The structures of cubic phases of 4'-n-alkoxy-3'-nitrobiphenyl-4-carboxylic acids (ANBC-n, where n is the number of carbon atoms in the alkoxy group) have been studied by X-ray diffraction technique. It was found that the cubic region of ANBC-n contains two types of cubic phases, Cub I with Im3m symmetry and Cub II with Ia3d. Very surprisingly, the phase type of cubic phases of ANBC-19, -20, and -21 is of Im3m type in the whole temperture region of each, and thus, the region of Ia3d type is divided into two, n=15-18 and n≧22.
