A Study of the Transitions Smectic A—Hexatic B and Hexatic B—Crystal B By X-Ray Diffraction

Abstract

The phase transitions Smectic A—hexatic B and hexatic B—crystal B for the pure compound 4-propionyl-4'-n-heptanoyloxyazobenzene have been investigated by X-ray diffraction.

Pretransitional effects have been observed in the Smectic A phase.

The temperature dependence of the in-plane positional coherence length ξ_‖ has been determined from the large angle diffusion peak, associated with an in-plane structure factor of Lorentzian shape, as predicted by theory.

ξ_‖ values vary in the hexactic phase from ξ_‖ ≅ 100 A to ξ_‖ ≅ 40 Å in the range of temperature from 88.7 ° C to 85.6 ° C, in very good agreement with previous results of Pindak et al. on a single crystal of a compound showing only the hexatic B and no crystal B phase.