The structure of frustrated smectic phases exhibited by binary mixtures of 4-n-octyloxyphenyl-4’-cyanobenzoyloxybenzoate (DB8OCN) and 4-n-octyloxybenzoate-4’-cyanoazobenzene (8OBCAB) have been studied by high-resolution x-ray diffraction. This system was previously reported to exhibit three incommensurate smectic-A phases. These incommensurate smectic ${\mathit{A}}_{\mathit{i}1}$,${\mathit{A}}_{\mathit{i}2}$, and the soliton ${\mathit{A}}_{\mathit{i}\mathit{s}}$ phases are found to be coexistences of ${\mathit{A}}_{\mathit{d}}$ and ${\mathit{A}}_1$;${\mathit{A}}_{\mathit{d}}$ and ${\mathit{A}}_2$; and ${\mathit{A}}_{\mathit{d}}$,${\mathit{A}}_1$, and ${\mathit{A}}_2$ phases, respectively. As of now, there are no known incommensurate smectic-A phases.

• Received 20 April 1992

DOI:https://doi.org/10.1103/PhysRevLett.69.301