EFFECT OF FE SUBSTITUTION ON THE THERMAL-EXPANSION OF THE HIGH T(C) SUPERCONDUCTOR Y1BA2CU3OY

Thermal expansion measurements have been carried out on Fe substituted superconducting compounds YBa2(Cu1-xFex)3Oy (0 < x < 4%) using a high resolution dilatometer employing the three terminal capacitance techn ique. The experimental set up is sensitive enough to detect changes in alpha of less than 10(-8) K-1. Results show that the jump DELTAalpha in the coefficient of linear thermal expansion at the superconducting transition temperature, T(c), increases almost linearly with Fe concen tration. The normal state thermal expansion coefficient alpha first de creases, attains a minimum value around x = 1% and then increases for higher Fe concentrations. The oxygen content per unit formula is almos t constant up to x = 1% and then increases rapidly with x. It has also been observed that the anomalous behaviour of alpha around 260 K obse rved by Meingast et al [22] for Fe concentration x = 5% is due to inad equate annealing of the sample.