Ionic Conductivity and Thermal Stability of BiF3 Crystals

• Published in: Crystallography reports 2023-04, Vol.68 (2), p.297-301
• Main Authors: Sorokin, N. I., Karimov, D. N.
• Format: Article
• Language: English
• Subjects: Crystallization; Crystallography and Scattering Methods; Crystals; Enthalpy; Erbium; Ion currents; Ion transport; Physical Properties of Crystals; Physics; Physics and Astronomy; Pyrohydrolysis; Rare earth elements; Sublimation; Temperature dependence; Thermal stability; Yttrium
• ISSN: 1063-7745; 1562-689X
• DOI: 10.1134/S1063774523020189

The temperature dependence of the ionic conductivity σ dc ( T ) and thermal stability of BiF 3 crystals with the structure of orthorhombic β-YF 3 (sp. gr. Pnma , a = 6.5620(1) Å, b = 7.0144(1) Å, c = 4.8410(1) Å, V / Z = 55.71 Å 3 ), grown from melt by the vertical directional crystallization technique have been investigated. The electrical characteristics of BiF 3 are obtained from impedance measurements in the temperature range of 360−540 K. The σ dc value at T = 500 K and the ion transport activation enthalpy Δ H a are found to be 2.5 × 10 −5 S/cm and 0.48 ± 0.05 eV, respectively. The Δ H a value for the crystal studied is smaller by a factor of 1.4 in comparison with the isostructural rare-earth (Tb, Ho, Er, Y) trifluorides, which is due to the high electronic polarizability and large ionic radius of Bi 3+ cations. It was found that BiF 3 crystals are thermally stable at temperatures up to 550−600 K; at higher temperatures degradation was observed due to the sublimation and pyrohydrolysis of this material. The formation of oxofluoride phases is responsible for the detected conductivity jump in the dependence σ dc ( T ) at T ∼ 600 K.