  Crystal structures and microstructural features, such as structural phase
transitions, defect structures, chemical and structural inhomogeneities, are
known to have profound effects on the physical properties of superconducting
materials. Recently, a large amount of works on the structural properties of
Fe-based high-Tc superconductors have been published. This review article will
mainly focus on typical microstructural features in samples that have been well
characterized by physical measurements. (a) Certain common structural features
are discussed. In particular, crystal structural features for different
superconducting families, local structural distortions in the Fe2Pn2 (Pn=P, As,
Sb) or Fe2Ch2 (Ch=S, Se, Te) blocks, and structural transformations in the 122
system. (b) In FeTe(Se) (11-family), the superconductivity, chemical and
structural inhomogeneities are investigated and discussed in correlation with
superconductivity. (c) In K0.8Fe1.6+xSe2 system, we focus on typical compounds
with emphasis on Fe-vacancy order and phase separations. The microstructural
features in other superconducting materials are also briefly discussed.
