THE EFFECT OF PRESSURE AND SILVER IMPURITY ON THE SUPERCONDUCTING PROPERTIES OF THE HTS YBA2CU4O8

The effect of uniform compression is studied on the superconducting tr ansition temperature of the HTS ceramics YBa2(Cu1-xAgx)(4)O8+/-delta(x =0, 0.05, 0.1, 0.15). It is shown that the pressure effect in these co mpounds differs considerably from that in the system YBa2(Cu1-xAgx)(3) O7-delta. The observed peculiarities are discussed on the basis of the van Hove anomaly in the electron energy spectrum of oxide cuprates. T he correspondence of the superconducting properties of the 1-2-4 and 1 -2-3 systems under pressure with certain models of high-temperature su perconductivity is discussed. The nature of nonlinearity of the temper ature dependence of the electrical resistance of the 1-2-4 system in t he normal state and the effect of substitution of silver for copper on it are studied. The corresponding phase diagram is constructed. The c orrespondence of the observed increase in crossover temperature with t he Nagaoza-Lee theory is discussed. (C) 1997 American Institute of Phy sics.