of 0.52 eV by varying the NaF concentration. Kunze and Muller [3] observed high-temperature ionic thermocurrent (HT ITC) in sodium-doped CaF 2 and CdF 2 crystals. After Ong and Jacobs [4] studied the dipole orientation in CaF 2 :Na, SrF 2 :Na and BaF 2 :K, a few ITC studies on sodium-doped CaF 2 crystals have been reported particularly on the dependence of HT ITC characteristics on sodium impurity concentrations.…”

Discharge of ions and space charge formation in CdF2 crystals with different kinds of electrodes

“…-There exist two kinds of peaks in CdF2 which are attributed to a spacecharge formation. One first order kinetics peak with a maximum position between 140 [6] and 210 K [6,7] depending on the impurity concentration and an extremely broad peak which is observed depending on the polarization temperature between 250 and 300 K [8,91. In table I1 the specific magnitudes Q/(S. Vp) for L = constant of these peaks are given for different arrangements of the electrodes.…”

POINT DEFECT INTERACTIONS IN CaF2 : GdF3

“…A relaxation in the dielectric spectrum that has been studied using the ionic therrnocurrent (ITC) technique (Bucci and Fieschi, 1964) by several groups (Royce and Mascarenhas, 1970 ;Stott and Crawford, 1971aand 1971b: Stiefbold and Huggins, 1972Kunze andMiiller, 1972 : Wagner andMascarenhas, 1972) was shown by Franklin and Marzullo (1970) to correspond closely in relaxation parameters to the relaxation giving rise to lifetime broadening (Watkins, 1959) of the pair EPR spectrum. This spectrum in turn has been firmly tied by ENDOR measurements (Baker, Davies and Hurrell, 196% and 1968b) to the pair formed by the substitutional trivalent cation and a nearest-neighbor interstitial fluorine.…”