Reduction of thermal conductivity κ while preserving high electrical conductivity σ in materials continues to be a vital goal in thermoelectric study for the reuse of exhaust heat energy. In the use of an eco-friendly and ubiquitous element, Si as thermoelectric material, high κ value in bulk Si is the essential bottleneck to achieve high dimensionless figure of merit. This is a motivation for many recent studies on reducing κ in Si, by nanostructuring, e.g., using grains/wires with size smaller than the phonon mean free path. However, κ reduction that can be achieved tends to be saturated presumably due to an amorphous limit. Here, we present a nanoarchitecture for defeating the κ amorphous limit while preserving bulk-like σ. This new nanoarchitecture is an assembly of Si nanocrystals with oriented crystals separated by a 1-monolayer amorphous layer with well-controlled nanoscale shaped interfaces. At these interfaces, novel phonon scattering occurs resulting in κ reduction below the amorphous limit. Preservation of bulk-like σ results from the coherency of the carrier wavefunctions among the oriented nanocrystals separated by the ultrathin amorphous layer.

Heat capacity of a halogen-bridged quasi-one-dimensional mixed-valence binuclear metal complex ͑the so-called M M X chain͒, Pt 2 (n-BuCS 2 ) 4 I, was measured by adiabatic calorimetry. First-order phase transitions were observed at 213.5 K and 323.5 K. For the former, the enthalpy and entropy of transition were 4.29 kJ mol Ϫ1 and 20.09 J K Ϫ1 mol Ϫ1 , respectively. Those of the latter were 2.41 kJ mol Ϫ1 and 7.46 J K Ϫ1 mol Ϫ1 , respectively. Another thermal anomaly probably due to a higher-order phase transition was detected at 114 K. The magnitude of the entropy of transition shows that, upon heating, the butyl chains in one-third complexes in crystalline Pt 2 (n-BuCS 2 ) 4 I are changed from an ordered state to a disordered state through the phase transition at 213.5 K, and resume the ordered state from this disordered state at 323.5 K. The transition at 213.5 K involves a ''spin-Peierls'' contribution beyond the structural one.

The spin crossover phenomenon of the recently described spin crossover complex [FeII(DAPP)(abpt)](ClO4)2 [DAPP = bis(3-aminopropyl)(2-pyridylmethyl)amine, abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole] accompanying an order-disorder phase transition of the ligand was investigated by adiabatic heat capacity calorimetry, far-IR, IR, and Raman spectroscopies, and normal vibrational mode calculation. A large heat capacity peak due to the spin crossover transition was observed at T(trs) = 185.61 K. The transition enthalpy and entropy amounted to Delta(trs)H = 15.44 kJ mol-1 and Delta(trs)S = 83.74 J K-1 mol-1, respectively. The transition entropy is larger than the expected value 60.66 J K-1 mol-1, which is contributed from the spin multiplicity (R ln 5; R: the gas constant), disordering of the carbon atom of the six-membered metallocycle in the DAPP ligand, and one of the two perchlorate anions (2R ln 2), and change of the normal vibrational modes between the high-spin (HS) and low-spin (LS) states (35.75 J K-1 mol-1). The remaining entropy would be ascribed to changes of the lattice vibrations and molecular librations between the HS and LS states. Furthermore, [Fe(DAPP)(abpt)](ClO4)2 crystals disintegrated and became smaller crystallites whenever they experienced the phase transition. This may be regarded as a successive self-grinding effect, evidenced by adiabatic calorimetry, DSC, magnetic susceptibility, and microscope observation. The relationship between the crystal size and the physical quantities is discussed.

To study the relation between the structural characteristics and the phonon property in the negative thermal expansion (NTE) compounds, the heat capacities of Sc2W3O12 and Sc2Mo3O12 were measured. Spectrum analysis of heat capacity provided their effective phonon densities of states (DOS). The DOS of Sc2W3O12 shows three features; low-energy phonon modes with negative mode-Grüneisen parameter (γ i ) around 5 meV, high-energy phonon modes, and separation of phonon DOS into two regions with a wide gap. The relative contribution of γ i C i , where C i is heat capacity of each vibrational mode i, reveals that the low-energy phonon modes with negative γ i cause the NTE and that the latter two features are necessary to maintain the NTE in a wide temperature range. Sc2Mo3O12 has the low-energy mode with the negative γ i . This fact indicates that Sc2Mo3O12 potentially has the NTE property even in its low-temperature phase showing positive thermal expansion. A comparison of the phonon DOS with other oxides shows that the phonon features are common in the NTE oxides and related to their common chemical and structural characteristics, “strong bond” and “framework structure”. This finding gives us an important guide to search for new actual and/or potential NTE compounds.

Molecular dynamics and resulting disorder in the soft crystal, smectic E (SmE) phase, were studied in detail for the title compound, 4-butyl-4'-isothiocyano-1,1'-biphenyl (4TCB), by (1)H NMR spectroscopy and adiabatic calorimetry. The ordered crystal phase of 4TCB was realized for the first time under ambient pressure after long two-step annealing and used as the reference state in the analysis of the experimental results. Four motional modes were identified in the SmE phase through the analysis of the (1)H NMR T(1). The residual entropy was determined as ca. 6 J K(-1) mol(-1). This magnitude implies that most of the disorder in the SmE phase at high temperatures is removed on cooling except for the head-to-tail disorder of the rod-shaped 4TCB molecule. Standard thermodynamic functions are tabulated below 375 K.

The heat capacity of a halogen-bridged quasi-one-dimensional (Q1D) mixed-valence binuclear metal complex (the so-called MMX chain), Pt 2 (n-PrCS 2 ) 4 I, was measured by adiabatic calorimetry. A higher order phase transition due to structural disorder was observed at 209 K. Another first-order phase transition having a large tail on the low-temperature side was detected at 358.8 K. Their enthalpy and entropy of transition were determined and analyzed. As evidenced by the magnitude of the entropy of transition, similar structural disorder occurs at the corresponding phase transition in Pt 2 (n-PrCS 2 ) 4 I and Pt 2 (n-BuCS 2 ) 4 I, but the shape of thermal anomaly is largely different between the two. The magnitude of the entropy of transition shows that the change of both structural disorder and electronic states occurs simultaneously in a gradual manner on the low-temperature tail of the thermal anomaly at 358.8 K. The change in entropy assignable to the Q1D electron system was estimated as about 2.3 J K -1 mol -1 .

Heat capacity of halogen-bridged one-dimensional binuclear metal complex (so-called MMX chain) having four n-pentyl groups, Pt2(n-PenCS2)4I, was measured by adiabatic calorimetry. A first-order phase transition was observed at 207.4 K when measurement was made after cooling from room temperature. The enthalpy and entropy of transition were determined to be 10.19 kJ mol(-1) and 49.1 J K(-1) mol(-1), respectively. A monotropic phase transition was observed at 324 K on heating, and the entropy of transition was essentially null. The sample once heated above 324 K never returned to the initial phase at room temperature and underwent a higher-order phase transition at 173 K and a first-order phase transition at 220.5 K. The enthalpy and entropy of the first-order phase transition were estimated to be 11.6 kJ mol(-1) and 52.4 J K(-1) mol(-1), respectively. The magnitude of the entropy gain at the phase transition from the initial room-temperature phase to the high-temperature phase at 324 K shows that in Pt2(n-PenCS2)4I a large amount of entropy reserved in alkyl chain is transferred to dithiocarboxylato groups upon the phase transition, as in the cases of Pt2(n-PrCS2)4I and Pt2(n-BuCS2)4I.

The heat capacities were measured by adiabatic calorimetry down to 6 K on both the right-handed isomer and a racemic mixture of 4-(1-methylheptyloxy)-4‘-cyanobiphenyl. A thermodynamic relationship between two crystalline phases has been established and inversion between the stable and the metastable crystals has been found for the isomer. The contradiction between a previous calorimetric study and the results of inelastic neutron scattering and infrared spectroscopy has been resolved. No crystallization was detected for the racemic mixture. The behavior around the glass transition has been analyzed.