RESUMO
A strong revitalization of the field of high temperature superconductivity (HTSC) has been induced recently by the discovery of T(C) around 26 K in F-doped LaFeAsO iron pnictides. Starting from this discovery, a huge amount of experimental data have been accumulated. This important corpus of results will allow the development of suitable theoretical models aimed at describing the basic electronic structure properties and nature of superconducting states in these fascinating new systems. A close correlation between structural features and physical properties of the normal and superconducting states has already been demonstrated in the current literature. Advanced theoretical models are also based on the close correlation with structural properties and in particular with the Fe-As tetrahedral array. As for other complex materials, a deeper understanding of their structure-properties correlation requires a full knowledge of the atomic arrangement within the structure. Here we report an investigation of the local structure in the SmFeAsO1â xF(x) system carried out by means of x-ray total scattering measurements and pair distribution function analysis. The results presented indicate that the local structure of these HTSC significantly differs from the average structure determined by means of traditional diffraction techniques, in particular the distribution of Fe-As bond lengths. In addition, a model for describing the observed discrepancies is presented.
RESUMO
The effect of chemical and hydrostatic pressure has been studied systematically in a selected system belonging to the 1111 family of iron pnictide high-temperature superconductors. The results show a surprising similarity between the trend of critical temperature vs hydrostatic pressure for isoelectronic samples with different rare earths (RE) on the RE site and samples of the SmFeAsO(1-x)F(x) series with different doping levels. These results open new questions about the underlying mechanism for superconductivity in iron pnictides.
RESUMO
In this Article, we provided the complete phase diagram of NdFeAsO(1-x)F(x) solid solution as a function of electron doping thanks to the careful determination of F- and O-content and phase content. We gave direct evidence of the source of F-depletion in the superconducting main phase, that is, the formation of oxyfluoride spurious phase. The approach reported in this work clearly showed that to give reliable results on these complex new superconducting materials, a rigorous control of the chemical composition of the considered phases has to be carried out.
