Direct study of structural phase transformation in single crystalline bulk and thin film BaFe2As2

Abstract The ternary iron arsenide compound BaFe 2 As 2 exhibits a structural phase transition from tetragonal to orthorhombic at a temperature of about 140 K. The twin lamellae arising below this transition temperature were studied in undoped single crystalline bulk and epitaxial thin film samples using electron backscatter diffraction in a scanning electron microscope equipped with a helium cryostat. Applying this technique on bulk single crystals a characteristic twin lamella size in the range of 0.1 μm up to a few μm was observed. In contrast, in epitaxially strained thin films the phase transition is not observed at temperatures above 19 K.