HALL-EFFECT OF THE HIGH-TC SUPERCONDUCTORS Y-BA-CU-O AND GD-BA-CU-O

We report Hall-effect measurements in the slowly cooled and quenched states of ABa//2Cu//3O//7// minus // delta , A equals Y, Gd. The slowly cooled sample is superconducting at T equals 90K. The Hall constant (R//H) is of the order of 10** minus **9m**3/C, corresponding to approximately 1 hole per unit cell at 300K. Unusually for metals, R//H increases on decreasing temperature. Quenched from 750 degree C to room temperature, the sample is semiconductor at least down to 4. 2K. R//H is increased approximately 20 times with respect to the slowly cooled sample, with activated temperature dependence.