DEPENDENCE OF EU-O DISTANCE ON CE CONCENTRATION IN T' PHASE EU2-XCEXCUO4 DEDUCED FROM EU-151 MOSSBAUER ISOMER-SHIFT

The variation of the average Eu-O distance, d(Eu-O) with Ce doping is obtained from the Eu-151 Mossbauer isomer shift and discussed combinin g with that of the lattice constant, c, in T-phase Eu2-xCexCuO4. Becau se of the strong interaction of Ce4+ and O, the average Eu-O distance increases in contrast with shrinking in the lattice constant. Two stag es are observed in the d(Eu-O)-c relation. The differential coefficien t (d d(Eu-O)/d c) is -0.67 at the initial stage of Ce-doping (large c) and -0.17 at the second stage (small, c). The superconductivity appea rs when Ce is added over the turn point of the initial stage and the s econd stage.