Structural disorder in Li(x)[C5H5N](y)Fe(2-z)Se2 and Cs(x)Fe(2-z)Se2 superconductors studied by M'ossbauer spectroscopy

摘要

Two iron-chalcogenide superconductors Li(x)[C5H5N](y)Fe(2-z)Se2 andCs(x)Fe(2-z)Se2 in the as-prepared and annealed state have been investigated bymeans of the Moessbauer spectroscopy versus temperature. Multi-componentspectra are obtained. One can see a non-magnetic component due to iron locatedin the unperturbed Fe-Se sheets responsible for superconductivity. Remainingcomponents are magnetically ordered even at room temperature. There is somemagnetically ordered iron in Fe-Se sheets perturbed by presence of the ironvacancies. Additionally, one can see iron dispersed between sheets in the formof magnetically ordered high spin trivalent ions, some clusters of above ions,and in the case of pyridine intercalated compound in the form of alpha-Feprecipitates. Pyridine intercalated sample shows traces of superconductivity inthe as-prepared state, while cesium intercalated sample in the as-preparedstate does not show any superconductivity. Superconductors with transitiontemperatures being 40 K and 25 K, respectively, are obtained upon annealing.Annealing leads to removal/ordering of the iron vacancies within Fe-Se sheets,while clusters of alpha-Fe grow in the pyridine intercalated sample.