Effects of Y substitution and oxygen deficiency on the superconducting transitions in YxGd1-xBa2Cu3O7-δ

A series of ceramic samples of Y(x)Gdl(1-x)Ba(2)Cu(3)O(7-delta) with various Y substitution x and oxygen deficiency delta is prepared and investigated with scanning electron microprobe, X-ray diffraction (XRD) and electrical resistivity. The normal resistivity is almost independent of Y substitution except for the x = 0.3 sample which indicated poor crystallinity. Although oxygen deficiency results in higher normal resistivity and lower superconducting transition temperature T-c, higher T-c is achieved in the Y-substituted sample. XRD analyses show that the increase in the crystal c-axis due to oxygen deficiency is suppressed by the Y substitution. The origin of improved T-c is discussed in relation to the suppression of the c-axis stretching and the suppression of decrease in the hole concentration in the CuO2 plane. (C) 2002 Elsevier Science B.V. All rights reserved.