  The local structure in high temperature superconductors is nowadays
considered a key point for understanding superconductivity mechanism. MgB2 has
a well-known simple structure; but its local structure remains quite
unexplored. This is due to the fact that typical x-ray local probes, such as
EXAFS, fail when used to study local structure of light atoms, such as Mg and
B. We used high resolution neutron diffraction with pair distribution function
(PDF) analysis for investigating disorder on the atomic scale in the Al doped
Mg1-xAlxB2 system. The results indicate an anisotropic structural inhomogeneity
along the c-axis that could be related with the delocalized metallic-type
bonding between Boron layers.
