Pylypenko A. Synthesis and properties of HTSC compounds in the Ln-Ba-Cu-O system

The thesis is devoted to optimization of synthesis methods of complex oxide compositions of the family Ln-Ba-Cu-O and selection of the most optimal method of synthesis for obtaining and further investigation of new superconducting compounds. The compounds: Ln3Ba5Cu8O18+δ (Ln: Nd, Sm, Eu, Gd, Dy, Ho), Y2Ba5Cu7Ox and Ln2Ba5Cu7Ox (Ln: Nd, Sm, Eu, Gd) were synthesized by solid state reaction and sol-gel methods. Samples of phase composition are synthesized using the classical ceramic method - Y1-xBixBa2Cu3O7-δ (0≤x≤0,25). Using spectroscopic, X-ray diffraction analyzes, phase formation processes were investigated and the optimal modes of heat treatment for the obtained samples were revealed. It has been established that the optimal synthesis method for these phases is the sol-gel technology. For the Y-358 phase, microcrystal sizes were determined in three ways: using SEM, the Williamson-Hall method and the Sherrer formula. Using iodometric titration, the average degree of oxidation of cuprum and the oxygen index of samples were established. The phase composition of the samples and their crystallographic parameters are determined. The synthesized samples that crystallize in the orthorhombic symmetry have the transition temperature to the superconducting state above the boiling point of liquid nitrogen.