Heat capacities of lithium-doped samples of CuO have been measured below room temperature by adiabatic calorimetry. The antiferromagnetic ordering transition to incommensurately modulated state was detected as a step in the heat capacity. Its concentration dependence was compatible with existing reports based on Li-NMR. The incommensurate-commensurate transition of lithium-doped copper oxide was clearly detected. The magnetic phase diagram of Cu1-xLixO was thus constructed. The decrease of both transition temperatures with the Li doping is nearly twice as strong as that expected from mean-field and percolation theories.
(Solid State Commun., 125, 23-26 (2003))
Heat capacities of p-terphenyl based mixed crystals with
3,6-diphenyl-1,2,4,5-tetrazine have been measured by adiabatic
calorimetry below room temperature. Concentration dependence is
examined of the apparent entropy of transition for the twist
transition of the host p-terphenyl crystal, and clearly
shows that the phase transition is of order-disorder type
where the conformation of an individual molecule plays a role of
an Ising spin variable.
(J. Phys.: Condensed Matt., 10, 3359-3366 (1998))
The heat capacities of p-terphenyl and p-terphenyl-d14 were measured between 3 and 300 K. The phase transition associated with a molecular conformation change was observed as a lambda-shaped anomaly at (193.5 +- 0.1) K and at (180.3 +- 0.1) K. The enthalpies of transition are (304 +- 20) J mol-1 and (288 +- 20) J mol-1 and the entropies of transition are (1.63 +- 0.10) J K-1 mol-1 and (1.63 +- 0.10) J K-1 mol-1, respectively. The anisotropy of the intermolecular interaction is discussed and the anomalous portion of the heat capacities in the trasnition region was compared favorably with a two-dimensional Ising model.
(Bull. Chem. Soc. Jpn., 61, 679-688 (1988))