| 1. |
- Battiston, S., et al.
(författare)
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Synthesis and Characterization of Al-Doped Mg2Si Thermoelectric Materials
- 2013
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Ingår i: Journal of Electronic Materials. - New York : Springer. - 0361-5235 .- 1543-186X. ; 42:7, s. 1956-1959
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Tidskriftsartikel (refereegranskat)abstract
- Magnesium silicide (Mg2Si)-based alloys are promising candidates for thermoelectric (TE) energy conversion for the middle to high range of temperature. These materials are very attractive for TE research because of the abundance of their constituent elements in the Earth's crust. Mg2Si could replace lead-based TE materials, due to its low cost, nontoxicity, and low density. In this work, the role of aluminum doping (Mg2Si:Al = 1:x for x = 0.005, 0.01, 0.02, and 0.04 molar ratio) in dense Mg2Si materials was investigated. The synthesis process was performed by planetary milling under inert atmosphere starting from commercial Mg2Si pieces and Al powder. After ball milling, the samples were sintered by means of spark plasma sintering to density > 95%. The morphology, composition, and crystal structure of the samples were characterized by field-emission scanning electron microscopy, energy-dispersive spectroscopy, and x-ray diffraction analyses. Moreover, Seebeck coefficient analyses, as well as electrical and thermal conductivity measurements were performed for all samples up to 600A degrees C. The resultant estimated ZT values are comparable to those reported in the literature for these materials. In particular, the maximum ZT achieved was 0.50 for the x = 0.01 Al-doped sample at 600A degrees C.
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| 2. |
- Fiameni, S., et al.
(författare)
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Introduction of Metal Oxides into Mg2Si Thermoelectric Materials by Spark Plasma Sintering
- 2013
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Ingår i: Journal of Electronic Materials. - New York : Springer. - 0361-5235 .- 1543-186X. ; 42:7, s. 2062-2066
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Tidskriftsartikel (refereegranskat)abstract
- Oxide incorporation into thermoelectric Mg2Si-based materials was performed starting from commercial Mg2Si and commercial metal oxides by applying ball milling and spark plasma sintering (SPS) processing. The SPS conditions, such as sintering temperature, pressure, and holding time, were optimized with the aim of obtaining both full densification and oxide incorporation. Thermoelectric characterizations, such as Seebeck coefficient and electrical and thermal conductivity, were carried out and related to the pellet compositions. The morphology, composition, and crystallographic structure of the samples were characterized by field-emission scanning electron microscopy, energy-dispersive spectrometry, and x-ray diffraction analyses, respectively.
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| 3. |
- Saleemi, Mohsin, et al.
(författare)
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Evaluation of the Structure and Transport Properties of Nanostructured Antimony Telluride (Sb2Te3)
- 2014
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 43:6, s. 1927-1932
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Tidskriftsartikel (refereegranskat)abstract
- Antimony telluride, (Sb2Te3), and its doped derivatives are considered to be among the best p-type thermoelectric (TE) materials for room temperature (300-400 K) applications. However, it is still desirable to develop rapid and economical routes for large-scale synthesis of Sb2Te3 nanostructures. We report herein a high yield, simple and easily scalable synthetic method for polycrystalline Sb2Te3 nanostructures. Prepared samples were compacted into dense pellets by use of spark plasma sintering. The products were characterized by x-ray diffraction and scanning electron microscopy. To investigate the anisotropic behavior of Sb2Te3 TE transport property measurements were performed along and perpendicular to the direction of compaction. Thermal conductivity, electrical conductivity, and Seebeck coefficient measurement over the temperature range 350-525 K showed that the anisotropy of the material had a large effect on TE performance.
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| 4. |
- Saleemi, Mohsin, et al.
(författare)
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Spark plasma sintering and thermoelectric evaluation of nanocrystalline magnesium silicide (Mg2Si)
- 2013
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Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 48:5, s. 1940-1946
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Tidskriftsartikel (refereegranskat)abstract
- Recently magnesium silicide (Mg2Si) has received great interest from thermoelectric (TE) society because of its non-toxicity, environmental friendliness, comparatively high abundance, and low production material cost as compared to other TE systems. It also exhibited promising transport properties, including high electrical conductivity and low thermal conductivity, which improved the overall TE performance (ZT). In this work, Mg2Si powder was obtained through high energy ball milling under inert atmosphere, starting from commercial magnesium silicide pieces (99.99 %, Alfa Aesar). To maintain fine microstructure of the powder, spark plasma sintering (SPS) process has been used for consolidation. The Mg2Si powder was filled in a graphite die to perform SPS and the influence of process parameters as temperature, heating rate, holding time and applied pressure on the microstructure, and densification of compacts were studied in detail. The aim of this study is to optimize SPS consolidation parameters for Mg2Si powder to achieve high density of compacts while maintaining the nanostructure. X-Ray diffraction (XRD) was utilized to investigate the crystalline phase of compacted samples and scanning and transmission electron microscopy (SEM & TEM) coupled with Energy-Dispersive X-ray Analysis (EDX) was used to evaluate the detailed microstructural and chemical composition, respectively. All sintered samples showed compaction density up to 98 %. Temperature dependent TE characteristics of SPS compacted Mg2Si as thermal conductivity, electrical resistivity, and Seebeck coefficient were measured over the temperature range of RT 600 A degrees C for samples processed at 750 A degrees C, reaching a final ZT of 0.14 at 600 A degrees C.
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| 5. |
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| 6. |
- Stingaciu, Marian, et al.
(författare)
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Magnetoresistivity in CoFe(2)O(4)-BaTiO(3) composites produced by spark plasma sintering
- 2011
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 110:4, s. 044903-
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Tidskriftsartikel (refereegranskat)abstract
- Ceramic composites of (CoFe(2)O(4))(x)-(BaTiO(3))((1-x)) with x = 0.20, 0.25, and 0.30 have been synthesized by spark plasma sintering at 1000 degrees C under a uniaxial pressure of 75 MPa using commercially available nanopowders as starting materials. The composites reveal a negative magnetoresistivity effect of about -1% at room temperature. An enhancement was observed at lower temperatures, and an effect of -4.1% was found in the composite with x 0.30 at 150 K by applying an external magnetic field of 25 kOe. The temperature dependence of the resistivity indicates variable range hopping involved in charge transport.
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| 7. |
- Stingaciu, Marian, et al.
(författare)
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The magnetodielectric effect in BaTiO3-SrFe12O19 nanocomposites
- 2014
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Ingår i: Journal of Materials Chemistry C: Materials for Optical and Electronic Devices. - : Royal Society of Chemistry (RSC). - 2050-7526. ; 2:2, s. 325-330
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Tidskriftsartikel (refereegranskat)abstract
- A nanoscale composite consisting of 30 vol% magnetic strontium hexaferrite SrFe12O19 embedded in a high dielectric permittivity matrix of BaTiO3 has been produced by the spark plasma sintering method. The morphology and phase composition were characterized by transmission electron microscopy (TEM) and powder X-ray diffraction (XRD) techniques. TEM micrographs indicate that no considerable grain growth occurs and different strained regions were formed by the sintering process. XRD investigations show no evidence of a chemical reaction between the constituents. The dielectric properties of such a nanocomposite were investigated versus temperature (50-300 K), frequency (100 Hz to 100 kHz) and magnetic field (0-5.6 Tesla). A magnetodielectric (MD) effect was detected in the whole studied temperature range. Above 150 K the occurrence of sharp magnetodielectric resonances around 1 kHz leads to a considerable enhancement of the effect. At temperatures below 150 K a positive MD effect was detected which is independent of the frequency.
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| 8. |
- Sutka, A., et al.
(författare)
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An alternative method to modify the sensitivity of p-type NiFe2O4 gas sensor
- 2012
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Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 47:6, s. 2856-2863
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Tidskriftsartikel (refereegranskat)abstract
- Our objective was to determine the role of cooling rate on gas-sensing properties of annealed nano-grained nickel ferrite (NiFe2O4). The sol-gel auto combustion method was used for the preparation of NiFe2O4. To estimate structural and microstructural features, X-ray diffraction, and scanning electron microscopy techniques were used. For gas-sensing measurements different volatile organic compounds (VOCs) were used as testing gases. To identify the contribution of the different sensing layer elements to the conduction, ac impedance spectroscopy (IS) measurements were performed. It was found that the sensors cooled with lower rate exhibited better sensing performance, due to increase of resistance. Overall, this article covers an alternative method for modifying nickel ferrite gas sensor sensitivity.
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| 9. |
- Zayed, M. E., et al.
(författare)
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Temperature dependence of the pressure induced monoclinic distortion in the spin S=1/2 Shastry-Sutherland compound SrCu2(BO3)(2)
- 2014
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Ingår i: Solid State Communications. - : Elsevier BV. - 0038-1098 .- 1879-2766. ; 186, s. 13-17
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the monoclinic distortion that occurs at 4.7 GPa at room temperature in the frustrated Shastry-Sutherland model quantum magnet SrCu2(BO3)(2) as a function of pressure and temperature by means of powder and single crystal angle dispersive synchrotron X-ray diffraction. Our results indicate that the onset of the structural distortion varies in a narrow pressure range between 4.0 and 5.0 GPa. This result will be useful in order to distinguish between magnetic transitions related to structural changes and potential intrinsic quantum phase transitions that various reports have suggested to take place in SrCu2(BO3)(2) at high pressure and low temperature.
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