The self-trapped electron center in this material (a Pb23+ molecular ion which resulted from the trapping of a conduction electron by a pair of Pb2+ lattice cations along the a-axis) exhibited a strong temperature dependence of both the g and hyperfine tensor values of the electron spin resonance spectrum at temperatures of between 10 and 78K. This unusually large variation, which was not observed in the case of the iso-electronic Tl2+ and Pb23+ impurity centers of alkali chlorides, appeared to be related to the anisotropic thermal expansion of the layered PbCl2 lattice.

S.V.Nistor, E.Goovaerts, D.Schoemaker: Physical Review B, 1995, 52[1], 12-5