Influence of incommensurate modulation on the optical properties of the solid solution ((CH3)4<

Abstract

This paper reports on measurements with a high-accuracy universal polarimeter of the birefringence, optical activity, and indicatrix rotation in incommensurately modulated ((CH 3 ) 4 N) 2 ZnCl 2.8 Br 1.2 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 Cl 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. ͓S0163-1829͑96͒03129-3͔

Microscopic Dielectric and Gyration Tensors of Incommensurately Modulated Insulators

“…The results of our study may be useful for interpreting the influence of the IC modulation on the optical activity (see the experimental results [5]). We remind again that the given subject is poorly worked out from both the experimental and theoretical viewpoints, in contrast to the birefringence phenomena.…”

“…The optical activity in the IC insulators has been studied in much less detail. Up to date the mechanisms for the influence of the IC modulation on the effect are not reliably clarified, though a few experimental results seem to be interesting [5]. Of particular mentioning are the experimental observations of the gyration effect in a number of A 2 BX 4group crystals whose IC phases have inversion symmetry (see, e.g., the recent works [6][7][8] and references therein).…”

Temperature dependence of optical activity and circular dichroism in α‐ZnP2 crystals

“…On the other hand, it is our experience that the typical magnitudes of p 0 and dY are of the order of 10 À4 [11,13,14] and so, as a first approximation, we can estimate kðTÞ with the accuracy better than 10%, when simply neglecting the term p 0 =2. Under similar circumstances, the same approximation has been often used within the HAUP technique [26,27]. Using the kðTÞ data obtained this way, the standard results for the linear birefringence Dn and the relation g 11 = n n ¼ 2k Dn, it is easy to arrive at the temperature dependence of the circular birefringence g 11 = n n shown in Fig.…”