Abstract:
This paper reports on measurements with a high-accuracy universal polarimeter
of the birefringence, optical activity, and indicatrix relation in incommensurately
modulated ((CH3)4N)2ZnCl2.8Br1.2
crystals. It is shown that in this solid solution the inversion symmetry
is broken already in the paraelastic phase, due to the inhomogeneous distribution
of CT and Br over the zinc-halide tetrahedra. This, however, allows one
to study the influence of the incommensurate modulation on a nonzero optical
activity. This influence is clearly shown for a sample in which, moreover,
the modulation wave vector is believed to lock at several commensurate
values.