Single-phase polycrystalline samples of Sm1Ba2Cu3O6+y (123 SmSS) with x = 0.0-0.7 were prepared in air by solid state synthesis with precisely controlled technological parameters (the heating and cooling rates, temperature-time regime). Microstructural, structural, and superconducting properties were studied. It is shown that cation stoichiometric samples of Sm1Ba2Cu3O6+y with a high temperature superconducting transition (89-92K) can be obtained in air. By increasing the Sm/Ba ratio in Sm1+xBa2-xCu3O6+y the orthorhombic-to-tetragonal phase transition is observed. The orthorhombic phase loses its stability at x > 0.125, and the solid solution decomposes by a spinodal mechanism to form layered microstructures with a variable Sm/ Ba ratio. The data obtained are useful for understanding the mechanisms of the formation of possible vortex pinning centers in Ln1+xBa2-xCu3O6+y phases.

Keywords: A. inorganic compounds, B. chemical synthesis, C. electron microscopy, C. X-ray diffraction, D. superconductivity.