Journal of the Japan Society of Powder and Powder Metallurgy
Online ISSN : 1880-9014
Print ISSN : 0532-8799
ISSN-L : 0532-8799
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Volume 57, Issue 4
April
Displaying 1-15 of 15 articles from this issue
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Paper
Paper
  • Crystal and Electronic Structures of Bi4(Ti, Si)3O12 Ferroelectrics
    Yasushi Idemoto, Hirotaka Kotani, Naoto Kitamura
    2010 Volume 57 Issue 4 Pages 191-197
    Published: 2010
    Released on J-STAGE: July 06, 2010
    DOIhttps://doi.org/10.2497/jjspm.57.191
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    In this work, we synthesized Bi4Ti3O12 and Bi4Ti2.85Si0.15O12 by means of a conventional solid-state reaction, and investigated their ferroelectric properties. From P-E hysteresis measurement, it was demonstrated that the Bi4Ti3O12 began to show higher remanent polarization and lower coercive field by partially substituting Si for Ti. In order to clarify how the substitution affected the crystal and electronic structures and thus ferroelectric properties, we performed X-ray absorption fine structure spectroscopy, synchrotron X-ray diffraction and neutron diffraction measurements. As a result, it was found by Rietveld analysis using neutron diffractions that local distortions of TiO6 octahedra increased by the partial substitution of Si for Ti. Taking it into account that such a distortion induces a polarization in a crystal, this may be one of the reasons why the substitution improved ferroelectric properties of Bi4Ti3O12. From electronic density distributions estimated by maximum entropy method, it was also suggested that Ti-O bond became stronger by the substitution.
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Special Issue: New Development of Thermoelectric Materials — Aiming for Higher Performance —
Summarization
Review
  • Development of Thermoelectric Materials Based on Heusler Compounds for Energy Harvesting Applications
    Yoichi Nishino
    2010 Volume 57 Issue 4 Pages 201-206
    Published: 2010
    Released on J-STAGE: July 06, 2010
    DOIhttps://doi.org/10.2497/jjspm.57.201
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    The Heusler-type Fe2VAl compound is found to be a nonmagnetic semimetal with a sharp pseudogap at the Fermi level. Remarkably, doping of quaternary elements causes a significant decrease in the electrical resistivity and a large enhancement in the Seebeck coefficient. Since the Seebeck coefficient varies systematically with the valence electron concentration (VEC), irrespective of doping elements, the net effect of doping is most likely to cause a rigid-band-like shift of the Fermi level from the central region in the pseudogap. The Fe2VAl-based compounds are a promising candidate for thermoelectric power generation because of the possession of higher thermoelectric power factor than that of Bi-Te system. The durable thermoelectric module designed for motorcycles has successfully been fabricated, using microstructural Fe2VAl-based sintered alloys prepared by mechanical alloying and pulse-current sintering.
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Paper
  • Off-stoichiometric Effects on Thermoelectric Properties of Fe2VAl-based Compounds
    Yusuke Sandaiji, Naoki Ide, Yoichi Nishino, Takeshi Ohwada, Shota Hara ...
    2010 Volume 57 Issue 4 Pages 207-212
    Published: 2010
    Released on J-STAGE: July 06, 2010
    DOIhttps://doi.org/10.2497/jjspm.57.207
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    We report on the thermoelectric properties of Fe2-x(V1+x-yTiy)Al alloys (−0.04≤x≤0.02, 0≤y≤0.10). While a small deviation from the stoichiometric Fe2VAl composition causes an enhancement in the Seebeck coefficient, a slight substitution of Ti for V leads to a further increase in the Seebeck coefficient and a decrease in the electrical resistivity. The Seebeck coefficient reaches 110 μV/K at 300 K for x=−0.04 and y=0.03, which is the largest in the p-type Fe2VAl-based alloys so far reported. The electronic structures of Fe2-xV1+xAl alloys with x=−0.04, 0 and 0.02 have been investigated by soft X-ray photoelectron spectroscopy. The valence-band spectra near the EF of Fe-rich alloy (x=−0.04) is drastically changed from that of the stoichiometric Fe2VAl. Therefore substantial enhancements in the Seebeck coefficient for the off-stoichiometric alloys could be due to a modification in the band structure on the valence band side around the Fermi level EF.
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  • Soft X-ray Photoelectron Spectroscopy of Heusler-type Thermoelectric Alloys Fe2-x-yIryV1+xAl
    Shota Harada, Takeshi Ohwada, Manabu Inukai, Masahiko Kato, Shinya Yag ...
    2010 Volume 57 Issue 4 Pages 213-217
    Published: 2010
    Released on J-STAGE: July 06, 2010
    DOIhttps://doi.org/10.2497/jjspm.57.213
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    The valence-band and core-level electronic structures of Heusler-type alloys Fe2-x-yIryV1+xAl have been investigated by soft X-ray photoelectron spectroscopy, which shows that the valence-band structure near the Fermi level EF is drastically altered by the off-stoichiometric concentration change x, while the position of EF is moderately tuned by the Ir substitution y in a rigid-band-like manner. These changes in the electronic structure lead to the remarkable enhancement of their thermoelectric power. For x > 0, the V 2p core level spectra also show the appearance of new chemically shifted components in the low binding energy side of the main line, which may be attributed mainly to the excess V occupying the Fe site (the anti-site V) as well as V in the surface layer. The present results suggest that the drastic and moderate changes in the electronic structure may be caused by the emergence of such anti-site defects in the off-stoichiometric Fe and V concentrations and by the common band formation between the Fe 3d bands and the substituted Ir 5d states, respectively.
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  • Effect of Transition Element Substitution on the p-type Thermoelectric Properties of ZrNiSn-based Half-Heusler Compounds
    Toshihiro Kamiya, Yoichi Nishino
    2010 Volume 57 Issue 4 Pages 218-223
    Published: 2010
    Released on J-STAGE: July 06, 2010
    DOIhttps://doi.org/10.2497/jjspm.57.218
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    We report on the electrical resistivity and the Seebeck coefficient for the p-type half-Heusler compounds ZrNi1-xMxSn with M=Co, Rh and Ir, and x=0-0.30, in addition to the doping effect on the thermal conductivity at 300 K. While a slight substitution of Ir causes a significant decrease in the electrical resistivity at 300 K, the Co doping results in a large enhancement in the Seebeck coefficient, reaching 170 μV/K at 300 K for x=0.05. The net effect of doping is most likely to cause a modification in the band structure around the band gap. Although the thermal conductivity remains in the range of 6-7 W/mK for the Co substitution, it decreases more rapidly for the Ir substitution, reaching 2.6 W/mK at x=0.2. Further doping of heavier atoms like Hf for the Co substitution reduces more effectively the lattice thermal conductivity while retaining the low electrical resistivity as well as the large Seebeck coefficient, so that the thermal conductivity for Zr0.5Hf0.5Ni0.85Co0.15Sn is as low as 3.8 W/mK, in spite of the possession of a large power factor of the order of 10-3 W/mK2 at 800 K.
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Memorial Lecture of JSPM Award
  • Microstructural Control and Development of Synthesis Route for Enhancing Performance of Sintered Thermoelectric Oxide Polycrystals via Chemical Solution Process
    Mikio Ito, Tomoya Nagira, Shigeru Katsuyama
    2010 Volume 57 Issue 4 Pages 224-231
    Published: 2010
    Released on J-STAGE: July 06, 2010
    DOIhttps://doi.org/10.2497/jjspm.57.224
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    The thermoelectric oxides, such as a p-type NaxCo2O4 and an n-type SrTiO3 etc., have been synthesized by the chemical solution process. The polymerized complex (PC) process efficiently develops compositional homogeneity of sintered polycrystals and promotes substitution of a doping element. In the case of NaxCo2O4 with a layered crystal structure, a plate-like powder precursor can be synthesized by the citric acid complex process, providing a sintered polycrystal with c-axis oriented crystallographic anisotropy. The establishment of rapid synthesis process at a low temperature of the n-type SrTiO3 system was tried by using the PC process and the pulsed current heating (PCH) method. TiB2 addition was found to be quite effective not only for reduction in the electrical resistivity, but also for rapid densification during the sintering. As a result, it was clarified that the synthesis route via the PC process, the PCH method and TiB2 addition is quite promising as a rapid synthesis process at a low temperature of the SrTiO3 system. Based on the experimental results obtained in this study, the chemical solution process is considered to be a quite effective methodology for enhancing performances of structural and functional oxides and for developing the synthesis process under soft conditions.
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Review
  • Thermoelectric Properties of SrTiO3: Bulks, Superlattices, and Transistors
    Hiromichi Ohta
    2010 Volume 57 Issue 4 Pages 232-236
    Published: 2010
    Released on J-STAGE: July 06, 2010
    DOIhttps://doi.org/10.2497/jjspm.57.232
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    Here I review the thermoelectric properties of electron doped SrTiO3. Since density of states effective mass of electron carrier in SrTiO3 crystal is rather large, heavily electron doped SrTiO3 crystal exhibits rather large Seebeck coefficient (S). The reliable thermoelectric figure of merit, ZT is ∼0.08 at room temperature and ∼0.3 at 1,000 K, which is highest among metallic oxides. Recently, we found that high-density (∼1021 cm-3) two-dimensional (2D) electron layers in SrTiO3 crystal exhibits giant S, which is ∼5 times larger than that of simple bulk, when the layer thickness is as thin as one unit cell (0.3905 nm). The 2D electron layer is realized by superlattices of SrTiO3/SrTi0.8Nb0.2O3 or TiO2/SrTiO3 heterointerface. Very recently, we fabricated high performance field effect transistors (FETs) on SrTiO3 single crystal to modulate the Seebeck coefficient by applying the gate voltage.
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Paper
  • Thermoelectric Property of Sr and Cu Substituted Ca3Co4O9+δ
    Naoya Kamigaito, Kenji Kamishima, Koichi Kakizaki, Nobuyuki Hiratsuka
    2010 Volume 57 Issue 4 Pages 237-241
    Published: 2010
    Released on J-STAGE: July 06, 2010
    DOIhttps://doi.org/10.2497/jjspm.57.237
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    Ca3-xSrxCo4-yCuyO9+δ (x=0, 0.1, 0.3; y=0, 0.05, 0.1) samples were prepared by using a conventional ceramic method. The crystal structure, bulk density and thermoelectric properties of the samples were investigated. In the X-ray diffraction patterns of the samples sintered at 1100°C, the single phase of Ca3Co4O9+δ was obtained. Lattice constants were increased with x and y, which suggested that Sr and Cu were substituted for Ca and Co in the Ca3Co4O9+δ structure, respectively. The sample with x=0.3 and y=0.1 got the highest density because the grain size bacame small and the void was removed.
    The highest density sample had the highest conductivity in all samples. The Seebeck coefficient didn't change by substitution. As a result, the sample with x=0.3 and y=0.1 had the highest power factor in all samples because of increase of the conductivity by substitution.
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  • Thermoelectric Properties of Higher Manganese Silicide Compounds Synthesized by MG-PDS Method
    Masaaki Yoshikura, Takashi Itoh
    2010 Volume 57 Issue 4 Pages 242-246
    Published: 2010
    Released on J-STAGE: July 06, 2010
    DOIhttps://doi.org/10.2497/jjspm.57.242
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    Higher manganese silicide (HMS) is a candidate for the low-cost and environment-friendly thermoelectric materials available to the thermoelectric power generation recovering waste heat. In this study, we synthesized HMS compounds by a combined method of mechanical grinding and pulse discharge sintering (MG-PDS), and measured their thermoelectric properties. Each of pure Mn and Si powders was mechanically ground using a planetary ball milling equipment at 400 rpm for 3 h. The ground powders with particle size of 44 μm or less were individually collected by sieving. After mixing by using a rotary blender at 60 rpm for 1 h, HMS compound was synthesized from the powder mixture and simultaneously consolidated by PDS at 1173 K for 15 min under 60 MPa in a vacuum atmosphere. Si ratio in MnSix was changed from x=1.73 to 1.9. Effect of the Si ratio on microstructure and thermoelectric properties was investigated. The maximum dimensionless figure of merit ZT=0.83 was achieved at 818 K in MnSi1.84 sample.
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  • Metal Doping Effects on the Conduction Type and the Thermoelectric Properties of β-FeSi2
    Tao Jiang, Takashi Sakai, Tomonori Fukuoka, Masaaki Miyamoto
    2010 Volume 57 Issue 4 Pages 247-251
    Published: 2010
    Released on J-STAGE: July 06, 2010
    DOIhttps://doi.org/10.2497/jjspm.57.247
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    Fe, Si and metal (Mn, Cu, Al) powders were mixed by ball-milling for 1 hour in an argon atmosphere. Mixtures of Fe, Si and metal (Mn, Cu, Al) powders were hot-pressed at 1373 K for 1 hour under 46.8 MPa and heat treated at 1123 K for 12 hours in an argon atmosphere. The conduction type of FeSix depends strongly on the composition ratio (x) of Si/Fe. The Seebeck coefficient at the composition range of 1.80≤x≤2.08 is positive, but negative in the range of 2.10≤x≤2.30 in the temperature range 300-780 K. One metal doping (Cu or Al) to the FeSi2.06, enhanced the positive value of Seebeck coefficient (α) and that to the FeSi2.15, enhanced the negative value of α. On the other hand, both Mn doped FeSi2.06 and FeSi2.15 showed the positive value of α. Doping effects of two metal elements (Mn-Cu, Mn-Al) to the FeSi2.06 were investigated. Doping of Mn-Al to the FeSi2.06 enhanced the Seebeck coefficient (α) and lowered the resistivity at high temperature range. The Seebeck coefficient of Mn-Al doped β-FeSi2 (Fe0.97Mn0.03Si2.06Al0.05) showed the maximum value 279.15 [μV/K] at 773 [K].
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  • Synthesis of Thermoelectric Bi-Sb Alloy Nanoparticles through Modified Polyol Process
    Yuusuke Tanaka, Takashi Itoh
    2010 Volume 57 Issue 4 Pages 252-256
    Published: 2010
    Released on J-STAGE: July 06, 2010
    DOIhttps://doi.org/10.2497/jjspm.57.252
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    Bi-Sb alloy is a promising thermoelectric material that has a good thermoelectric performance at temperature below the freezing point. This material is useful for Peltier refrigeration and/or thermoelectric power generation recovering cold potential from LNG. We attempted to synthesize nanoparticles of the Bi-Sb alloy through a modified polyol process. Two kinds of precursors, Bi(NO3)3·5H2O and Sb(CH3COO)3 (total amount 3 mmol) were dissolved in tetraethyleneglycole (TEG, 60 ml). A reducing agent NaBH4 (12 mmol) dissolved in TEG (10 ml) was added into the solution, then the Bi-Sb alloy was synthesized by heating to 373∼453 K. The synthesized particles in the solution were settled by centrifugation, washed with deionized water and ethanol, and dried under a vacuum. The reaction products were characterized by X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectrometry (ICP-AES) and transmission electron microscopy (TEM). Bi-Sb alloy phase was identified. Formation of the Bi-Sb alloy particles with nano size was confirmed. The particle size was increased with rising reaction temperature and alloy composition was controlled with molar proportion of the precursors.
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