New aspects in the crystal chemistry of (M2Cu2O3)m(CuO2)n-type (M = Ca, Sr, Y, Bi) cuprates

• Published in: Acta crystallographica. Section A, Foundations of crystallography Foundations of crystallography, 2000-03, Vol.56 (2), p.149-156
• Main Authors: Leonyuk, L., Babonas, G.-J., Chernyshov, V., Rybakov, V., Maltsev, V., Baran, M.
• Format: Article
• Language: English
• Subjects: cuprates with ladder-type planes
• ISSN: 0108-7673; 1600-5724
• DOI: 10.1107/S0108767399014889

The structural regularities of (M2Cu2O3)m(CuO2)n‐type (M = Ca, Sr, Y, Bi) cuprates with ladder‐type planes have been considered. On the basis of the structural studies of the samples grown by floating‐zone and flux methods, it was concluded that the phase (M2Cu2O3)(Cu1+δO2+γ), described as the m/n = 1/1 member, with Cu‐deficient Cu—O ribbons in the series (M2Cu2O3)m(CuO2)n can be treated as an individual structural type intermediate between SrCu2O3 and incommensurate‐type phases (M2Cu2O3)m(CuO2)n with m≠n. The deficiency of the Cu sites in CuO ribbons is a particular crystal‐chemistry feature of this structural type, in addition to the geometrical feature (m = n). The structural type of the `Cu‐deficient ladder' can transform into the incommensurate‐type phases (M2Cu2O3)m(CuO2)n (m/n = 5/7, 7/10, 9/13 etc.) in the presence of free [CuO4]6− radicals in the melt. A realization of the (M2Cu2O3)m(CuO2)n phase with a particular m/n value is caused by the type of M cation. On the basis of recent data, the role of trivalent ions in the chemical composition of the (M2Cu2O3)m(CuO2)n‐type compounds was also analyzed. The occurrence of the superconductivity in (Sr, Ca)CuO2 samples is discussed by analogy with cuprates of the infinite‐layer structure.