Abstract
We have carried out a high resolution X-ray study of the smectic phases of Butyloxybenzylidene Octylaniline. We find that the phase previously identified as Smectic-B in this material is crystalline with in-plane order extending over at least 1.4 μm. The in-plane Bragg peaks are accompanied by anomalously strong diffuse scattering that can be described by a form 1/(q 2⊥ + γ2 q 2 z). Unless the elastic constant C44 is more than an order of magnitude smaller than previously reported values of ∼ 108 ergs/cm3 the diffuse scattering can not be due to acoustic phonons. The crystalline-B to Smectic-A melting transition is strongly first order with no observable pre-transition effects on either side of the transition.