Measurement of Smectic- A -Phase Order-Parameter Fluctuations near a Second-Order Smectic- A —Nematic-Phase Transition

The anisotropic liquid-structure factor of p -cyanobenzylidene-amino-p-n-octyloxybenzene has been measured in the nematic phase using Cu Kα x rays. This material exhibits a second-order phase transition to the smectic A phase at Tc=82.8 ^∘{}C. The liquid-structure factor shows a non-Lorentzian peak at a wave number of q₀=0.179 ^-1 (equivalent d spacing 35.0 {}) of the following form: ${S}q=1+{{3.5{{ε}}^{{γ}}+10{[{({q}_{{∥}}{-}{q}₀)}{{q}₀}]}²+0.6{({{q}_{{⊥}}}{{q}₀})}^{{η}}}}^{{-}1}$, where ${ε}={(T{-}{T}c)}{{T}c}$, ${γ}=1.49±{}0.1$, ${η}=2.5±{}0.2$, and ${}{q}_{{∥}}({}{q}_{{⊥}})$ are the momentum transfers parallel (perpendicular) to the orienting field.