Ionic transport and defect structure of vitreous beryllium fluoride

Vitreous BeF₂ was prepared by two techniques; (1) remelting of a technical grade material, and (2) vacuum distillation/fluoridation. Infrared spectroscopy studies have established that the first material contains about 0.5 wt.% hydroxyl, predicted to be coherently incorporated into the vitreous network as edge-linked Be(OH)₄]^2? units. The distilled BeF₂ is water-free. The dc electrical conductivity of the remelted BeF₂ was measured as σ = (7.9 × 10³/T) exp(?24500 cal/mol/RT) ω^?1 cm^?1 and for the distilled BeF₂ as σ = (3.0 × 10⁵/T) exp(?36700 cal/mol/RT ω^?1 cm^?1 at temperatures to 280°C. Ionic transport studies utilizing a dc electrolysis polarization technique with N₂?F₂ and H₂?HF gas electrodes have demonstrated that the fluorine ion is the transport species. A general model for fluorine transport is proposed based upon a modified anti-Frenkel defect model. The difference in the fluorine transport process for the undistilled grade of BeF₂ is seen as a consequence of the anti-Frenkel defect pair interaction with the Be(OH)₄^2? groupings.