Neutron Scattering Study on the Incommensurate-Commensurate Phase Transition in Ferroelectric {N(CH3)4}2ZnCl4

Incommensurate satellite reflections at ( h ,0, l ±(1/3-δ)) were measured by neutron scattering for ferroelectric {N(CH 3 ) 4 } 2 ZnCl 4 . In phase II (7.5∼23.6°C) an incommensurate structure (δ≠0) was observed. The parameter δ is about -0.086 at the II-I transition temperature, and the absolute value of δ slightly decreases with decreasing temperature. At the ferroelectric Curie temperature (7.5°C) it tends discontinuously to zero. The results confirm that the ferroelectricity in this material is caused by the incommensurate-to-commensurate phase transition as in the case of K 2 SeO 4 .