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Theoretical Study. of MnSi compounds. about. thermoelectric. materials. Yoshida laboratory Hiromi Okubo. CONTENTS. 1. Introduction. 2. Theory. 3. Calculation method. 4. Results & discussion. 5. Summary. 6. Future. 1 . introduction. - About Thermoelectric Effects.
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Theoretical Study of MnSi compounds about thermoelectric materials Yoshida laboratory Hiromi Okubo
CONTENTS 1. Introduction 2. Theory 3. Calculation method 4. Results & discussion 5. Summary 6. Future
1. introduction - About Thermoelectric Effects Thermoelectric Effect A voltage drop A temperature gradient The Seebeck Effect The Peltier Effect V＝S・ΔT Q＝Π・ I (Kelvin's Relation) Π＝ TS The Peltiercoefficient The Seebeckcoefficient
1. introduction - About Thermoelectric device Thermoelectric device
1. introduction Industrial materials In 1960~70s Bi2Te3 Refrigerator Wine cellar Carnot efficiency7% Became common Advantage Nobody has researched Energy and environmental issues ・Generation by waste heat ・Cooling without Freon gas But now! That is receiving a lot of attention again!! from the viewpoint of environmental problems. ・maintenance free ・longevity http://www.nsst.nssmc.com/tsushin/magazine/33_2.pdf http://www.nistep.go.jp/achiev/ftx/jpn/stfc/stt090j/0809_03_featurearticles/0809fa02/200809_fa02.html
1. introduction Materials being studied Metal oxide Telluridecompounds AgSbTe2/GeTe CaCoO3 • Bi2Te3/Sb2Te3 NaCo2O4 • Bi2Te3 • , • , • PbTe • , SrTiO3/SrTiO3:Nb Sillicide compounds Heavy element→poison Low efficiency • Mg2Si • SiGe • , • β-FeSi2 • , • MnSi1.73 • Ba8Si46 • , Antimony compounds • CeFe3CoSb12 • ZbSb • , • Zn4Sb3 • LaFe3CoSb12 • , complex fabrication process
1. introduction si化合物の 具体例 しかしこの中でも MnSiはMnもSi大量にあるので これで行こう！ Sillicide compounds ManganSilicide a relatively high performance • Mg2Si • SiGe • , • β-FeSi2 • , p type thermoelectric material • MnSi1.73 • Ba8Si46 • , Clarke number 12 Clarke number 2 abundant Problems crystal polymorph
1. introduction MnxSiy Manganese Silicides • crystal polymorph • Mn4Si7 MnSi • Mn5Si2 • Mn3Si • Mn5Si3 • Mn6Si7 • Mn4Si • Mn6Si • Mn11Si19 • Mn27Si47 • , Theoretical Analytics
2. Theory ZT Performance index Figure of Merit σ 2 ZT A dimensionless quantity S σ σ Electric conductivity S Seebeck coefficient S semiconductor Thermal conductivity Carrier concentration A carrier concentration of about 1019cm-3 A.F.Ioffe, "Semiconductor Thermoelements and Thermoelectric cooling" , Infosearch Ltd. London(1957)
2. Theory thermoelectric property Figure of Merit Conductivity tensor Boltzmann equation + Band Theory energy-dependent
τ 2. Theory the relaxation time • experiment result τ Temperature dependncy of logμ μ: Carrier mobility • experiment value 0(K),300(K) x τ ZT logT
3. Calculation method FLAPW method DFT(Density Functional Theory) LDA(Local Density Approximation) ABCAP Cutoff-energy = 24Hr = 326.4eV k-points 6×6×6
3. Calculation method muffin‐tin approximation APW method V(r) expanded function constant R inside MT SPHERICAL WAVE outside PLANE WAVES spherically-symmetric potential r
4. Results Mn3Si Space group Fm-3m (225) Lattice parameter a = 0.5722[nm]
4. Result of thermoelectric properties Electron doped “ S “ Hole doped “ S “ Electron doped “ power factor σS^2 “ Hole doped “ power factor σS^2 “
5. Summary I calculatedthe electronic structure and thermoelectric properties of Mn3Si in MnSi compounds Result of the calculation of this study is that Mn3Si is metal. It is shown quantitatively that Mn3Si has low The Seebeck coefficient and its thermoelectric properties is not so good.
6. Future I will calculate other structures and affirmthe effect of impurities, and elucidate the mechanisms of substance MnSi system of high efficiency. In the future I want to find the ideal thermoelectric material.
