Domain structures at ferridistortive phase transitions in [N(CH3)4]2ZnBr4 and related crystals

Ferridistortive phase transition in [N(CH 3 ) 4 ] 2 ZnBr 4 crystal has been studied by a polarized microscope. Ordinary domain structures with a-domains which appear below T c =287 K in the absence of external stress have been found not to vanish at the compensation temperature T z =123 K where the monoclinic angle β happens to be 90°, but remain the same as those above and below T z . Square domains surrounded with two kinds of walls which are parallel to the a-axis and the c-axis can be created below T c by external stress. Furthermore the extinction condition of a-wall of square domains has been found to show a distinct change just at T z . This is the first observation of the compensation temperature T z by a polarized microscope.