The Ba–La–Cu–O system exhibits potential for high-temperature superconductivity. Metallic, oxygen-deficient compounds with the composition BaₓLa₅₋ₓCu₅O₅(3−y) were synthesized. Samples with x=1 and 0.75, annealed below 900°C under reducing conditions, consist of three phases, including a perovskite-like mixed-valent copper compound. Upon cooling, resistivity decreases linearly, then increases logarithmically, indicating localization onset. An abrupt resistivity drop by three orders of magnitude occurs, suggesting percolative superconductivity. The highest onset temperature is around 30 K, reduced by high current densities. This may result from percolative nature or 2D superconducting fluctuations in double perovskite layers. High-temperature superconductivity in the Li–Ti–O system was reported with Tc=13.7 K. Other oxides, like perovskites, exhibit superconductivity despite low carrier concentrations. In Nb-doped SrTiO₃, Tc=0.7 K due to strong electron-phonon coupling. Superconductivity in BaPb₁₋ₓBiₓO₃ also shows high Tc. The highest Tc in oxygen-deficient mixed crystals is 13 K with low carrier concentration. Flat bands and a strong breathing mode near 100 cm⁻¹, proportional to Tc, suggest higher Tc in perovskite-type oxides with enhanced electron-phonon coupling. Strong electron-phonon interactions in oxides occur via polaron formation or mixed-valent systems. A superconductivity to bipolaronic transition phase diagram was proposed. Jahn-Teller effect causes polaron formation. SrFe(VI)O₃ is a distorted perovskite insulator, while LaNi(III)O₃ is a Jahn-Teller undistorted metal. Mixed perovskites may exhibit Jahn-Teller-type polaron formation at metal-insulator transition. The Ba–La–Cu–O system has oxygen-deficient phases with mixed-valent copper, expected to have strong electron-phonon coupling and metallic conductivity. Samples were prepared via coprecipitation from aqueous solutions. X-ray analysis revealed three phases, including a layer-type perovskite-like phase. The third phase is thermally stable up to 1000°C. Conductivity measurements showed metallic behavior at high temperatures, with a sharp resistivity drop at lower temperatures, influenced by current density and annealing conditions.The Ba–La–Cu–O system exhibits potential for high-temperature superconductivity. Metallic, oxygen-deficient compounds with the composition BaₓLa₅₋ₓCu₅O₅(3−y) were synthesized. Samples with x=1 and 0.75, annealed below 900°C under reducing conditions, consist of three phases, including a perovskite-like mixed-valent copper compound. Upon cooling, resistivity decreases linearly, then increases logarithmically, indicating localization onset. An abrupt resistivity drop by three orders of magnitude occurs, suggesting percolative superconductivity. The highest onset temperature is around 30 K, reduced by high current densities. This may result from percolative nature or 2D superconducting fluctuations in double perovskite layers. High-temperature superconductivity in the Li–Ti–O system was reported with Tc=13.7 K. Other oxides, like perovskites, exhibit superconductivity despite low carrier concentrations. In Nb-doped SrTiO₃, Tc=0.7 K due to strong electron-phonon coupling. Superconductivity in BaPb₁₋ₓBiₓO₃ also shows high Tc. The highest Tc in oxygen-deficient mixed crystals is 13 K with low carrier concentration. Flat bands and a strong breathing mode near 100 cm⁻¹, proportional to Tc, suggest higher Tc in perovskite-type oxides with enhanced electron-phonon coupling. Strong electron-phonon interactions in oxides occur via polaron formation or mixed-valent systems. A superconductivity to bipolaronic transition phase diagram was proposed. Jahn-Teller effect causes polaron formation. SrFe(VI)O₃ is a distorted perovskite insulator, while LaNi(III)O₃ is a Jahn-Teller undistorted metal. Mixed perovskites may exhibit Jahn-Teller-type polaron formation at metal-insulator transition. The Ba–La–Cu–O system has oxygen-deficient phases with mixed-valent copper, expected to have strong electron-phonon coupling and metallic conductivity. Samples were prepared via coprecipitation from aqueous solutions. X-ray analysis revealed three phases, including a layer-type perovskite-like phase. The third phase is thermally stable up to 1000°C. Conductivity measurements showed metallic behavior at high temperatures, with a sharp resistivity drop at lower temperatures, influenced by current density and annealing conditions.