We found a subphase with a six-layer periodicity which appears between the ferroelectric SmC(*) and the antiferroelectric SmC(A)(*)(q(T) = 0) phases. The six-layer periodic structure is directly determined by the microbeam resonant x-ray scattering measurement. Furthermore, considering the dielectric constants, this phase was found to be ferrielectric, assigned as SmC(A)(*)(q(T) = 2/3). This subphase indicates the importance of the competition between the ferro- and the antiferroelectric phases and, in that point, it is essentially different from the previously observed six-layer phase. The relation between current theories and our present experimental results has been studied and discussed.
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