QUASI-2D BEHAVIOR OF HTSCS - THE CONSEQUENCE OF THE SMALL EFFECTIVE THICKNESS OF SUPERCONDUCTING LAYERS

New evidence of quasi-two-dimensional (2D) behaviour in granular bulk high-T-c samples is presented. Anomalously large differences between t he mean-field critical temperature and the temperature of the Berezins ky-Kosterlitz-Thouless-like transition is found to be in good agreemen t with calculations based on the small inherent thickness of CuO2 laye rs. Two successive mechanisms, quasiparticle and Josephson tunnelling, are used to explain the experimental data obtained on a large set of samples ranging from one unit cell to perfect single crystals. A simpl e phenomenological analysis based on the renormalization of 2D superfl uid density of charge carriers through the thickness-restrictive mecha nism of their mean free path is developed.