Tetragonal and orthorhombic samples were characterized by using X-ray diffractometry, differential scanning calorimetry, differential thermal analysis, infra-red spectroscopy and impedance methods. It was found that the transport properties of the tetragonal and orthorhombic materials were very similar. The conductivity versus temperature plots, for temperatures ranging from 25 to 200C, exhibited a gradual change in slope in going from a region of high activation energy (55 or 35kcal/mol) to one of lower activation energy (8kcal/mol) at about 80C. During cooling, the conductivity was linearly dependent upon temperature, with an activation energy of 30kcal/mol. There was no symmetry change at the temperature where the conductivity curves exhibited a gradual change in slope.

G.Denes, G.Milova, M.C.Madamba, M.Perfiliev: Solid State Ionics, 1996, 86-88[1], 77-82