Triphenyl phosphite was studied by powder X-ray diffractometry, adiabatic calorimetry, and dielectric relaxation measurements. The highly correlated liquid, denoted by LC, phase corresponding with the glacial phase by Cohen et al. was prepared by annealing the ordinary liquid, denoted by LN, at 210 K, and different states in the LC phase were formed by further annealing the prepared LC-phase sample at 215 and 220 K. After the temperature jump from 210 to 215 K, two different processes first of heat absorption and then heat evolution were found to exist in the LC phase. The first process showed reversible temperature dependence of the relaxation times near the temperature of LC-phase formation as far as the process bringing the latter heat evolution effect did not proceed any further. The glass transition temperatures were found to be 209.9, 212.6, and 214.0 K for the LC-phase samples formed at 210, 215, and 220 K, respectively. The fragility parameters of the respective samples were 104, 99, and 94, comparable with 104 in the LN phase. The second process changed the relaxation times of the first process irreversibly to increase as the temperature of LC-phase formation increases in the order of 210, 215, and 220 K. The temperature dependences of β-relaxation times were found to coincide completely with each other between the LN and LC phases. Those results were interpreted by the “intracluster rearrangement for α process” model combined with the “cluster structure for supercooled liquid and glass” model; the above second process corresponds to the increase/decrease in the size of the somehow “structurally ordered” region (named a cluster) and the first one to the order/disorder process of molecules within each cluster, namely the ordinary α process. The above second effect of heat evolution at 215 K is thus due to the development of ordering following the increase in the cluster size. The β relaxation would be attributed to the rearrangement of molecules between the clusters.

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