The tetragonal material was prepared by solid-state reaction and was characterized by means of X-ray Rietveld analysis, differential scanning calorimetry, differential thermal analysis and alternating-current conductivity measurements. The room-temperature tetragonal phase was composed of a cationic framework that was made up of layers which were perpendicular to the c-axis, and which followed the sequence: PbPbSnSn. The conductivity versus temperature curves, at temperatures of between 170 and 573K, exhibited a gradual change in slope; from a region of high activation energy (30kJ/mol) to one of low activation energy (10kJ/mol) near to room temperature. This behavior was not associated with any lattice symmetry change, and corresponded to a so-called diffuse phase transition.

R.Kanno, S.Nakamura, K.Ohno, Y.Kawamoto: Materials Research Bulletin, 1991, 26[11], 1111-7