UNUSUAL TRANSPORT AND MAGNETIC-PROPERTIES OF TB-DOPED YBA2CU3O7 SINGLE-CRYSTALS AND EPITAXIAL THIN-FILMS

The electrical resistivity rho(T) and magnetic susceptibility chi(T,H) (1.8 less-than-or-equal-to T less-than-or-equal-to 350 K and 0 less-than-or-equal-to H less-than-or-equal-to 5.5 T) have been measured on single crystals and epitaxial thin films of Y1-xTbxBa2Cu3O7. The T(c) is 92 K and irrespective of Th doping up to x=0.50. For T>T(c), rho(T) has a linear dependence, i.e., rho(T)almost-equal-to A+BT, with the reduced resistivity rho(T)/rho(250 K) for x=0.10, 0.25, and 0.50, being independent of Th doping. The results of magnetic susceptibility along with the computation of effective moment of Th in the presence of crystal electric fields (CEF) tend to suggest that the Tb is mixed valent. The insensitivity of T(c) to the Tb doping and the possibility that Tb may be mixed valent are in sharp contrast to the case of Pr and Ce doping which have been shown to be very deleterious to superconductivity. The magnetic susceptibility chi(T) is extremely anisotropic, and this anisotropy cannot be explained by simple models with CEF effects.