Published online by Cambridge University Press: 16 February 2011
When a minor amount of HF is added to the SnF2 reacted with lead nitrate in aqueous solutions to prepare PbSnF4, a phase transition from tetragonal α-PbSnF4 to orthorhombíc o-PbSnF4 takes place. The transition is essentially bidimensional and takes place in the (a,b) plane of the unit-cell. The compactness of the structure increases at the transition. No essential structural change occurs: the transition is most likely displacive and it is driven by bidimensional nonuniform strain acting along the aand baxes of the unit-cell. This transition is similar to ferroic transitions (in this case, paraelastic → ferroelastic). No detectable change of chemical composition occurs at the transition, and the reason why the presence of HF in the reaction mixture causes the transition remains unknown.