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| 2. |
- Brown, D. R., et al.
(author)
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Relating phase transition heat capacity to thermal conductivity and effusivity in Cu2Se
- 2016
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In: Physica Status Solidi - Rapid Research Letetrs. - : Wiley. - 1862-6254 .- 1862-6270. ; 10:8, s. 618-621
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Journal article (peer-reviewed)abstract
- Accurate measurement of thermal conductivity is essential to determine the thermoelectric figure-of-merit, zT. Near the phase transition of Cu2Se at 410 K, the transport properties change rapidly with temperature, and there is a concurrent peak in measured heat capacity from differential scanning calorimetry (DSC). Interpreting the origin as a broad increase in heat capacity or as a transient resulted in a three-fold difference in the reported zT in two recent publications. To resolve this discrepancy, thermal effusivity was deduced from thermal conductivity and diffusivity measurements via the transient plane source (TPS) method and compared with that calculated from thermal diffusivity and the two interpretations of the DSC data for heat capacity. The comparison shows that the DSC measurement gave the heat capacity relevant for calculation of the thermal conductivity of Cu2Se. The thermal conductivity calculated this way follows the electronic contribution to thermal conductivity closely, and hence the main cause of the zT peak is concluded to be the enhanced Seebeck coefficient.
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| 3. |
- Cederkrantz, Daniel, 1979, et al.
(author)
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Enhanced thermoelectric properties of Mg2Si by addition of TiO2 nanoparticles
- 2012
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 111:2
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Journal article (peer-reviewed)abstract
- The effects on the thermoelectric properties of Mg2Si when adding TiO2 nanoparticles have been evaluated experimentally. A batch of Mg2Si was prepared through direct solid state reaction and divided into portions which were mechanically mixed with different amounts of TiO2 nanoparticles ranging from 0.5 to 3 vol% and subsequently sintered to disks. All materials showed n-type conduction and the absolute value of the Seebeck coefficient was reduced with increasing amount of TiO2 added, while the electrical resistivity was greatly reduced. The thermal conductivity was surprisingly little affected by the addition of the nanoparticles. An optimum value of the thermoelectric figure-of-merit ZT = TS2 sigma/k was found for the addition of 1 vol% TiO2, showing almost three times higher ZT value than that of the pure Mg2Si. Larger TiO2 additions resulted in lower ZT values and with 3 vol% added TiO2 the ZT was comparable to the pure Mg2Si. The sintering process resulted in reduction or chemical reaction of all TiO2 to TiSi2 and possibly elemental titanium as well as reduced TiOx. The increased electrical conductivity and the decreased Seebeck coefficient were found due to an increased charge carrier concentration, likely caused by the included compounds or titanium-doping of the Mg2Si matrix. The low observed effect on the thermal conductivity of the composites may be explained by the relatively higher thermal conductivity of the included compounds, counter-balancing the expected increased grain boundary scattering. Alternatively, the introduction of compounds does not significantly increase the concentration of scattering grain boundaries.
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| 5. |
- Sizov, Andrey, 1989, et al.
(author)
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Influence of Phase Separation and Spinodal Decomposition on Microstructure of Mg₂Si₁₋ₓSnₓ Alloys
- 2019
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In: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7505 .- 1528-7483. ; 19:9, s. 4927-4933
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Journal article (peer-reviewed)abstract
- Mg2Si1-xSnx alloys with nominal values of x [0.03:0.18] were synthesized at 780 °C by solid-state reaction from Mg2Si and Mg2Sn and subsequently annealed at either 680 or 580 °C. Their microstructure was investigated by X-ray diffraction using the Rietveld method. Depending on the treatment temperature and the nominal composition, the solid solutions split into different Si- and/or Sn-rich Mg2Si1-xSnx phases. Traces of spinodal decomposition were observed for the samples with a low Sn content independent of treatment temperature due to the limited diffusion kinetics when entering the miscibility gap. A similar effect was observed when applying a higher cooling rate to the samples with higher Sn concentration. In this case, the samples experience thermodynamic spinodal decomposition being located in the spinodal region sufficiently long time at higher temperatures. Samples treated in the miscibility gap showed an agreement of the Si-rich binodal line with calculated phase diagrams. However, the Sn-rich binodal line stays undefined, perhaps due to grain boundary pinning of diffusing atoms. The study elucidates the possibility of tailoring the microstructure of magnesium silicide-stannide alloys utilizing merely judiciously designed heat treatment protocols. A particular attention is brought to spinodal decomposition, which has the potential to reduce the lattice thermal conductivity.
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| 6. |
- Su, R., et al.
(author)
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Rapid Synthesis of Porous, Mixed Phase Titania Films with Tailored Orientation of Rutile for Enhanced Photocatalytic Performance
- 2013
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In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:51, s. 27039-27046
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Journal article (peer-reviewed)abstract
- We report on a new, one-step electrochemical oxidation method for the rapid synthesis of mixed phase, polycrystalline TiO2 porous films with oriented rutile within a few minutes. The orientation as well as the surface chemical composition of rutile nanocrystallites can readily be tuned by adjusting the additive concentrations of HCl or HF in the electrolyte during synthesis. All TiO2 films show similar large specific surface area, which is ideal for the application of photocatalysis and photoelectrocatalysis. Compared to the random-oriented TiO2 film, films with an increasing portion of exposed rutile (101) facets were found to be characterized by enhanced photocatalytic oxidation and photoelectrochemical performances. We also observed a synergistic promotion effect of the orientation and surface F impurity. Most interesting, our tailor-oriented porous TiO2 films prepared using HF as additive show an impressive photocurrent generation at zero bias, which is similar to 50 times higher compared to that of the random-oriented TiO2 film.
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| 7. |
- Sun, Y., et al.
(author)
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Low-Cost High-Performance Zinc Antimonide Thin Films for Thermoelectric Applications
- 2012
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In: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 24:13, s. 1693-1696
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Journal article (peer-reviewed)abstract
- Zinc antimonide thin films with high thermoelectric performance are produced by a simple sputtering method. The phase-pure Zn4Sb3 and ZnSb thin films fulfill the key requirements for commercial TE power generation: cheap elements, cheap fabrication method, high performance and thermal stability. In addition, two completely new meta-stable crystalline phases of zinc antimonide have been discovered.
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| 8. |
- Örn Simonarson, Gunnar, 1986, et al.
(author)
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Evolution of the Polymorph Selectivity of Titania Formation under Acidic and Low-Temperature Conditions
- 2019
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In: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 4:3, s. 5750-5757
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Journal article (peer-reviewed)abstract
- Evolution of the polymorph selectivity of titanium dioxide was studied under acidic and low-temperature synthesis conditions. Short synthesis times resulted in high relative amounts of the rutile phase, and long synthesis times resulted in high relative amounts of the brookite and anatase phases. The effect of titania precursor concentration was investigated and found to have a large impact on the polymorph selectivity. As the reaction proceeds with time, changes in the chemical environment, caused in particular by the gradually decreasing titania precursor concentration, are therefore likely the cause of the change in polymorph selectivity observed.
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