Local structural investigation of SmFeAsO(1)-(x)F(x) high temperature superconductors

A strong revitalization of the field of high temperature superconductivity (HTSC) has been
induced recently by the discovery of TC 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 SmFeAsO1−xFx 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.