Synthesis, structural characterization and fluctuation conductivity of HoBa2Cu3O7−δ–SrTiO3 composites

Single-phase polycrystalline samples of HoBa2Cu3O7−δ superconductor and SrTiO3 isolator were produced by means of the solid state reaction technique. After structural characterization of both materials, superconductor-isolator composites were produced with nominal isolator volume percentages between 0% and 10%. Resistivity measurements for the composites and the HoBa2Cu3O7−δ sample with different currents evidenced a superconducting transition with critical temperature TC=92K, with wider transitions with increasing either isolator content or measurement current. Fluctuation conductivity analyses were carried out to obtain the exponents characterizing the conductivity divergence. Above TC, apart from the typical Gaussian and critical fluctuations an atypical regime with critical exponent about 0.14 is observed as a precursor of the transition. Below TC, it is observed that the coherence transition characteristic exponent increases rapidly with increasing isolator percentage in the composites and does not show important changes when modifying the current in the pure superconductor sample.