Development of thermoelectric materials using high-pressure synthesis technique

Thermoelectric materials, which convert heat energy directly into electricity, play an important role in providing globally sustainable energy. In recent years, much effort has been exerted in improving thermoelectric efficiency using various modern synthesis methods. The high-pressure synthesis method has various advantages such as the possibility of synthesizing new materials with impossible structures and compositions at ambient pressure. In this review, we will focus on exploring new compounds using a high-pressure apparatus. The high-pressure synthesis and thermoelectric measurement technique will be discussed. In addition, in-situ X-ray diffraction experiments under high temperature and high pressure to determine the conditions for high-pressure synthesis will be discussed. Finally, the thermoelectric properties of several compounds (skutterudites and magnesium silicide) prepared under high pressure will be reviewed

Interplay between elastic fields due to gravity and a partial dislocation for a hard-sphere crystal coherently grown under gravity: driving force for defect disappearance

We previously observed that an intrinsic staking fault shrunk through a glide of a Shockley partial dislocation terminating its lower end in a hard-sphere crystal under gravity coherently grown in by Monte Carlo simulations [Mori et al., Molec. Phys. 105, 1377 (2007)]; it was an answer to a one-decade long standing question why the stacking disorder in colloidal crystals reduced under gravity [Zhu et al., Nature 387, 883 (1997)]. Here, we present an elastic energy calculation; in addition to the self-energy of the partial dislocation [Mori et al., Prog. Theor. Phys. Suppl. 178, 33 (2009)] we calculate the cross-coupling term between elastic field due to gravity and that due to a Shockley partial dislocation. The cross term is a increasing function of the linear dimension R over which the elastic field expands, showing that a driving force arises for the partial dislocation moving toward the upper boundary of a grain.Comment: 8pages, 4figures, to be published in Molecular Physic

Measurement of the Seebeck coefficient under high pressure by dual heating

This study presents a new method for measuring the Seebeck coefficient under high pressure in a multi-anvil apparatus. The application of a dual-heating system enables precise control of the temperature difference between both ends of the sample in a high-pressure environment. Two pairs of W–Re thermocouples were employed at both ends of the sample to monitor and control the temperature difference, and independent probes were arranged to monitor the electromotive force (emf) produced by temperature oscillation at a given target temperature. The temperature difference was controlled within 1 K during the resistivity measurements to eliminate the influence of the emf owing to a sample temperature gradient. The Seebeck measurement was successfully measured from room temperature to 1400 K and was obtained by averaging the two measured values with opposite thermal gradient directions (∼20 K). Thermoelectric properties were measured on disk-shaped p-type Si wafers with two different carrier concentrations as a reference for high Seebeck coefficients. This method is effective to determine the thermoelectric power of materials under pressure

コウヒンシツ コロイド ケッショウ セイチョウ ギジュツ ノ カクリツ

To grow large and high-quality colloidal crystals, several techniques have been investigated. Apparatus for soap-free emulsion polymerization was built up. Synthesis of surfactant-free polystyrene microparticles colloidal dispersions with small diameter dispersion was achieved. Reduction of particle size polydispersity by crystallization, preceded by a thermodynamic consideration, was attempted and worked in few conditions. In-situ observation was found to be a fruitful method to obtain the information of crystallization process

Gravitational tempering in colloidal epitaxy to reduce defects further

Less-defective colloidal crystals can be used as photonic crystals. To this end, colloidal epitaxy was proposed in 1997 as a method to reduce the stacking defects in colloidal crystals. In this method, face-centered cubic (fcc) (001) stacking is forced by a template. In fcc (001) stacking, in contrast to fcc {111} stacking, the stacking sequence is unique, and thus the stacking fault can be avoided. Additionally, in 1997, an effect of gravity that reduces the stacking disorder in hard-sphere (HS) colloidal crystals was found. Recently, we have proposed a gravitational tempering method based on a result of Monte Carlo (MC) simulations using the HS model; after a colloidal crystal is grown in a relatively strong gravitational field, the defects can be reduced by decreasing the gravity strength and maintaining it for a period of time. Here, we demonstrate this method using MC simulations with a programmed gravitation. The dramatic disappearance of defect structures is observed. Gravitational tempering can complement gravitational annealing; some defect structures that accidentally remain after gravitational annealing (keeping the colloidal crystal under gravity of a considerable constant strength) can be erased. © 2014 American Chemical Society

Supramolecular Complexation of \u3cem\u3eN\u3c/em\u3e-Alkyl- and \u3cem\u3eN\u3c/em\u3e,\u3cem\u3eN\u3c/em\u3e′-Dialkylpiperazines with Cucurbit[6]uril in Aqueous Solution and in the Solid State

Water seeds: Complex stoichiometry/composition and degree of oligomerization (oligomeric supramolecular complex formation) of cucurbit[6]uril (CB[6]) with N-alkyl- and N,N′-dialkylpiperazine were investigated in aqueous solutions by means of isothermal titration calorimetry (ITC), ESI-MS, NMR and light scattering measurements. Complex stoichiometry/composition and degree of oligomerization (oligomeric supramolecular complex formation) of cucurbit[6]uril (CB[6]) with N-alkyl- and N,N′-dialkylpiperazine were investigated in aqueous solutions by means of isothermal titration calorimetry (ITC), ESI-MS, NMR and light scattering measurements. It was found that the complex stability and the degree of oligomerization increase with elongating the alkyl chain attached to the piperazine core. X-ray crystallographic studies revealed a clear correlation between the structure of CB[6]–alkylpiperazine crystals obtained from aqueous solutions and the molecular weight/properties of host–guest oligomers existed in the solution as supramolecular “seeds” of crystal formation