ИСТИНА

For the first time, the crystallization conditions of the (M2Cu2O3)m(CuO2)n-type phases were analyzed and the single crystals with the structure close to the unstable β-phase of ladder-type compounds were grown. The obtained results allow one to reveal the regularities in the phase formation of (M2Cu2O3)m(CuO2)n compounds and to specify the conditions for the growth of superconducting (SC) single crystals of incommensurate-type (M2Cu2O3)m(CuO2)n phases. For these compounds, the magnitude of c-parameter but not the Ca-amount is the dominating factor for superconductivity. This is a possible reason for the observation of superconductivity induced by pressure, which reduces the c-parameter.