EFFECT OF CO SUBSTITUTION ON THE THERMAL-EXPANSION OF THE HIGH-T-C SUPERCONDUCTOR Y1BA2CU3OY

Measurement of the coefficient of linear thermal expansion, alpha, has been carried out for the high-T-c superconducting compounds Y1Ba2(Cu1 -xCox)(3)O-y using a high resolution capacitance dilatometer in the te mperature range 77-300 K. The studies reveal that the superconducting and normal state values of alpha, increase almost linearly with increa se in Co content. All the superconducting samples exhibit the expected second order phase transition (from normal to superconducting state) characterized by discontinuity in alpha, at their respective transitio n temperatures, T-c. The jump Delta alpha, is also found to increase a lmost linearly with the increase in Co concentration. There is evidenc e that the temperature dependence of alpha for compounds having large Co concentration (greater than or equal to 3%) depends on the conditio ns of specimen growth.