  We report time-of-flight neutron powder diffraction results on stoichiometric
BaFe2As2. Pair distribution function analysis shows that the orthorhombic
distortion in the a-b plane at short distances are significantly different from
the average lattice distortion, indicating local variations in the lattice at
the short-range. We propose that this local variation reflects a high density
of nano-twins, short-ranged structures which locally affect the magnetic
alignment. This results suggests that the discrepancies between the observed
and calculated magnetic moments in BaFe2As2 arise partly from short-ranged
variation of the lattice in the a-b plane.

Superconductivity