Thermal depolarization in crystals of CaF₂:Na⁺, SrF₂:Na⁺, and BaF₂:K⁺

Abstract

The defect complexes formed when the univalent metal ions Na+ or K+ are incorporated in CaF2, SrF2, or BaF2 have been investigated by the technique of thermal depolarization. Only a single depolarization event is found in CaF2:Na+ and SrF2:Na+ and this is ascribed to nearest neighbour Nas+Fv− complexes (s = substitutional ion, v = vacancy). Evidence for this kind of complex is also observed in BaF2:K+ and a second depolarization peak at 138 K in these crystals is attributed to an M+ impurity.

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

“…The reported energy E d for the dipole orientation or disorientation ranges from 0.47 to 0.53 eV [2][3][4] and is larger than our experimental value of 0.45 eV for low sodium concentration. The difference in E d may be due to our ITC measurement procedures or apparatus, but the details are unclear.…”

“…The peak temperatures (T dm ) observed by Shelley and Miller [2] and Ong and Jacobs [4] were about 162 and 167 K, respectively. The latter T dm by Ong and Jacobs is slightly higher than ours.…”

“…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.…”

Simulations of some simple localised defects in alkali-doped alkaline-earth fluorides

“…Table 10 displays the calculated 'reorientation' energies AU, of the [I(A)*S(A)] pair (linear motion, rotation) and [V(F)*S(A)] pair (rotation). The bottom of the table is devoted to the activation energies deduced from analyses [5,6,10,24] of the ITC and DR experiments. Our Li and Na values agree fairly well with those calculated by Jacobs and co-workers [lo], but the heavy (K or Rb) [I(A)*S(A)] pairs-perhaps [V(F)*S(A)] too-are somewhat questionable, because of the probably poor reliability of the SRI.…”