  A true understanding of the properties of pnictide superconductors require
the development of high-quality materials and performing measurements designed
to unravel their intrinsic properties and short-range nematic correlations
which are often obscured by extrinsic effects such as poor crystallinity,
inhomogeneity, domain formation and twinning. In this paper, we report the
systematic growth of high-quality Na-substituted BaFe2As2 single crystals and
their characterization using pulsed-magnetic fields x-ray diffraction and x-ray
diffuse scattering. Analysis of the properties and compositions of the highest
quality crystals show that their actual Na stoichiometry is about 50-60% of the
nominal content and that the targeted production of crystals with specific
compositions is accessible. We derived a reliable equation to estimate the Na
stoichiometry based on the measured superconducting TC of these materials.
Attempting to force spin reorientation and induce tetragonality, orthorhombic
Ba1-xNaxFe2As2 single crystals subjected to out-of-plane magnetic fields up to
31.4T are found to exhibit strong in-plane magnetic anisotropy demonstrated by
the insufficiency of such high fields in manipulating the relative population
of their twinned domains or in suppressing the orthorhombic order. Broad x-ray
diffuse intensity rods observed at temperatures between 30 K and 300 K uncover
short-range structural correlations. Local structure modeling together with
3D-{\Delta}PDF mapping of real-space interatomic vectors show that the diffuse
scattering arises from in-plane short-range chemical correlations of the Ba and
Na atoms coupled with short-range atomic displacements within the same plane
due to an effective size difference between the two atomic species.
