The microstructures of SmFeAs(O,F), Ba(Fe,Co)(2)As-2, and FeTe0.5Se0.5 prepared on CaF2 substrates were investigated using transmission electron microscopy. The SmFeAs(O,F)/CaF2 interface is steep, without a disordered layer. By contrast, a chemical reaction occurs at the interface in the cases of Ba(Fe,Co)(2)As-2 and FeTe0.5Se0.5. The reaction layers are located on opposite sides of the interface for Ba(Fe,Co)(2)As-2 and FeTe0.5Se0.5. We found that the lattice distortion of the three superconducting films on the CaF2 substrates enhances the T-C values compared with films prepared on oxide substrates. The origin of this lattice deformation varies depending on the superconducting material. (C) 2014 AIP Publishing LLC.