Effect of the temperature and pressure on the transport properties of the superconducting ceramic BaPb1−<i>x</i>Bi<i>x</i>O3

The temperature and pressure dependences of the critical current, the current-voltage characteristics, and the conductivity of samples of the ceramic BaPb1−xBixO3 (BPB), obtained under different technological conditions, are investigated for purposes of studying the barrier characteristics of the intergrain boundaries of granulated metal-oxide superconductors with the structure of perovskite in the formation of the transport properties. It is found that the Josephson and single-particle tunneling effects depend strongly on the resistivity of the samples, determining the strength of the intergrain coupling. In the strong-coupling limit synchronization encompasses the entire current-conducting chain of the percolation network of the sample. Increasing the resistance of the material destroys the synchronization of the links and gives rise to an increasing influence of proximity effects in the IVC and in the dependence Ic(T), while in the weak coupling limit it gives rise to reentrant phenomena in the dependences Ic(T) and R(T). In the state of single-particle tunneling the characteristic features of the quasiparticle density of states are reflected in the IVC. On the basis of the results obtained it is concluded that the surface layers of the granules make the determining contribution to the resistance of the sample and two principal conduction mechanisms, on whose ratio the observed effects depend, are pointed out: tunneling through the Schottky barrier and hopping along localized impurity states. The pressure increases the potential of the Schottky barrier and causes the surface (usually amorphous) layer of the BPB granules to become metallized.

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