Gaussian tricritical behavior of heat capacity at the smectic-A-smectic-C liquid crystal transition in a racemic mixture of 4-(1-methylheptyloxycarbonyl)phenyl 4'-octyloxybiphenyl-4-carboxylate

High resolution ac calorimetric measurements have been carried out near the smectic-A-smectic-C phase transition in a racemic mixture of 4-(1-methylheptyloxycarbonyl)phenyl 4'-octyloxybiphenyl-4-carboxylate. The heat capacity data show a distinct pretransitional excess above the transition temperature as well as below it. The data have been analyzed in detail with the renormalization-group expression with correction-to-scaling terms. It was found that the data show Gaussian tricritical behavior. It was also found that the present data support the first-order correction exponent Delta(1) to have a value 0.5. The value of nonuniversal amplitude ratio A(-)/A(+), and the possibility of the existence of the logarithmic corrections have also been discussed.