Colloidal synthesis and thermoelectric properties of La-doped SrTiO3 nanoparticles

We describe n-type nanostructured bulk thermoelectric La-doped SrTiO3 materials produced by spark plasma sintering of chemically synthesized colloidal nanocrystals. The La doping levels could be readily controlled from 3 to 9.0 at% by varying the experimental conditions. We found that nanoscale interfaces were preserved even after the sintering process, and the thermoelectric properties of the nanostructured bulk La-doped SrTiO3 were characterized. An enhanced thermoelectric efficiency was observed and attributed to the large decrease in thermal conductivity obtained with no significant change in the Seebeck coefficient or electrical conductivity. The nanostructured bulk of the La-doped SrTiO3 exhibited a maximum ZT of similar to 0.37 at 973 K at 9.0 at% La doping, which is one of the highest values reported for doped SrTiO3. Furthermore, the materials showed high thermal stability, which is important for practical high-temperature thermoelectric applications. This report demonstrates the high potential for low-cost thermoelectric energy production using highly stable and inexpensive oxide materials.close97

Dimension-controlled synthesis of CdS nanocrystals: From 0D quantum dots to 2D nanoplates

The dimension-controlled synthesis of CdS nanocrystals in the strong quantum confinement regime is reported. Zero-, one-, and two-dimensional CdS nanocrystals are selectively synthesized via low-temperature reactions using alkylamines as surface-capping ligands. The shape of the nanocrystals is controlled systematically by using different amines and reaction conditions. The 2D nanoplates have a uniform thickness as low as 1.2 nm. Furthermore, their optical absorption and emission spectra show very narrow peaks indicating extremely uniform thickness. It is demonstrated that 2D nanoplates are generated by 2D assembly of CdS magic-sized clusters formed at the nucleation stage, and subsequent attachment of the clusters. The stability of magic-sized clusters in amine solvent strongly influences the final shapes of the nanocrystals. The thickness of the nanoplates increases in a stepwise manner while retaining their uniformity, similar to the growth behavior of inorganic clusters. The 2D CdS nanoplates are a new type of quantum well with novel nanoscale properties in the strong quantum confinement regime.

n-Type Nanostructured Thermoelectric Materials Prepared from Chemically Synthesized Ultrathin Bi₂Te₃ Nanoplates

We herein report on the large-scale synthesis of ultrathin Bi₂Te₃ nanoplates and subsequent spark plasma sintering to fabricate n-type nanostructured bulk thermoelectric materials. Bi₂Te₃ nanoplates were synthesized by the reaction between bismuth thiolate and tri-n-octylphosphine telluride in oleylamine. The thickness of the nanoplates was ∼1 nm, which corresponds to a single layer in Bi₂Te₃ crystals. Bi₂Te₃ nanostructured bulk materials were prepared by sintering of surfactant-removed Bi₂Te₃ nanoplates using spark plasma sintering. We found that the grain size and density were strongly dependent on the sintering temperature, and we investigated the effect of the sintering temperature on the thermoelectric properties of the Bi₂Te₃ nanostructured bulk materials. The electrical conductivities increased with an increase in the sintering temperature, owing to the decreased interface density arising from the grain growth and densification. The Seebeck coefficients roughly decreased with an increase in the sintering temperature. Interestingly, the electron concentrations and mobilities strongly depended on the sintering temperature, suggesting the potential barrier scattering at interfaces and the doping effect of defects and organic residues. The thermal conductivities also increased with an increase in the sintering temperature because of grain growth and densification. The maximum thermoelectric figure-of-merit, ZT, is 0.62 at 400 K, which is one of the highest among the reported values of n-type nanostructured materials based on chemically synthesized nanoparticles. This increase in ZT shows the possibility of the preparation of highly efficient thermoelectric materials by chemical synthesis

n-Type Nanostructured Thermoelectric Materials Prepared from Chemically Synthesized Ultrathin Bi2Te3 Nanoplates

We herein report on the large-scale synthesis of ultrathin Bi 2Te 3 nanoplates and subsequent spark plasma sintering to fabricate n-type nanostructured bulk thermoelectric materials. Bi 2Te 3 nanoplates were synthesized by the reaction between bismuth thiolate and tri-n-octylphosphine telluride in oleylamine. The thickness of the nanoplates was ???1 nm, which corresponds to a single layer in Bi 2Te 3 crystals. Bi 2Te 3 nanostructured bulk materials were prepared by sintering of surfactant-removed Bi 2Te 3 nanoplates using spark plasma sintering. We found that the grain size and density were strongly dependent on the sintering temperature, and we investigated the effect of the sintering temperature on the thermoelectric properties of the Bi 2Te 3 nanostructured bulk materials. The electrical conductivities increased with an increase in the sintering temperature, owing to the decreased interface density arising from the grain growth and densification. The Seebeck coefficients roughly decreased with an increase in the sintering temperature. Interestingly, the electron concentrations and mobilities strongly depended on the sintering temperature, suggesting the potential barrier scattering at interfaces and the doping effect of defects and organic residues. The thermal conductivities also increased with an increase in the sintering temperature because of grain growth and densification. The maximum thermoelectric figure-of-merit, ZT, is 0.62 at 400 K, which is one of the highest among the reported values of n-type nanostructured materials based on chemically synthesized nanoparticles. This increase in ZT shows the possibility of the preparation of highly efficient thermoelectric materials by chemical synthesis.close5