DEFECT CHEMISTRY AND ANISOTROPIC TRANSPORT IN YBA2CU3O6 ... 7

Special preparation procedures and analytical techniques allows us to prepare chemically and crystallographically well defined YBa2Cu3O6...7. The analyses reveal the possibility of disorder in the Y- and Ba-sublattice in addition to defects in the O-sublattice. Attempts are made to explain the O2 partial pressure dependence of the electronic conductivity using simple defect models. In particular, a considerable hole trapping is suggested. The anisotropy of the electronic conductivity is found to be significantly large. Careful electrochemical polarisation experiments (ac, dc) with glass-sealed specimen allow the determination of the ionic conductivity and of the chemical diffusion in the same experiment. The chemical diffusion coefficient is also obtained using conductivity relaxation results. The diffusion analysis, which also takes into account the electron-ion interaction according to the theory of "conservative ensembles" strongly suggests a large ionic anisotropy. Preliminary measurements (chemical relaxation) confirm the anisotropy of D̃. © 1990.