The temperature dependences of the resistivity of granular high-temperature superconductor YBa_2Cu_3O_7–δ ρ( T ) are measured at various transverse external magnetic fields 0 ≤ H _ext ≤ 100 Oe in the temperature range from the resistivity onset temperature T _ρ = 0 to the superconducting transition critical temperature T _ c at the transport current density from 50 to 2000 mA/cm^2. The effect of the external magnetic field and transport current density on the kinetics of phase transitions in both subsystems of granular two-level HTSC ( T = T _ c 2J, T _ c 1g, T _ c ) is determined. The feasibility of the topological phase transition, i.e., the Berezinsky–Kosterlitz–Thouless transition, in the Josephson medium at T _ c 2J < T _BKT < T _ c 1g “in transport current” is established, and its feasibility conditions are studied.

The problem of establishing the correlation between, on the one hand, the chemical and phase compositions of Ni_1– x W_ x alloys (0 ≤ x ≤ 0.5) and, on the other hand, the character of the temperature dependences of the electrical resistivity, is considered. Based on the experimental ρ( T ) curves, the concentration dependences of are reconstructed in the wide temperature range (50 K ≤ T ≤ 273 K). The ρ( x ) curves have features related to a change in the crystal structures of the alloys (concentration fcc–bcc phase transition), their magnetic structures and percolation processes occurring in the two-phase fcc + bcc medium.