Abstract
AbstractTwo compositions in the La‐Ba‐Cu‐Co‐O system − La2Ba3Cu2Co3O13 and La2Ba3Cu3Co2O13 − have been synthesized and characterized by means of SAED (Selected Area Electron Diffraction) and HREM (High Resolution Electron Microscopy). The La2Ba3Cu2Co3O13 phase leads to a fivefold perovskite superstructure along the c axis, which can be described as formed by the recurrent intergrowth of the two alternating blocks ···PP··· and ···POhP··· (P = pyramid and Oh = octahedron). Pyramidal and octahedral sites are randomly occupied by Cu/Co cations, while La/Ba cations exhibit an ordered distribution. The La2Ba3Cu3Co2O13 composition gives rise to a mixture of phases in which a new phase showing a threefold superstructure due to the sequence ···POhP··· coexists with a fivefold superstructure with the same polyhedra sequence (···PPPOhP···) as the previous one, but a disordered arrangement of lanthanum‐barium cations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
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