Determination of the Nature of the Tetragonal to Orthorhombic Phase Transition in SrFe_2As_2 by Measurement of the Local Order Parameter

摘要

SrFe2As2 is the end-member for a series of iron-pnictide superconductors andhas a tetragonal-to-orthorhombic phase transition near 200 K. Previousmacroscopic measurements to determine the nature of the transition gaveseemingly inconsistent results so we use electron microscopy to monitor thelocal order parameter showing that the transformation is first order and thatthe orthorhombic phase grows as needle domains. This suggests the transitionoccurs via the passage of transformation dislocations, explaining the apparentinconsistencies. This mechanism may be common to similar transitions.