THERMOPOWER OF ION-IRRADIATED YBA2CU3O7-DELTA-FILMS

Experimental data of the temperature dependence of the thermoelectric power S(T) for differently doped HTSC-samples recently found renewed i nterest in the context of the van Hove scenario as well as the spin ga p behavior. Furthermore, a universal relation between S(290K) and the hole concentration p has been reported. On the other hand, ion irradia tion of HTSC- films with ions of medium energy (typically 350 keV) is known to produce defects leading to a strong increase in normal-state resistivity and a depression of the superconducting transition tempera ture T-c. The idea of the present work is to combine both techniques t o test whether the ion-induced defects are predominantly oxygen vacanc ies within the CuO-chains, reducing p as monitored by S(290K). For thi s purpose, c-axis oriented YBa2Cu3O7-films on (1OO)-SrTiO3 substrates were irradiated with 350 keV He+-ions. After each irradiation step an XRD analysis and an S(T)-measurement for T-c < T < 295K is performed. A is shown that for small fluences the ion-induced S(T)-changes can be attributed to oxygen displacements destroying the CyO-chains, while f or higher fluences additional defects within the CuO2-planes have to b e taken into account. The corresponding S(T) behavior is comparable to what has been reported for Zn-substituted underdoped HTSC-samples.