INFLUENCE OF OIII ORDERING ON T-C IN YBCO

The results of systematic and comparative investigations, carried out by electron diffraction and resistivity measurements on oxygen-chain-e qualized polycrystalline YBCO samples in the existence domain of the o f the OIII structure, are reported. Experimental evidence for a charac teristic T-c of the OIII structure at about 75 K is provided. The resu lts, which evidence a crucial role of the structural order in determin ing T-c, were expected from the theoretical point of view but were nev er obtained previously. They show that, in the existence domain of the OIII structure, the degree of structural order results the most impor tant factor in determining T-c, since it determines the real efficienc y of the oxygen content in determining the hole carrier density in the CuO2 layers.