Phase transition in (NH4)3FeF6

By use of Mössbauer spectroscopy we have found that the transition from tetragonal to cubic structure in (NH₄)₃FeF₆ takes place at 263 K. The phase transition exhibits a hysteresis of 0.5 K. The experimental data indicate that the tetragonal deformation found at low temperatures diminishes gradually as the transition temperature is approached. The spectra are influenced by electronic relaxation.