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As a common effect of a large and variable temperature gradient and a temperature pulse, a thermal instability of a new type has been observed in high- T c superconductors. The primary effect is the temporal change of local energy density, that causes a dynamic state of simultaneously coexisting normal and superconducting domains, establishing a spatial and temporal variation of superconducting and normal states. The fluctuation of the ratio of the superconducting and normal volume fractions can be detected by the oscillation of DC and AC voltages measured on the samples. Supposing that every jump of the AC voltage represents the transformation of a single coherent domain, it leads to the average value of the linear dimension of domains as 2.1 mm, characteristic time of the transformation as 7.5 s and velocity of the propagation of this effect as 0.3 mm/s in the case of Y 1 Ba 2 Cu 3 O 7−δ specimens. The macroscopic consequence of the thermal disturbance introduced into the sample is the appearance of a giant flux creep. Its existence is confirmed by comparison of our measurements to others, by analytical and numerical calculations of the forces acting on the vortices and by evaluation of the effect of the huge fluctuation created in the samples by our experiments.

Using the thermal scanning susceptometry, completed with the thermal pulse method, a series of hills has been observed on the susceptibility (real component) curves of Y-based ceramic superconductors. Supposing that these are the manifestations of cooperative vortices (superconducting domains promoted by the granular and defect structure of the material), the medium coherence length (ξ VG ~ 2 mm), medium correlation time (τ ~ 51.2 s), a dynamic ( z ~ 5.7) and a static ( v ~ 1.1) scaling exponents have been determined. Because the determined exponents of the instability are very similar to those predicted theoretically and verified experimentally for vortex-glass structures, we suggest that the observed fluctuations are produced by vortex-glass-like domains.

It is shown by electrical modelling that the appearance and type of the resistivity or conductivity peak depends only on the character (or role) of the energy source used during the normal-superconducting or superconducting-normal transition. Treating the substituting circuit as series resistors (source of constant voltage) or parallel conductors (source of constant current), the response function has a maximum in time (and accordingly by the temperature) giving the possibility for the appearance of a resistivity or conductivity peak in both the case of cooling and heating. It is also demonstrated that the existence of the spatial distribution of local inhomogeneities in the sample is equivalent to the non-uniform temporal distribution of the transition.

Irradiation effects of low-dose (10 14 n/cm 2 ) neutrons on the resistance and AC susceptibility of multiphase YBa 2 Cu 3 O 7 and Tl 2 Ca 1 Ba 2 Cu 2 O 8 have been studied. Experimental results show that dispersed local superconducting regions in the samples may be unified to form a continuous percolating network using neutron irradiation. If the concentration of oxygen vacancies and interstitials is below or above an optimum value, the irradiation increases or decreases, respectively, the superconductive volume fraction and - via Cu-O bond length - the T c value.

Effect of the change of temperature on single-phase ceramic superconducting Y1Ba2Cu3O7−x samples has been investigated. The cooling down and heating up cycles represent a thermo-mechanical corrosion during which hair-crackings and breakings can come into being. The thermal expansion experiments result in linear and non-linear dilatation curves depending on the character of cooling and heating. The water corrosion manifests itself in fine secondary Ba(OH)2 and BaCO3 microcrystals developing on the surfaces of basis microcrystals which form the samples.

A high-T c ceramic superconducting magnet of cylindrical shape was constructed of rings, made of an Y 1 Ba 2 Cu 3 O 7−x compound. The magnet consisting of 20 individual rings can produce a magnetic field of 0.02 T (exactly 207 Oe) at a superconducting current of 65 A. To avoid the problems of the Joule-heating on the resistivity of ohmic contacts, the magnet was supplied magnetically by a contactless, inductive method. In this way, the magnetic field is limited only by the superconducting parameters of the material.