Coexistence of a ferroelectric and a ferroelastic domainstructure: (NH₄)₂ZNCL₄ in its phase V

Abstract

Birefringence experiments, X-ray diffraction and X-ray topography show that phase V of (NH₄)₂ZnCl₄ is triclinic. The phase is stable between −2° C and −10° C and has a modulation vector of (2/7)c*. It is only after the crystal has passed several times through the phase transitions that all observations are reproducable. Before that, parts of the crystal are in phase IV and VI, so that satellite reflections are observed simultaneously at (1/4)c*, (2/7)c* and (1/3)c*.