PRESSURE EFFECT ON T-C FOR (YB1-XPRX)BA2CU3O7

The pressure effects on the superconducting transition temperature (dT (c)/dP) have been systematically measured for a series of (Yb1-xPrx)Ba 2Cu3O7-delta with x ranging from 0 to 0.3. It has been found that dT(c )/dP<0 for x=0, 0.2, and 0.3, and dT(c)/dP>0 for x=0.05, 0.075, 0.1, a nd 0.15. We have unexpectedly observed a pressure-induced increase in the normal state resistivity for x=0.2 and 0.3, suggesting a decrease of the carrier concentration under pressure. Making use of the concept of pressure-induced charge transfer incorporated in the model of hole depletion by Pr doping, we have proposed a phenomenological model, wh ich has successfully explained the x dependences of dT(c)/dP and T-c.