CRITICAL-BEHAVIOR OF HEAT-CAPACITY AT THE SMECTIC-C-ASTERISK(ALPHA)-SMECTIC-A TRANSITION OF THE ANTIFERROELECTRIC LIQUID-CRYSTAL METHYLHEPTYLOXYCARBONYLPHENYL OCTYLOXYBIPHENYL CARBOXYLATE (MHPOBC)

High resolution ac calorimetric measurements have been carried out nea r the smectic-C-alpha-smectic-A phase transition in an antiferroelect ric liquid crystal 4-(1-methylheptyloxycarbonyl) phenyl 4'-octyloxybip henyl-4-carboxylate. A clear deviation from the extended mean-field La ndau behavior was seen. The data have been analyzed using a renormaliz ation-group expression, including the correction-to-scaling terms. It was found that the heat-capacity anomaly is described well with the th ree-dimensional XY model, in agreement with the theoretical prediction . It was also found that the second-order correction terms play quite an important role.