Ionic conductivity of ScF3 single crystals (ReO3 type) |
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Authors: | N. I. Sorokin D. N. Karimov V. V. Grebenev B. P. Sobolev |
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Abstract: | Electrical conductivity σ of ScF3 single crystals (sp. gr. (Pmoverline 3 m), ReO3 structure type) has been studied by impedance spectroscopy and compared with the electrical conductivity of rare earth HoF3 (β-YF3 type) and LaF3 (tysonite type) trifluorides. ScF3 crystals obtained by Bridgman directional solidification have ionic conductivity σ = 4 × 10–8 S/cm at 673 K. It is smaller than the σ values for LaF3 (sp. gr. (Poverline 3 c1)) and HoF3 (sp. gr. Pnma) single crystals by a factor of 104–105. The low conductivity of ScF3 crystals is due to the weak coordinating ability (coordination number CN = 6) and low electronic polarizability (αcat = 1.1 Å3) of Sc3+ ions. Mobile VF+ vacancies and less mobile interstitial Vi- ions (defects are formed according to the Frenkel mechanism) are involved in the ion transport. HoF3 and LaF3 single crystals have a high coordinating ability (CN = 9 for Ho3+ and CN = 11 for La3+) and a high electronic polarizability of cations (αcat = 1.6–1.9 Å3 for Ho3+ and αcat = 2.2 Å3 for La3+). Only mobile VF+ vacancies (defects are formed according to the Schottky mechanism) are involved in ion transport. |
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