HALL-EFFECT IN Y2BA4CU7OX CERAMICS WITH 14.1-LESS-THAN X LESS-THAN-15.1

We have measured resistivity and Hall effect on polycrystalline samples of Y2Ba4Cu7O(x) with different oxygen concentrations. For x = 15.09 +/- 0.04 the Hall coefficient R(H) is + (0.6 +/- 0.2) x 10(-10) m3/C above 120 K and slightly increases near T(c). Such a small value of R(H) is close to what is found in YBa2Cu4O8, yet it is much smaller than in YBa2Cu2O7 and most of the other superconducting oxides. We interpret such a small R(H) value as a multiband effect related to the presence of CuO chains. As the oxygen content decreases, R(H) and the resistivity at room temperature rho (300 K) increase and simultaneously the superconducting transition temperature T(c) decreases. Nevertheless, we found that the sample with the lowest oxygen concentration, i.e., x = 14.13, is still metallic and superconducting with T(c) = 37 K. Moreover, the slope of the rho-vs-T curve increases with the decrease of the oxygen content. These features suggest that in Y2Ba4Cu7O(x) the removed oxygen modifies only a fraction of the free carriers, an effect which is probably associated to the single CuO chain structure.