Thermal expansion of orthorhombic and tetragonal phases of the high T _c superconductors RE₁Ba₂Cu₃O _y (RE=Y, Gd, Dy)

Measurements of the coefficient of linear thermal expansion α have been carried out for the orthorhombic and tetragonal phases of RE₁Ba₂Cu₃O _y (RE=Y, Gd, Dy) compounds using a high resolution capacitance dilatometer in the temperature range 77-300 K. All the superconducting samples exhibit a jump Δα at their respective transition temperatures, T _c. Evidences of, sample-to-sample variation in α values and dependence of Δα on the sample preparation conditions, have been obtained. The non-superconducting samples, in general, exhibit lower values of α possibly because of lowering of oxygen content.