A chlorinated liquid crystalline compound, exhibiting paraelectric SmA, ferroelectric SmC*, and antiferroelectric SmC(A)* phases as well as sub-phase alpha, has been studied by means of electrooptic and DSC calorimetry methods. The sub-phase alpha has been observed by reversal current method. To this end the response currents have been measured vs. temperature, electric flied strength and frequency of the driving voltage. It has been found that the reversal current exhibits one peak in the ferroelectric SmC* phase whereas the antiferroelectric phase shows two separated peaks. In the case of the sub-phase alpha (SmC*(alpha)) a characteristic shape of the response current in the form of a doublet has been observed in a narrow temperature range between the SmA* and SmC* phases. Spontaneous polarisation and tilt angle have been evaluated as a function of temperature. The electrooptic measurements have been carried out on a single mono-domain grown under a strong electric field during slow cooling from the paraelectric SmA* to antiferroelectric phase.