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.