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 nea r the smectic-A-smectic-C phase transition in a racemic mixture of 4-( 1-methylheptyloxycarbonyl)phenyl 4'-octyloxybiphenyl-4-carboxylate. Th e heat capacity data show a distinct pretransitional excess above the transition temperature as well as below it. The data have been analyze d 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-o rder correction exponent Delta(1) to have a value 0.5. The value of no nuniversal amplitude ratio A(-)/A(+), and the possibility of the exist ence of the logarithmic corrections have also been discussed.