Correlation between hole concentration and T-c in (La2-xYx)Ba-2(CayCu4+y)O-z superconductors

The structural and superconducting properties of series of (La-2-Y-x(x))Ba- 2(CayCu4 + y)O-z (La-2125); 0.0 < x < 0.5,0.0 < y < 1.0, compounds having t etragonal triple perovskite structure and maximum T-c, of 78 K for x = 0.4 (y = 2x, are investigated using X-ray diffraction, susceptibility, resistiv ity and oxygen content measurements. It is observed that, both oxygen conte nt and hole concentration (p) increase as the samples are doped with higher concentration of Ca2+ and T-c, increases with increasing y = 2x as p incre ases upto an optimum level of 0.349 at x = 0.4. Thus by adding equal amount s of CaO and CuO alongwith Y3+ for La3+ in La2Ba2Cu4Ox (La-224) semiconduct or, superconductivity occurs. The addition of Ca is turning on a mechanism a which affects both hole concentration and T-c, in a closely related way t o that of YBa2CU3O7-delta (Y-123). (C) 1999 Elsevier Science B.V. All right s reserved.