ABSTRACT
The structure of copper oxysalt minerals is analyzed on the basis of the classification scheme developed earlier for synthetic cuprates. The copper-oxygen compounds were considered as the salts of hypothetical copper acids with characteristic Cu-containing structural units of various dimensions formed by a polymerization of the CuO squares. The results of magnetic susceptibility measurements performed recently were analyzed from the viewpoint of the developed extended structural classification scheme. The dimerization of magnetic moments was considered as a property of cuprates which was strongly dependent on the type of Cu-containing structural unit. A further extension of the structural classification scheme for cuprates is also discussed.
ABSTRACT
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+deltaO2+gamma), 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 not equal 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.
ABSTRACT
The modular approach was applied to analyse the structure of complex cuprates. The modular series of various types were distinguished in the family of layered cuprates making use of the classification scheme in a fragment approximation developed earlier. The poly-somatic series were revealed in the groups of cuprates which were expected to possess the properties of both salt and oxide. The structure of the ladder-type cuprates was analysed in more detail. The present study has shown that the polysomatic model can be efficiently applied to the structural analysis of complex cuprates.
