THERMAL-BOUNDARY BETWEEN NORMAL CONDUCTIVITY AND FLUCTUATION SUPERCONDUCTIVITY IN YBA2CU3O7-DELTA

The absence of a linear behaviour of the dependence of the resistance R(T) over a temperature interval 77-300 K was observed for ceramic sup erconductors YBa2CU3O7-delta and thick polycrystalline films of the sa me composition with the addition of silver. A comparative analysis of the excess conductivity for HTSC and metal samples, characterizing the deviation R(T) from a linear dependence, allows one to determine the onset temperature of fluctuation superconductivity: within 105-110 K. The analysis of fluctuation superconductivity is performed using the A slamazov-Larkin model. A smooth transition from the one-dimensional to the two-and three-dimensional nature of superconducting fluctuations in the order parameter was observed for ceramic samples as the tempera ture decreased. (C) 1998 Academic Press Limited.