Evidence of continuous evolution of smectic A2 from smectic Ad

We present here precise measurements of the layer spacing for two compounds, viz. 4-n-heptyloxyphenyl-4'-(4'-cyanobenzoyloxy)benzoate and 4-n-undecyloxyphenyl-4'-(4'-cyanobenzyloxy)benzoate. Contrary to earlier reports our data do not show any jump in the layer spacing at the expected A_d-A₂ transition temperature, showing thereby that for both compounds A₂ evolves continuously from the A_d phase.