Ionic conduction and crystal structure of β-Pb1−xSnxF2 (x≤0.3)
Abstract The crystal structures of β-Pb 0.9 Sn 0.1 F 2 (Sn10) and β-Pb 0.8 Sn 0.2 F 2 (Sn20) were determined using single crystal intensity data on a four-circle diffractometer. The structures have cubic symmetry; the lattice parameters: a =5.946(1) A, V =210.2(2) A 3 , space group Fm3m (No. 225) for Sn10 and a =5.957(1) A, V =211.4(1) A 3 , space group Fm3m (No. 225) for Sn20. The structures were refined to w R =4.2% for Sn10 and 3.6% for Sn20 by the least-squares method, using 76 unique reflections with | F 0 |>3 σ (| F 0 |). The fluorine ions are statistically distributed in 32 sites of (0.25+ δ , 0.25+ δ , 0.25+ δ ). δ , displacement from the normal fluorine site, increases with the SnF 2 content. The isotropic temperature factor of the fluorine, B iso =16.5(2.3) A 2 , for Sn20, is very large compared with that for Sn10 ( B iso =3.18(45) A 2 ). Ionic conductivity in this system increases with the magnitude of the temperature factor of the fluoride ion.