The phase separation, into metallic and insulating regions, which occurred in this material at low dopant concentrations, was investigated by using electron paramagnetic resonance techniques. A paramagnetic center which could probe the phase separation process was found in ceramic and powdered specimens. The intensity of this resonance was shown to be directly related to the surface area of the specimen. This led to the conclusion that a paramagnetic Cu2+ center, situated at surfaces or grain boundaries, was present. An additional phase separation was proposed which occurred in regions which were near to those surfaces.

G.Wübbeler, O.F.Schirmer, S.Köhne: Physical Review B, 1996, 54[13], 9054-7