Mechanical synthesis and structural properties of the fast fluoride-ion conductor PbSnF4.

A fluoride-ion conductor, γ -PbSnF 4 , was synthesized by the mechanical milling. In addition, β -PbSnF 4 was obtained by aging the γ -PbSnF 4 at 473 K. The electrical conductivity of β -PbSnF 4 is relatively higher than that of γ -PbSnF 4 at 298 K. The crystal structure analysis of γ - and β -PbSnF 4 was carried out using neutron diffraction data. From the obtained occupancies, fluoride ions were located at the F γ (1) normal site (62%) and F γ (2) interstitial site (38%) in γ -PbSnF 4 and the F β (1) normal site (31%), F β (2) normal site (25%), and F β (3) interstitial site (44%) in β -PbSnF 4 . In particular, the number of fluoride ions at the F interstitial site increased after the γ -to- β phase transition: 38% at F γ (2) to 44% at F β (3). It is most likely that the ratio of fluoride ions to vacancies (or the effective carrier concentration) was optimized in the “–F β (1)–F β (3)–F β (3)–F β (1)–” conduction pathways of fluoride ions in β -PbSnF 4 . [ABSTRACT FROM AUTHOR]