Ca effect on the normal-state and superconducting properties of Y-based HTS

We present the results on the normal-state (the resistivity, rho, thermopow er, S, and Hall coefficient, R) and superconducting properties of high-T-c compounds of the Y-123 family doped by calcium. We have studied single-dope d Y1-xCaxBa2Cu3Oy with different oxygen content, double-substituted Y1-xCax Ba1.5La0.5Cu3Oy and Y1-xCaxBa2Cu3-zCozOy (z = 0.25, 0.4), as well as co-dop ed Y1-xCaxBa2-xLaxCu3Oy and Y1-xCaxBa2Cu3-xCoxOy. Such a complex study allo wed us to reveal the general features of the Ca effect in Y-123. The result s on the normal-state transport properties have been analyzed in the framew ork of a narrow-band model assuming the existence of a sharp peak of the de nsity-of-states near the Fermi level. Within this model we were able to des cribe all the rho (T), S(T), and R(T) dependences, and to determine the par ameters characterizing the charge-carrier system in the normal state. Analy zing the doping influence on the T-c value, transport coefficients' behavio r, and the band structure parameters we have shown that all the specific fe atures of the Ca effect can be explained within an assumption on the introd ucing of additional Ca-induced states into the band responsible for the nor mal-state and superconducting properties of Y-123.