THE DIFFERENCE OF DOPING EFFECTS BETWEEN YBa2Cu3-xCoxOy AND YBa2Cu3-xZnxOy

The measurements of X-ray diffraction, d.c. resistance versus temperature and Hall coefficients at low temperature have been performed for YBa2Cu3-xMxOy systems. (x = 0.00, 0.025,0.05,0.075,0.10,0.125,0.15,0.20,0.25,0.275,0.30,0.325,0.35,0.375,0.40 for M = Co; x=0.025,0.05,0.075,0.10,0.15,0.20,0.30 for M = Zn)The crystallographic data show that an orthorhombic-tetragonal phase transition takes place as Co content increases,while the crystal structure exhibit drastic changes with Zn content. The measurement of resistances indicates that a metal-semiconductor transition occurs at certain x for Co dopant hut not found for Zn dopant. The hole carrier concentration raduces with Co content monotoneous-iy but varies nonmonotoneously with Zn content, giving a maximum at about x= 0.15 The concepts of localization and acceptor are used to explain these phenomena. The suppression of Tc for both systems is discussed with various possible suppression mechanisms.