Improved microstructure and thermoelectric properties of higher manganese silicide processed by reactive spark plasma sintering (original) (raw)
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Journal of Nanoscience and Nanotechnology, 2017
Higher manganese silicides (HMS), represented by MnSi x x = 1.71-1.75), are promising p-type candidates for thermoelectric (TE) energy harvesting systems at intermediate temperature range. The materials are very attractive as they may replace lead based compounds due to their nontoxicity, low cost of starting materials, and high thermal and chemical stability. Dense pellets were obtained through fast reactive sintering by spark plasma sintering (SPS). The addition-or nanoinclusion, of Al and Mg permitted the figure of merit enhancement of the material obtained with this technique, reaching the highest value of 0.40 at 600 C. Morphology, composition and crystal structure of the samples were characterized by electron microscopies, energy dispersive X-ray spectroscopy, and X-ray diffraction analyses, respectively.
Journal of Alloys and Compounds, 2022
Higher manganese silicide (HMS) MnSi γ films with varying γ (1.65 ≤ γ ≤ 3.23) were deposited on oxidized Si wafers at 703K by radio frequency (RF) magnetron co-sputtering of Mn and Si targets. As-deposited films were annealed at 1273K for 3min using a lamp annealing system, and the thermoelectric (TE) properties were measured in the temperature range from room temperature to 1073K. All the MnSi γ films were p-type below about 550K, but the polarity converted to n-type at higher temperatures. Moreover, the power factor (PF) of the polarity-inverted films was exceptionally high, reaching the maximum value of 12.3 mW/K 2 m in the annealed MnSi 2.04 film. In case of the as-deposited films, the PF in the p-type regime (PF p) grew larger as the Si/Mn molar ratio γ approached the stoichiometric value of 1.73, while the PF n became vanishingly small. In contrast, the PF n of the annealed films remained very high even in the Mn-rich film (γ < 1.73), such that 9.6 mW/K 2 m was obtained from the MnSi 1.65 film. Hall measurement at elevated temperatures (≤ 773K) showed that electron mobility was greatly increased after the annealing, which has produced unusually high PF n. The HMS phase was composed of Mn 4 Si 7 and Mn 11 Si 19 , but regions of unidentified phase were also confirmed by transmission Kikuchi diffraction (TKD) analysis, the proportion of which was larger in the Si-rich films. The modification of the band structure induced by defects and structural disorder of the Mn and/or Si sublattice are supposed to be the origin of this novel phenomenon.
Journal of Alloys and Compounds, 2019
Effects of Re substitution for Mn on the microstructure-property relationships in Mn 30.4 Re 6.0 Si 63.6 thermoelectric material have been investigated in comparison with those in Mn 36.4 Si 63.6. The rapid quenching using the meld spinning leads to relatively uniform distribution of Re. After sintering, the Nowotny chimney ladder phases known as the higher manganese silicide (HMS) are stabilized in both the Re-free and Re-substituted HMSs, and the chemical formulae become Mn 15 Si 26 and Mn 19 Si 33 , respectively. The Re atoms are successfully substituted for Mn in the (Mn,Re) 19 Si 33 HMS. The number density of the sublattice dislocation in the Re-substituted HMS is 1.6 times higher than that in the Re-free HMS, that causes a decrease in lattice thermal conductivity. Due to the impurity effect of the Re substitution, the electrical conductivity is supposed to be enhanced, resulting in the highest dimensionless figure of merit (ZT) among the investigated HMSs.
Thermoelectric Properties of Higher Manganese Silicide Consolidated by Flash-Sintering Technique
Social Science Research Network, 2022
Higher manganese silicide (HMS) MnSi γ films with varying γ (1.65 ≤ γ ≤ 3.23) were deposited on oxidized Si wafers at 703K by radio frequency (RF) magnetron co-sputtering of Mn and Si targets. As-deposited films were annealed at 1273K for 3min using a lamp annealing system, and the thermoelectric (TE) properties were measured in the temperature range from room temperature to 1073K. All the MnSi γ films were p-type below about 550K, but the polarity converted to n-type at higher temperatures. Moreover, the power factor (PF) of the polarity-inverted films was exceptionally high, reaching the maximum value of 12.3 mW/K 2 m in the annealed MnSi 2.04 film. In case of the as-deposited films, the PF in the p-type regime (PF p) grew larger as the Si/Mn molar ratio γ approached the stoichiometric value of 1.73, while the PF n became vanishingly small. In contrast, the PF n of the annealed films remained very high even in the Mn-rich film (γ < 1.73), such that 9.6 mW/K 2 m was obtained from the MnSi 1.65 film. Hall measurement at elevated temperatures (≤ 773K) showed that electron mobility was greatly increased after the annealing, which has produced unusually high PF n. The HMS phase was composed of Mn 4 Si 7 and Mn 11 Si 19 , but regions of unidentified phase were also confirmed by transmission Kikuchi diffraction (TKD) analysis, the proportion of which was larger in the Si-rich films. The modification of the band structure induced by defects and structural disorder of the Mn and/or Si sublattice are supposed to be the origin of this novel phenomenon.
Ceramics International, 2021
Higher manganese silicides (HMS) are promising alternative materials for middle to high temperature thermoelectric applications as a low-cost, non-toxic and highly stable p-type leg. Many of the preparation methods that have been reported previously require long-time and energy consuming processes, as well as expensive equipment, and often do not result in a material of sufficient quality. In this study, the simple, cost-effective and eco-friendly technique of pack cementation is applied. HMS powders synthesized at different experimental conditions are studied and compared considering their structure, composition, short-term thermal stability in air and thermoelectric properties. X-ray diffraction analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, thermogravimetry and thermoelectric measurements (in terms of Seebeck coefficient, electrical and thermal conductivity) were employed for the characterization of the material and evaluation of its performance. All samples were identified as HMS and only some negligible traces of MnSi were detected. They moderately oxidize when heated non-isothermally under air atmosphere up to 1473 K, while the presence of HMS remains dominant even at such high temperatures. Their thermoelectric properties were remarkable for an undoped material, with a maximum figure of merit (ZT) of 0.47 at 777 K. Pack cementation appeared to have a great potential as the synthesis route of high-efficiency HMS.
Journal of Alloys and Compounds, 2015
A polycrystalline higher manganese silicide (HMS) material has been sintered from an aluminiumenriched gas-phase atomized powder using spark plasma sintering (SPS). After tailoring the SPS parameters, the polycrystal is almost fully dense, mainly constituted by the Mn 15 Si 26 HMS phase and the average grain size is around 10 lm. Transmission electron microscopy investigations coupled to energy dispersive X-ray spectroscopy (EDS) measurements show that: (i) alumina is segregated at grain boundaries and multiple points; (ii) a small amount of residual silicon is homogeneously distributed in the sintered microstructure; (iii) intragranular nanometre-sized inclusions (averaged diameter around 20 nm, concentration of 8.9 Â 10 À4 inclusions/nm 2) are observed in most of the individual grains constituting the polycrystal. Some are crystalline and made of metallic MnSi, some are residual holes/gas bubbles entrapped into the sintered microstructure during the manufacturing step; (iv) each individual grain contains around 1 at.% of aluminium that is dispersed in the Mn 15 Si 26 elemental lattice and then acts possibly as a dopant. Thermoelectrical properties of the sintered material have been investigated in the 20-700°C temperature range and compared to the literature. The material exhibits the desired P-type conduction, the Seebeck coefficient has a high value for all the temperature range and in the same time the thermal conductivity is especially low. It is postulated that aluminium doping and the presence of nanometresized inclusions in the sintered microstructure are responsible for the dimensionless figure of merit (ZT) around 0.7 measured at 500°C. Such a value, obtained on a sample manufactured with a very simple process, is the best one ever reported for this kind of material.
Spark plasma sintering and thermoelectric evaluation of nanocrystalline magnesium silicide (Mg2Si)
Journal of Materials Science, 2013
Recently magnesium silicide (Mg 2 Si) 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, Mg 2 Si 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 Mg 2 Si 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 Mg 2 Si 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 Mg 2 Si as thermal conductivity, electrical resistivity, and Seebeck coefficient were measured over the temperature range of RT 600°C for samples processed at 750°C, reaching a final ZT of 0.14 at 600°C.
Thermoelectric performance of higher manganese silicide nanocomposites
Journal of Alloys and Compounds, 2015
Thermoelectric is a promising technology that can convert temperature differences to electricity (or vice versa). However, their relatively low efficiencies limit their applications to thermoelectric power generation systems. Therefore, low cost and high performance are important prerequisites for the application of thermoelectric materials to automotive thermoelectric generators. Silicide-based thermoelectric materials are good candidates for such applications. Recently, the thermoelectric performances of silicide-based thermoelectric materials have been significantly improved. However, increasing the thermoelectric performance of the materials while ensuring mechanical reliability remains a challenge. This review summarizes the preparation and design guidelines for silicide-based thermoelectric nanocomposites, as well as our recent progress in the development of nanocomposites with high thermoelectric performances or high mechanical reliabilities.
Introduction of Metal Oxides into Mg2Si Thermoelectric Materials by Spark Plasma Sintering
Journal of Electronic Materials, 2013
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Materials Letters
Complex geometry legs were advantageous to obtain higher thermoelectric potential due to a better thermal dissipation. Among all industrial processes, additive manufacturing using a selective laser sintering (SLS) or melting (SLM) techniques is the most promising to obtain such complex-shape legs without machining step. In this work, for the first time, Higher Manganese Silicide (HMS) sheet samples were synthetized, sintered and shaped simultaneously by additive manufacturing from ball milled manganese and silicon powder. Impact of surface power density and scanning rate of the laser on the microstructural and structural properties was discussed for some SLS/M parameters. Characterizations have shown that both densification and pure HMS phase can be obtained by SLS/M.