| 1. |
- Eremina, R. M., et al.
(författare)
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Magnetization and specific heat of the dimer system CuTe(2)O(5)
- 2011
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Ingår i: European Physical Journal B. - : Springer Science and Business Media LLC. - 1434-6028 .- 1434-6036. ; 84:3, s. 391-395
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Tidskriftsartikel (refereegranskat)abstract
- We report on magnetization and specific heat measurements on single-crystalline CuTe(2)O(5). The experimental data are directly compared to theoretical results for two different spin structures, namely an alternating spin-chain and a two-dimensional (2D) coupled dimer model, obtained by Das et al. [Phys. Rev. B 77, 224437 (2008)]. While the analysis of the specific heat does not allow to distinguish between the two models, the magnetization data is in good agreement with the 2D coupled dimer model.
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| 2. |
- 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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| 3. |
- Scott, E. A. S., et al.
(författare)
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Bi2CoO2F4─A Polar, Ferrimagnetic Aurivillius Oxide-Fluoride
- 2022
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 34:21, s. 9775-9785
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Tidskriftsartikel (refereegranskat)abstract
- Aurivillius oxides have been a research focus due to their ferroelectric properties, but by replacing oxide ions by fluoride, divalent magnetic cations can be introduced, giving Bi2MO2F4(M = Fe, Co, and Ni). Our combined experimental and computational study on Bi2CoO2F4 indicates a low-temperature polar structure of P21ab symmetry (analogous to ferroelectric Bi2WO6) and a ferrimagnetic ground state. These results highlight the potential of Aurivillius oxide-fluorides for multiferroic properties. Our research has also revealed some challenges associated with the reduced tendency for polar displacements in the more ionic fluoride-based systems.
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| 4. |
- Dahl, P., et al.
(författare)
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Densification and properties of zirconia prepared by three different sintering techniques
- 2007
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Ingår i: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 33:8, s. 1603-1610
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Tidskriftsartikel (refereegranskat)abstract
- Densification of nanocrystalline yttria stabilized zirconia (YSZ) powder with 8 mol% Y2O3, prepared by a glycine/nitrate smoldering combustion method, was investigated by spark plasma sintering, hot pressing and conventional sintering. The spark plasma sintering technique was shown to be superior to the other methods giving dense materials (>= 96%) with uniform morphology at lower temperatures and shorter sintering time. The grain size of the materials was 0.21, 0.37 and 12 mu m after spark plasma sintering, hot pressing and conventional sintering, respectively. Total electrical conductivity of the materials showed no clear correlation with the grain size, but the activation energy for spark plasma sintered materials was slightly higher than for materials prepared by the two other densification methods. The hardness, measured by the Vickers indentation method, was found to be independent on grain size while fracture toughness, derived by the indentation method, was slightly decreasing with increasing grain size.
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| 5. |
- Eldesouky, A., et al.
(författare)
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Effect of grain size reduction of AA2124 aluminum alloy powder compacted by spark plasma sintering
- 2014
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 609, s. 215-221
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Tidskriftsartikel (refereegranskat)abstract
- Nanocrystalline (Average grain size similar to 200 nm) bulk AA2124 alloy was produced through high energy ball milling of microcrystalline powder followed by spark plasma sintering (SPS) at 480 degrees C with a holding time of 10 min. The effect of initial particle and grain size on the microstructural evolution as well as on the relative density and mechanical properties of the specimens consolidated through SPS and hot pressing (HP) at the same temperature for 60 min was investigated for ball milled nano-powders (NP), as well as as-received micro-powders (MP). Results showed that the NP specimens consolidated with SPS had the highest microhardness values compared to the other specimens despite not achieving full densification. On the other hand, a general increase in density, hardness, and compressive strength was observed for all SPS consolidates compared to HP. The presence of aluminum oxide and its influence on the consolidation process as well as the resulting mechanical properties of the bulk specimens is also discussed. (C) 2014 The Authors. Published by Elsevier B.V.
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| 6. |
- Fiameni, S., et al.
(författare)
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Effect of Synthesis and Sintering Conditions on the Thermoelectric Properties of n-Doped Mg2Si
- 2014
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 43:6, s. 2301-2306
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Tidskriftsartikel (refereegranskat)abstract
- Magnesium silicide (Mg2Si)-based alloys are promising candidates for thermoelectric (TE) energy conversion in the middle-high temperature range. The detrimental effect of the presence of MgO on the TE properties of Mg2Si based materials is widely known. For this reason, the conditions used for synthesis and sintering were optimized to limit oxygen contamination. The effect of Bi doping on the TE performance of dense Mg2Si materials was also investigated. Synthesis was performed by ball milling in an inert atmosphere starting from commercial Mg2Si powder and Bi powder. The samples were consolidated, by spark plasma sintering, to a density > 95%. The morphology, and the composition and crystal structure of samples were characterized by field-emission scanning electronic microscopy and x-ray diffraction, respectively. Moreover, determination of Seebeck coefficients and measurement of electrical and thermal conductivity were performed for all the samples. Mg2Si with 0.1 mol% Bi doping had a ZT value of 0.81, indicative of the potential of this method for fabrication of n-type bulk material with good TE performance.
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| 7. |
- 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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| 8. |
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| 9. |
- Laurita, N. J., et al.
(författare)
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Singlet-Triplet Excitations and Long-Range Entanglement in the Spin-Orbital Liquid Candidate FeSc2S4
- 2015
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 114:20
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical models of the spin-orbital liquid (SOL) FeSc2S4 have predicted it to be in close proximity to a quantum critical point separating a spin-orbital liquid phase from a long-range ordered magnetic phase. Here, we examine the magnetic excitations of FeSc2S4 through time-domain terahertz spectroscopy under an applied magnetic field. At low temperatures an excitation emerges that we attribute to a singlet-triplet excitation from the SOL ground state. A threefold splitting of this excitation is observed as a function of applied magnetic field. As singlet-triplet excitations are typically not allowed in pure spin systems, our results demonstrate the entangled spin and orbital character of singlet ground and triplet excited states. Using experimentally obtained parameters we compare to existing theoretical models to determine FeSc2S4's proximity to the quantum critical point. In the context of these models, we estimate the characteristic length of the singlet correlations to be xi / (a/2) approximate to 8.2 (where a/2 is the nearest neighbor lattice constant), which establishes FeSc2S4 as a SOL with long-range entanglement.
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| 10. |
- 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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