To save content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about saving content to .
To save content items to your Kindle, first ensure email@example.com
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Cr-doped higher manganese silicides (HMSs) (Mn1-xCrx)Si1.75 (x = 0–0.35) have been prepared by repeated sintering from raw elemental powder using spark plasma sintering. The a- and cMn-axis length increases with increasing Cr content x. The results of powder X-ray diffraction and microstructural observation suggest that impurity phases, e.g. (Mn, Cr)Si and CrSi2, exist in the samples with x = 0.20 or above. The electrical resistivities and Seebeck coefficient decrease with increasing Cr content x. The Cr content x of 0.10 indicated the largest power factor at 850 K (1.39×10-3W/mK), followed in order by x of 0.25, 0, 0.05, 0.15, 0.20. To confirm the effect of Cr-doping on outputs of modules, two paired p-n modules consisting of n-type purchased Mg2Si and p-type Cr-doped HMS with x = 0, 0.05, 0.10, and 0.20 elements were prepared. The module consisting of (Mn0.9Cr0.1)Si1.75 showed the highest output, that is, 845 mW at 873 K on the hot side. There was approximately 8% improvement compared with that of the module consisting of Cr-free elements.
We applied NiSi2 as an electrode for thermoelectric modules because NiSi2 has high electric conductivity and is expected to suppress the inter-diffusion of Si from MgSi2 and higher manganese silicide (HMS). The thermal expansion coefficient of NiSi2 is close to that of Mg2Si but differs from that of HMS. Therefore, to reduce thermal stress, we tried to insert a buffer layer consisting of HMS and NiSi2 for the interface between the HMS sintered body and the NiSi2 electrode. The NiSi2 was prepared by using spark plasma sintering (SPS) equipment. NiSi2 electrodes and gradients were formed and connected with the HMS by SPS treatment. Crack-free bonding was achieved by inserting gradients consisting of HMS and NiSi2. The inserted composite buffer layer reduced interface stress and interface resistance between HMS and NiSi2.
The magnesium compound Mg2Si and its solid solutions are expected as n-type thermoelectric (TE) material because they are non-toxic, have a large Clarke number, and are light weight. In this study, we improved TE performance by doping Ge into Sb-doped Mg2Si to cause phonon scattering and increase carrier concentration. A bulk of Sb-doped Si-Ge alloy as the raw material was fabricated using an arc-melting method. A high-purity Mg2Si was synthesized from metal Mg and Sb-doped Si-Ge alloy using spark plasma sintering equipment. For the samples with the same Sb concentration, the electrical conductivity was equivalent. On the other hand, the Seebeck coefficient was dependent on Ge concentration. Due to phonon scattering, thermal conductivity decreased by a small amount of Ge doping and κph dominated for thermal conduction. The minimum thermal conductivity of Mg2Si0.90Ge0.10 was 2.25 W/mK (κph: 2.06 W/mK, κel: 0.19 W/mK). The dimensionless figure of merit (ZT) for the Mg2Si0.945Ge0.05Sb0.005 sample was higher than that of the others due to reducing thermal conductivity and increasing carrier concentration. The maximum ZT was 0.47 at 713 K.
In this study, we fabricated Mg2Si from metal Mg and Si with different particle sizes (425 - 300, 300 - 180, and 75 μm or less) using spark plasma sintering (SPS) equipment. Additionally, the Mg2Si formation was investigated. A sieved Si powder was mixed with metal Mg powder in an inert gas (Ar) atmosphere. The mixture was placed in a graphite die while still in an Ar atmosphere and subjected to SPS at 923 K and 1113 K. The obtained sintering bodies were Mg2Si particles with a size of about 5 μm. Then, the sintered bodies were evaluated by X-ray diffraction (XRD). As a result, it was confirmed that generation of Mg2Si increased with decreasing Si particle size.
Magnesium silicide (Mg2Si) has attracted much interest as an n-type thermoelectric material because it is eco-friendly, non-toxic, light, and relatively abundant compared with other thermoelectric materials. In this study, we tried to improve the thermoelectric performance by doping Sb and Ge in the Mg2Si, as well as further optimizing x in the carrier concentration to cause phonon scattering. A high purity Mg2Si was synthesized from metal Mg and Sb doped Si-Ge alloy by using spark plasma sintering (SPS) equipment. The sintered samples were cut and polished. They were evaluated by using X-ray diffraction (XRD) and X-ray fluorescence (XRF) analyses. The carrier concentration of the samples was measured by using Hall measurement equipment. The electrical conductivity and Seebeck coefficient were measured by using a standard four-probe method in a He atmosphere. The thermal conductivity was measured by using a laser-flash system. We succeeded in obtaining a Sb doped Mg2Si0.95Ge0.05 sintered body easily without any impurities with the SPS equipment. The electrical conductivity of the sample was increased, and thermal conductivity was decreased by increasing the amount of doped Sb. The dimensionless figure of merit ZT became 0.74 at 733 K in the Mg2Si0.95-xGe0.05Sbx sample with x = 0.0022.
NaxCoO2 has a particularly high contact resistance because it forms an insulated layer of NaHCO3 and Na2CO3, which are produced in a chemical reaction with carbon dioxide and water in air on the surface. In this study, we tried to improve the interface resistance between NaxCoO2 and Ag sheet electrodes by connecting these materials with the spark plasma sintering (SPS) technique. The interface resistance between NaxCoO2 and Ag sheet electrodes connected by SPS is compared with that connected with Ag paste. In an experiment, the interface resistance of a sample treated by decrease to less than 1/600 of the former value. It is thought that the NaHCO3 and Na2CO3 insulated layer is decomposed through the application of a large value of applied DC current by using the SPS technique.
Thermoelectric power generation has been attracting attention as a technology for waste heat utilization in which thermal energy is directly converted into electric energy. It is well known that layered cobalt oxide compounds such as NaCo2O4 and Ca3Co4O9 have high thermoelectric properties in p-type oxide semiconductors. However, in most cases, the thermoelectric properties in n-type oxide materials are not as high. Therefore, n-type magnesium silicide (Mg2Si) has been studied as an alternative due to its non-toxicity, environmental friendliness, lightweight property, and comparative abundance compared with other TE systems. In this study, we fabricated π-structure thermoelectric power generation devices using p-type NaCo2O4 elements and n-type Mg2Si elements. The p- and n-type sintering bodies were fabricated by spark plasma sintering (SPS). To reduce the resistance at the interface between elements and electrodes, we processed the surface of the elements before fabricating the devices. The end face of a Mg2Si element was covered with Ni by SPS and that of a NaCo2O4 element was coated with Ag by silver paste and soldering.
The thermoelectric device consisted of 18 pairs of p-type and n-type legs connected with Ag electrodes. The cross-sectional and thickness dimensions of the p-type elements were 3.0 mm × 5.0 mm × 7.6 mm (t) and those of the n-type elements were 3.0 mm × 3.0 mm × 7.6 mm (t). The open circuit voltage was 1.9 V and the maximum output power was 1.4 W at a heat source temperature of 873 K and a cooling water temperature of 283 K in air.
The thermoelectrical properties of α and γ phases of NaxCo2O4 having different amounts of Na were evaluated. The γ NaxCo2O4 samples were synthesized by thermal decomposition in a metal-citric acid compound, and the α NaxCo2O4 samples were synthesized by self-flux processing. Dense bulk ceramics were fabricated using spark plasma sintering (SPS), and the sintered samples were of high density and highly oriented. The thermoelectrical properties showed that γ NaxCo2O4 had higher electrical conductivity and lower thermal conductivity compared with α NaxCo2O4 and that α NaxCo2O4 had a larger Seebeck coefficient. These results show that γ NaxCo2O4 has a larger power factor and dimensionless figure of merit, ZT, than α NaxCo2O4.
Fast electrons are effectively generated from solid targets of
cone-geometry by irradiating intense laser pulses, which is applied to
fast ignition scheme. For realizing optimal core heating by those
electrons, understanding the characteristics of electrons emitted from
cone targets is crucial. In this paper, in order to understand the
generation and transport processes of hot electrons inside the cone
target, two-dimensional (2D) particle-in-cell (PIC) simulations were
carried out. It is shown that hot electrons form current layers which are
guided by self-generated surface magnetic field, which results in
effective energy transfer from laser pulse to hot electrons. When the hot
electrons propagate through the steep density gradient at the cone tip,
electrostatic field is induced via Weibel instability. As a result, hot
electrons are confined inside and emitted gradually from the target, as an
electron beam of long duration. Energy spectrum and temporal profile of
hot electrons are also evaluated at the rear side of the target, where the
profile of rear side plasma is taken from the fluid code and the result is
sent to Fokker-Planck code.
The reasons why the open circuit voltage (Voc) of high-x CuIn1-xGaxSe2 (CIGS)/ZnO solar cells remain low are discussed. Here it is shown that the Voc ceiling can be interpreted simply on the basis of a model that the valence-band energy (Ev) of CIGS is almost immovable irrespective of x. When the conduction-band energy (Ec) of ZnO is lower than that of high-x CIGS (DEc<0), the built-in potential (Vbi) of a CIGS/ZnO junction is equivalent to the flat-band potential (Vbi) that arises from the separation between the Fermi energies of the two materials. If the Ev (and therefore the Fermi energy) of p-type CIGS is constant with increasing x, the Vbi and Voc that follows the Vbi remain unchanged since the Fermi energy of ZnO is constant. This unchangeable Voc reduces the conversion efficiency of high-x CIGS cells in cooperation with reduced photocurrents due to a larger bandgap. A positive offset, ΔEc>o gives rise to a photoelectrons barrier in the conduction-band that partially cancels Voc, thus the Voc of a low-x CIGS cell is governed by the Ec of CIGS. Based upon this concept, a material selection guideline is given for the windows and transparent electrodes appropriate for high-x CIGS absorbers-based solar cells.
A transparent magnetic particle/organic film was synthesized from an iron–organic compound. Iron(III) 3-allylacetylacetonate (IAA) was polymerized followed by in situ hydrolysis yielding an iron oxide particle/oligomer hybrid. The sizes of magnetic particles were dependent upon the hydrolysis conditions of the IAA oligomers. A nanometer-sized ferrimagnetic iron oxide particle/oligomer hybrid showed a magnetization curve with no coercive force at 300 K and that with Hc of 200 Oe at 4.2 K, respectively. The magnetization versus H/T curves at 300 and 77 K were superimposed on each other and satisfied the Langevin equation. The transparent hybrid film showed a magnetization curve at room temperature. The absorption spectrum of the film was shifted to higher energy by 0.14 eV compared with that of bulk magnetite. The absorption edge of the film was blue-shifted.
A nanocrystalline magnetic particle/oligomer hybrid was successfully synthesized by polymerization of iron(III) 3-allylacetylacetonate (IAA) followed by in situ hydrolysis. An iron oxide particle/oligomer hybrid was synthesized by hydrolysis of the IAA oligomer under alkaline and reducing conditions by the addition of hydrazine or methylhydrazine. Crystalline particles of approximately 10 nm were found to be dispersed in the oligomeric matrix. The nanocrystalline particles were identified to be iron oxide spinel by x-ray diffraction analysis and electron diffraction. The nanometer-sized ferrimagnetic iron oxide particle/oligomer hybrid showed a typical superparamagnetic behavior.
A soft process for the intercalation of different ammonium cations into vanadium pentoxide was developed. By refluxing an aqueous solution containing ammonium , tetramethylammonium (CH3)4N+, and tetraethylammonium (C2H5)4N+ with V2O5 powders, intercalation compounds containing corresponding ammonium cations were obtained. The compound with aniline C6H5NH2 was also synthesized by the same process. The compounds with (CH3)4N+, (C2H5)4N+, and also C6H5NH2 had diffraction patterns consisting of very sharp 00l lines. The spacing for sandwiching the intercalates (the identity period), (CH3)4N+, (C2H5)4N+, and C6H5NH2, was 1.29, 1.31, and 1.39 nm, respectively.
A nanocrystalline α–Fe2O3 particle/oligomer hybrid can be synthesized by polymerization of iron (III) 3-allylacetylacetonate (IAA) followed by in situ hydrolysis. The polymerization of IAA was dependent upon the polymerization temperature and solvent. GPC measurement showed that the polymerization degree of the IAA oligomer ranged from ∼3 to ∼6. The magnetic particle/oligomer hybrid was synthesized by hydrolysis of the IAA oligomer under a neutral or alkaline condition. Crystalline particles from 10 to 40 nm were finely dispersed in the oligomeric matrix, depending upon the hydrolysis conditions. The nanocrystalline particles below 10 nm in diameter were identified to be α−Fe2O3 by electron diffraction. The nanosized α−Fe2O3/oligomer hybrid was found to show superparamagnetic behavior.
Email your librarian or administrator to recommend adding this to your organisation's collection.