Dielectric properties of metastable solid MBBA under pressure

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Abstract
Dielectric measurements on metastable solid MBBA were performed in the frequency range from 0.5 to 100 kHz under pressures up to 6 kbar. The application of pressure shifts the dielectric relaxation curves towards higher temperatures. With increasing pressure, the dielectric relaxation strength increases in the low pressure region up to about 3.5 kbar and after that tends to saturate in the high pressure region. The activation parameters, such as the activation enthalpy, entropy and free energy obtained from the linear relation between the logarithmic relaxation frequency and the reciprocal absolute temperature, increase with increasing pressure. The inflection point pt was found to be at about 3.5 kbar on the curves of activation parameters versus pressure. These facts suggest that different relaxation mechanisms should be applied to the low pressure region below pt and the high pressure region above pt. The pressure dependence of the glass transition temperature was inferred from the pressure dependence of the loss maximum temperature.