X-Ray Diffraction Study on a New Incommensurate Phase Transition in Ferroelectric (NH₄)₂ZnCl₄

Abstract

X-ray diffraction from (NH₄)₂ZnCl₄ and its dielectric property were studied. It was confirmed that the crystal in the intermediate phase between the ferroelectric transition point (−4.5°C) and the weak ferroelectric transition point (3°C) is commensurate.
It was found that the crystal has an incommensurate structure (δ≠0) characterized by the (h k l±(1⁄4+δ)) satellite reflections between 91°C and 133°C. The dielectric constant along the b axis shows a small peak at the incommensurate-commensurate phase transition point, 91°C.