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Order-disorder in T, T', and T* phase: superconductors and related materials
J M González-Calbet1, M J Sayagués, A Varela
1Departamento de Química Inorgánica, Facultad de Químicas, Universidad Complutense, Madrid, Spain.
Abstract:
After reviewing microstructural studies on superconducting materials showing T, T', and T* structural types, results are presented on the microstructure of some n-type superconductors and related materials prepared with accurate control of the oxygen stoichiometry. Electron microscopy is used to describe the ordering of interstitial oxygen defects in T-type La2NiO4 + delta leading to the formation of the n = 2 term of a homologous series with the general formula La8nNi4nO16n + 1. Structural transitions and superstructure formation in the Pr2-x-yCexSryCuO4-delta system are reported, where T, T', and T* phases are isolated as a function of both Ce and Sr content.