Introduction Table 1. Summary of excess energies to be supplied for interstitial occupancy into one...
1
Introduction Table 1. Summary of excess energies to be supplied for interstitial occupancy into one of 4b sites or substitutional occupancy of a Mg site or a Si site of Mg 8 Si 4 by X (X = Cu, Ag, or Au) to proceed Intersti tial Mg 8 Si 4 X 1 Mg substitutio n Mg X Si Si substituti on Mg Si X Cu +0.863 p-type +1.107 +1.059 Au +0.034 +0.349 -0.515 n-type Ag +0.722 p-type (4 sites) +0.733 p-type (8 sites) +0.721 n-type (4 sites) Ag@ 2GPa +0635 +0.773 +0.815 Method: CASTEP LDA-GGA Mg Si Bi Te Pb Co Sb Reserves /ppm 32,0 00 267,7 00 0.06 5(ppb) 8 29 0.2 Price 100 45 245 4500 49 175000 0 215 Harmless O O X X X X X Calculation XRD @ High Temp. The reuse of waste heat energy is expected as one of the solutions of the environmental issues. It is necessary for the recovery of the waste heat energy to investigate the high- performance thermoelectric device which consists of N-type and P-type semiconductors. Moreover it is important for the industry and the environment to research the ecological friendly semiconductor which has abundant deposit on the earth and is harmless for the health. The synthesis is difficult, because the boiling point of Mg （ 1363K ） is close to the melting point of Mg 2 Si （ 1358K ） . Mg Mg Mg Mg Thermoelec tric properties S:Seebeck coefficient ρ:Electrical conductivity κ:Thermal conductivity Fig.1 Performance of several thermoelectric materials Fig.2 The synthetic condition of Mg 2 Si. Fig.3 Crystal structure of Mg 2 Si. (anti CaF 2 -type: ) Experiment Purpose • To find the synthetic condition for Ag-doped Mg 2 Si by high-temperature and high-pressure XRD (Multi Press) • To calculate the suitable dopant element for P- type • To synthesize the thermoelectric material (Piston Cylinder) and evaluate the thermal property Fig. 12 Electronic densities of states of (1)undoped Mg 54 Si 27 (2)Mg 64 Si 32 Cu 1 (3)Mg 53 Si 27 Ag 1 (4)Mg 54 Si 26 Au 1. Arrows in the Figures show intrinsic energy band gaps. Fermi energies are aligned with 0eV. Fig. 8 Photograph of an electric furnace and automatic control system. Fig. 15 EDX diffraction patterns of Ag-doped Mg 2 Si at 673 K, 1 GPa for various synthesis-time. Diffraction peaks of Mg decreased with increasing synthesis-time, their peaks almost disappeared after 8hrs. Fig. 4 Photographs of the starting materials for the XRD study of Ag-doped Mg 2 Si under high-temperature and high-pressure. The left two material are Mg(1) with particles 150 mm in diameter, and Si(2) powder and the right one is pure Mg 2 Si(3) synthesized by Union Material Co., Ltd. The average diameters of the particles of Si were (A)~150mm, (B) ~40mm, (C)~20mm, (D) ~3mm. Fig. 13 EDX diffraction patterns of Mg 2 Si under high-temperature at 1 GPa. The starting material of left figure (1) is Mg and Si powders. Mg 2 Si was synthesized at 573 K which temperature is very low than the melting point of Mg (923 K). Mg peaks disappeared and a broad peak appeared at 973 K. The quenched sample (top of the (1)) does not include Mg and Si. In the right figure (2), the starting material is powdered pure Mg 2 Si synthesized by Union Material Co., Ltd. Some peaks of MgO appeared with increasing temperature. • XRD under pressure by synchrotron radiation source at Photon Factory in Tsukuba BeamLine: PF-AR-NE5C Pressure technique: Multi Press (MAX80) Fig. 14 EDX diffraction patterns of Ag-doped Mg 2 Si under high- temperature at 1 GPa. The starting materials of the left (1) and the right (2) are Mg, Si, Ag and Mg 2 Si, Ag , respectively. In the left figure, Mg 2 Si was synthesized at 523 K and Mg peaks disappeared and broad peak appeared at 873 K. There temperatures are lower than the case of undoped sample. Ag peaks disappeared 823 K. However, in the right figure, Ag peaks remains still 873 K. The result means that in the case of Ag- doping , the Mg and Si powders are better than Mg 2 Si powder as the starting material. (2 ) (1 ) Summary • The first principle calculation expects that Ag is suitable doping element for the P-type conduction of Mg 2 Si and the pressure is effective for the Ag-doping. • In the case of mixture of Ag, Mg, Si powders, Mg 2 Si was synthesized at 523 K, and Ag peaks disappeared at 823 K and MgO or SiO 2 peaks did not appeared. This work was supported by MEXT KAKENHI(C) Grant Number 11013342, and has (2 ) (1 ) (1 ) (2 ) (3 ) a = 0.6340 nm S.G. = Fm-3m X-ray diffraction studies of Mg 2 Si and Ag-doped Mg 2 Si under pressure Y.Mori , Y.Kaihara, K.Takarabe : Okayama University of Science M1.00064 3.1mm Si:(D) Fig.6 Particle size distribution of Si powder (D). Fig.5 SEM image of mixture of Mg and Si powders. Fine Powder of Sample XRD under HP Thermal properties Fig.7 High-pressure equipment and sample assembly. Fig. 9 Photograph of the sampling plate for the thermoelectric properties. The properties of the small sample such as 5mm in diameter were measured by using this plate. Fig.10 Electrical conductivity of the standard sample of Mg 2 Si was measured. Fig.11 Seebeck coefficients of the standard sample and the synthesized Mg 2 Si under pressure(red). 40 60 80 100 Ag(311) Ag(220) Ag(200) Ag(111) 511,333 422 331 400 420 220 311 220 200 111 Si(400) Si(331) M g(112) Si(311) M g(012) Si(220) Si(111) M g(021) M g(112) M g(013) M g(110) M g(011) M g(002) Energy 2=6.0 deg. /keV 300K 873K 823K 723K 673K 523K 300K M g(010) P=1.0 G Pa M g+Si+Ag 40 60 80 100 Si(220) Si(311) Si(400) Si(111) M gO(111) M gO(220) 511,333 422 331 400 420 220 311 220 200 111 Energy 2=6.0 deg. /keV 300K 873K 823K 723K 673K 523K 300K P=1.0 G Pa Mg 2 Si+Ag Ag(111) Ag(200) Ag(220) Ag(311) T S ZT 2 40 60 80 100 511,333 422 331 400 420 220 311 220 200 111 Si(400) Si(331) Mg(112) Si(311) M g(012) Si(220) Si(111) M g(021) Mg(112) Mg(013) Mg(110) M g(011) Mg(002) 300K 973K 873K 773K 673K 573K 300K Mg(010) P=1.0 G Pa M g+Si 40 60 80 100 511,333 422 331 400 420 220 311 220 200 111 300K 973K 873K 773K 673K 573K 300K P=1.0 G Pa Mg 2 Si 30 40 50 60 70 80 In te n sity(a rb .u n it) 673 K E nergy 2 =6.0 deg /K eV M g 2 S i M gO RT Ag M g 2 S i M g 2 S i Ag Mg RT 1h 3h 6h 8h 400 500 600 700 800 900 200 400 600 800 1000 E lectrica lco n d u ctivity / S m -1 Tem perature /K 400 500 600 700 800 900 -500 -450 -400 -350 -300 -250 -200 -150 -100 -50 0 S e e b e ck co e fficie n t / m VK -1 Tem perature /K
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Transcript of Introduction Table 1. Summary of excess energies to be supplied for interstitial occupancy into one...
Introduction
Table 1. Summary of excess energies to be supplied for interstitial occupancy into one of 4b sites or substitutional occupancy of a Mg site or a Si site of Mg8Si4 by X (X = Cu, Ag, or Au) to proceed
Interstitial Mg8Si4X1
Mg substitution Mg7X1Si16
Si substitution Mg8Si3X1
Cu+0.863p-type +1.107 +1.059
Au +0.034 +0.349-0.515n-type
Ag+0.722p-type (4 sites)
+0.733p-type
(8 sites)
+0.721n-type
(4 sites)
Ag@ 2GPa +0635 +0.773 +0.815
Method: CASTEP LDA-GGA
Mg Si Bi Te Pb Co Sb
Reserves /ppm
32,000 267,700 0.06 5(ppb) 8 29 0.2
Price 100 45 245 4500 49 1750000 215
Harmless O O X X X X X
40 60 80 100
Ag(
311)
Ag(
220)
Ag(
200)
Ag(
111)
511,
333
422
331
400
420
220
311
220
200
111
Si(4
00)
Si(3
31)
Mg(
112)
Si(3
11)
Mg(
012)
Si(2
20)
Si(1
11)
Mg(
021)
Mg(
112)
Mg(
013)
Mg(
110)
Mg(
011)
Mg(
002)
Energy2=6.0 deg.
/ keV
300K 873K 823K 723K 673K 523K 300K
Mg(
010)
P=1.0 GPaMg+Si+Ag
40 60 80 100
Si(2
20)
Si(3
11)
Si(4
00)
Si(1
11)
MgO
(111
)
MgO
(220
)
511,
333
422
331
400
420
220
311
220
200
111
Energy2=6.0 deg.
/ keV
300K 873K 823K 723K 673K 523K 300K
P=1.0 GPaMg
2Si+Ag
Ag(
111)
Ag(
200)
Ag(
220)
Ag(
311)
Calculation
XRD @ High Temp.
The reuse of waste heat energy is expected as one of the solutions of the environmental issues. It is necessary for the recovery of the waste heat energy to investigate the high-performance thermoelectric device which consists of N-type and P-type semiconductors. Moreover it is important for the industry and the environment to research the ecological friendly semiconductor which has abundant deposit on the earth and is harmless for the health.
The synthesis is difficult, because the boiling point of Mg （ 1363K ） is close to the melting point of Mg2Si（ 1358K ） .
Mg
Mg
Mg
Mg
Thermoelectric properties
TSZT
2
S:Seebeck coefficientρ:Electrical conductivityκ:Thermal conductivity
Fig.1 Performance of several thermoelectric materials Fig.2 The synthetic condition of Mg2Si.Fig.3 Crystal structure of
Mg2Si. (anti CaF2-type: )
Experiment
Purpose
• To find the synthetic condition for Ag-doped Mg2Si by high-temperature and high-pressure XRD (Multi Press)
• To calculate the suitable dopant element for P-type• To synthesize the thermoelectric material (Piston Cylinder) and
evaluate the thermal property
Fig. 12 Electronic densities of states of (1)undoped Mg54Si27 (2)Mg64Si32Cu1 (3)Mg53Si27Ag1 (4)Mg54Si26Au1. Arrows in the Figures show intrinsic energy band gaps. Fermi energies are aligned with 0eV.
Fig. 8 Photograph of an electric furnace and automatic control system.
Fig. 15 EDX diffraction patterns of Ag-doped Mg2Si at 673 K, 1 GPa for various synthesis-time. Diffraction peaks of Mg decreased with increasing synthesis-time, their peaks almost disappeared after 8hrs.
Fig. 4 Photographs of the starting materials for the XRD study of Ag-doped Mg 2Si under high-temperature and high-pressure. The left two material are Mg(1) with particles 150 mm in diameter, and Si(2) powder and the right one is pure Mg2Si(3) synthesized by Union Material Co., Ltd.The average diameters of the particles of Si were (A)~150mm, (B) ~40mm, (C)~20mm, (D) ~3mm.
Fig. 13 EDX diffraction patterns of Mg2Si under high-temperature at 1 GPa. The starting material of left figure (1) is Mg and Si powders. Mg2Si was synthesized at 573 K which temperature is very low than the melting point of Mg (923 K). Mg peaks disappeared and a broad peak appeared at 973 K. The quenched sample (top of the (1)) does not include Mg and Si. In the right figure (2), the starting material is powdered pure Mg2Si synthesized by Union Material Co., Ltd. Some peaks of MgO appeared with increasing temperature.
• XRD under pressure by synchrotron radiation source at Photon Factory in Tsukuba
BeamLine: PF-AR-NE5C Pressure technique: Multi Press (MAX80)
Fig. 14 EDX diffraction patterns of Ag-doped Mg2Si under high-temperature at 1 GPa. The starting materials of the left (1) and the right (2) are Mg, Si, Ag and Mg2Si, Ag , respectively. In the left figure, Mg2Si was synthesized at 523 K and Mg peaks disappeared and broad peak appeared at 873 K. There temperatures are lower than the case of undoped sample. Ag peaks disappeared 823 K. However, in the right figure, Ag peaks remains still 873 K. The result means that in the case of Ag-doping , the Mg and Si powders are better than Mg2Si powder as the starting material.
(2)(1)
Summary• The first principle calculation expects that Ag is suitable doping element for the
P-type conduction of Mg2Si and the pressure is effective for the Ag-doping.
• In the case of mixture of Ag, Mg, Si powders, Mg2Si was synthesized at 523 K, and Ag peaks disappeared at 823 K and MgO or SiO2 peaks did not appeared.
This work was supported by MEXT KAKENHI(C) Grant Number 11013342, and has been performed under the approval of the Photon Factory Program Advisory Committee (Proposal No. 2010G668, 2012G566).
40 60 80 100
511,
333
422
33140
0
420
220
311
220
200
111
Si(4
00)
Si(3
31)
Mg(
112)
Si(3
11)
Mg(
012)
Si(2
20)
Si(1
11)
Mg(
021)
Mg(
112)
Mg(
013)
Mg(
110)
Mg(
011)
Mg(
002)
300K 973K 873K 773K 673K 573K 300K
Mg(
010)
P=1.0 GPaMg+Si
40 60 80 100
511,
333
422
331
400
420
220
311
220
200
111
300K 973K 873K 773K 673K 573K 300K
P=1.0 GPaMg
2Si(2)(1)
(1) (2) (3)
a = 0.6340 nmS.G. = Fm-3m
X-ray diffraction studies of Mg2Si and Ag-doped Mg2Si under pressure
Y.Mori , Y.Kaihara, K.Takarabe : Okayama University of Science
M1.00064
3.1mm
Si:(D)Fig.6 Particle size distribution of Si powder (D).
Fig.5 SEM image of mixture of Mg and Si powders.
30 40 50 60 70 80
Inte
nsi
ty(a
rb.u
nit)
673 K
Energy2=6.0 deg
/ KeV
Mg 2S
i
MgO RT
Ag
Mg 2S
i
Mg 2S
i
Ag
Mg
RT
1h
3h
6h
8h
400 500 600 700 800 900
200
400
600
800
1000
Ele
ctrica
l conduct
ivity
/ S
m-1
Temperature / K
400 500 600 700 800 900-500
-450
-400
-350
-300
-250
-200
-150
-100
-50
0
See
beck
coe
ffic
ient
/
VK
-1
Temperature / K
Fine Powder of Sample
XRD under HP
Thermal properties
Fig.7 High-pressure equipment and sample assembly.
Fig. 9 Photograph of the sampling plate for the thermoelectric properties. The properties of the small sample such as 5mm in diameter were measured by using this plate.
Fig.10 Electrical conductivity of the standard sample of Mg2Si was measured.
Fig.11 Seebeck coefficients of the standard sampleand the synthesized Mg2Si under pressure(red).
