Anisotropy of Ionic Conductivity of TbF₃ Crystals

Temperature measurements (in the range of 375–830 K) of the ionic conductivity of terbium trifluoride single crystals (structure type β-YF₃) along three unit-cell crystallographic axes (a, b, and c) have been performed. It is found that TbF₃ crystals (orthorhombic system, sp. gr. Pnma) have a weak anisotropy of electrical conductivity: σ_||b/σ_||a = σ_||b/σ_||c ≈ 2. The conductivity along the b axis is σ_||b = 8 × 10^–6 S/cm at 500 K. The anisotropy of fluorine-ion conductivity in rare-earth fluorides with β-YF₃, LaF₃ (tysonite), and β-BaTm₂F₈ structures is discussed in the contest of the specific features of their atomic structure.