The influence of Mn doping on the thermal expansion of the high T _C superconductor YBa₂(Cu_1-xMn_x) ₃O_y

Measurement of the linear thermal expansion α has been carried out for Mn substituted YBa₂(Cu_1-xMn_x) ₃O_y (0≤x≤2%) using a high resolution dilatometer over the temperature range 10-300 K. Across the superconducting transition, the jump in the coefficient of linear thermal expansion Δα was found to decrease with increasing Mn content. For the pure sample, we observed a negative jump. While a threefold decrease in Δα with x ≤ 0.5% was observed, only slight changes in the oxygen content and transition temperature have been noted, as a function of the Mn concentration. The above observations clearly suggest that the substituent Mn is being incorporated into the superconductors as a whole and not in the form of a local cluster. Further, from the Ehrenfest relations, the pressure dependence of T_C (dT _C/dP) and the discontinuity in the compressibility, ΔK, are expected to decrease with the Mn concentration.