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INTRODUCTIONParticular interest in layered perovskite-like compounds, including superconducting cuprates, is explained by the possibility of preparing and applying different functional inorganic materials (microcomposites, etc.) based on compounds of this class [1,2]. The stability of layered compounds and solid solutions based on them, the influence of different isomorphous substitutions in the crystal lattice on the electrical properties, and the choice of optimum chemical compositions with controlled electrical properties are important problems. The solution of these problems will allow one to reveal composition-substitution-structureproperty correlations, which are of great practical significance [3].In this work, we studied two series of yttrium cuprates with an YBa 2 Cu 3 O 7 -δ -type (123) structure, which were prepared by isovalent and heterovalent substitutions.Substitution of zinc atoms for copper or calcium atoms for yttrium in the Y-123 system has been investigated in a large number of works [4][5][6]. Simultaneous replacement of copper and yttrium was studied only by Naqib et al.[7] at a fixed calcium content ( x = 0.05). A series of compounds of the general formula Y 1 − x Ca x Ba 2 Cu 3 -y Zn y O 7 -δ is systematically investigated for the first time. Interest in the compounds studied in our work is motivated by the influence of calcium ions on the oxygen sublattice (as is known from the data available in the literature, an increase in the calcium content leads to a decrease in the oxygen content). Moreover, replacement of yttrium cations by larger calcium cations results in the stabilization of the structure due to the elimination of the steric effect associated with the repulsion of oxygen ions in an YO 8 polyhedron [3]. Furthermore, calcium has a specific effect on the critical temperature T c of the transition to a superconducting state (this temperature for Y-123 is approximately equal to 93 K). For example, an increase in the calcium content in the Y-123 system leads to a decrease in the critical temperature from 93 to 79 K for compounds with an oxygen content of 7.0 in the initial (without calcium) sample and to an increase in this temperature from 63 to 81 K for compounds with an oxygen content of 6.8 in the initial sample [8,9]. Note also that calcium recovers the superconductivity in materials with double substitutions. In particular, this effect was observed when calcium was used for doping materials in which chain copper atoms or barium atoms were preliminarily substituted in part for cobalt or lanthanum atoms, respectively [9].The purpose of the present work was to investigate the influence of the calcium content on the critical temperature of compounds in which planar copper atoms are partially substituted for zinc atoms and, vice versa, the effect of the zinc content on the critical temperature upon partial substitution of calcium atoms for yttrium atoms. The results obtained were compared with those available in the literature for the series of the above compounds [9]. In addition, ...