Effect of Fe substitution on the thermal expansion of the high Tc superconductor Y1Ba2Cu3Oy

Thermal expansion measurements have been carried out on Fe substituted superconducting compounds Y1Ba2(Cusub(1-x)Fex)3Oy (0<x<4%) using a high resolution dilatometer employing the three terminal capacitance technique. The experimental set up is sensitive enough to detect changes in α of less than 10-8K-1. Results show that the jump Δα in the coefficient of linear thermal expansion at the superconducting transition temperature, Tc increases almost linearly with Fe concentration. The normal state thermal expansion coefficient α first decreases, attains a minimum value around x = 1% and then increases for higher Fe concentrations. The oxygen content per unit formula is almost constant up to x = 1% and then increases rapidly with x. It has also been observed that the anomalous behaviour of α around 260K observed by Meingast et al (1991) for Fe concentration x = 5% is due to inadequate annealing of the sample. (author). 29 refs., 5 figs., 1 tab