Development of frequency tuning AC modulation method for high-pressure heat capacity measurements of molecules-based compounds

The automatic frequency tuning method in the high-pressure ac calorimetry system constructed to measure heat capacity for molecules-based compounds with CuBe[Formula: see text]+[Formula: see text]NiCrAl cramp-type pressure cell is reported. This development is performed for increasing resolution and temperature ranges of the heat capacity measurements under external pressure up to 2.0 GPa. The system can check the appropriate conditions by tracing frequency dependence of [Formula: see text] to determine the oscillation frequency at the center of the plateau region of this value. The experiments using the powder samples of metal complexes clarified that the appropriate frequency changes sensitively depending on the difference of temperature and that of external pressures, especially at low temperature region. It decreases with increasing temperature and this relation was found to be almost linear with temperature in ambient pressure and under pressure conditions. The change of thermal diffusion from the sample part to the heat bath should be treated carefully in order to get enough resolution in high pressure AC heat capacity measurements of molecule-based compounds.