Structural Phase Transition of Layer Compound (C₂H₅NH₃)₂FeCl₄

Abstract

The sequence of the structural phase transitions of the layer compound (C₂H₅NH₃)₂FeCl₄ has been determined with the ultrasonic, dielectric and polarized microscope measurements as following; Phase I (D_4h¹⁷)—(378.8 K)—Phase II (D_2h¹⁸)—(203.5 K)—Phase III—(133.7 K)—Phase IV. The set of the critical exponents obtained with ultrasonic methods are explained by the results of the renormalization group theory on the three dimensional XY model. The ferroelastic domains are observed in the phase II and phse III. The anomaly of the dielectric constant is found near the II–III phase transition point.