Polar Smectic subphases: phase diagrams, structures and X-ray scattering
P. V. Dolganov, V. M. Zhilin, V. E. Dmitrienko+, E. I. Kats*
Institute of Solid State Physics RAS, 142432 Chernogolovka, Moscow Reg., Russia
+A. V. Shubnikov Institute of Crystallography, 119333 Moscow, Russia
*Laue-Langevin Institute, F-38042 Grenoble, France
*L. D. Landau Institute for Theoretical Physics RAS, 117334 Moscow, Russia
PACS: 61.30.Eb, 64.70.Md, 68.10.Cr
Abstract
We analyze a discrete phenomenological model accounting for phase
transitions and structures of polar Smectic-C* liquid
crystalline phases. The model predicts a sequence of phases
observed in experiment: antiferroelectric SmC*A -
ferrielectric SmC*FI1 - antiferroelectric SmC*FI2
(three and four layer periodic, respectively) - incommensurate
SmC*α - SmA. We find that in the three-layer
SmC*FI1 structure both the phase and the module of the order
parameter (tilt angle) differ in smectic layers. This modulation
of the tilt angle (and therefore of the layer spacing d) must
lead to X-ray diffraction at the wave vectors Qs=2π s/d
(
even for the non-resonant scattering.