1 J. Hejtmánek and K. Knížek Institute of Physics of ASCR, v.v.i. , Na Slovance 2, 182 21 PRAHA 8, CZ Location: Cukrovarnicka 10, Prague 6, 162 53 [email protected], phone +420 2 303 18 419, fax +420 2 333 43 184 WWW: www.fzu.cz Measuring thermal and thermoelectric properties- principles, measuring techniques and analysis
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J. Hej tmánek and K. KnížekInstitute of Physics of ASCR, v.v.i. , Na Slovance 2, 182 21 PRAHA 8, CZ
Measuring thermal and thermoelectric properties- principles, measuring techniques
and analysis
2
Thermoelectric materials
Thermoelectricity-Thermoelectric conversion of energy – characteristics - Electrical resistivity-Thermoelectric power-Thermal conductivity, thermal diffusivity (Wiedemann-Franz law in “non metals”)
Measuring techniques – compendium of measuring techniques and analysis
--Low temperature systemsLow temperature systems – commercial (Quantum Design), Thermal transport option & home made inset (5-350 K), magnetic field -Home made sample holders objective to measure all thermoelectric characteristics simultaneously on one specimen (each specimen unique character) -close cycle refrigerators: Leybold ( 300>T>12 K) Janis (300> T>3.5 K) – snags,
-Home made High temperature cellsHigh temperature cells, principle, difficulties,calibration, reliability
3
(λ,α,ρ,κ)
λ,α,ρ,κ &
F= Distance/Area
E=V/Distance; J=I/Area
#
λλλλraw = Rheater I2/∆T*F
λλλλ = λλλλraw -λλλλrad -λλλλwires
#
ρ= Ε/J#
αααα = ∆V /∆T+ αleads
Distance-∆T and ∆V
T
∆Tup
∆T down
J
E
∆T Heater
Column
Name
A B C D E F G H I J
Signification
Temperature
∆T between ∆Tup and ∆Tdown
∆T between sample
center and sink
HeaterPower
Raw thermal
Conductivity
Corrected
Thermal Conducti
vity
Corrected
Seebeckcoefficien
t
Resistivity
Diffusivity
Heat capacity
Symbol
T ∆T ∆T P λraw λ TEP, S or α
ρ κ CV
Unity
K K K W Wm-1K-
1Wm-1K-
1µVK-1 mΩ.c
mmm2/s
J/K/ cm3
4
(λ,α,ρ,κ) λ,α,ρ,κ
4-point λ, λ, λ, λ, S and ρρρρ method for “ normal” samples
Mini heater
Anchoring Cu hoop (0.2 mm Wire) Up
Current lead Cr-Ni wire Down
E-thermocouple ∆T Up
Chromel wire as voltage lead
Anchoring Cu hoop (0.2 mm Wire) Down
Current lead Cr-Ni wire Up
E-thermocouple ∆T Down
Chromel wire as voltage lead
Connector Si calibrated diod Thermal anchor of
E-differential thermocouples
Sample
Pasted with Ag-filled
Cyanacrylate
Pasted with Ge varnish-separated
cigarette paper
Protective frame
E-thermocouple ∆T Heater
5
Thermal and electrical measurements I (λ,α,ρ)
Sample mounting, topology
Con-nector 1
∆∆∆∆Tup E-typ
2 ∆∆∆∆Tdown E-typ
3 ∆∆∆∆Vsample
Chromel
4 Tabs
(I , sense) Diode
5 Tabs
(U, input) Diode
6 Free
7 Heater
8200
8 I sample
H
gh
Used for
Ch 100, 709SCAN 712DMM
Ch 101, 709SCAN 712DMM
Ch 2, 722
MULT
Ch 323, 709SCANImikrosour
Ch 103, 709SCAN 712DMM
Ch 3, 722
MULT
Ch 200, 709SCAN 719Keithl
Ch 202, 709SCAN 719Keithl
Con-nector 9
∆∆∆∆Tup E-typ
10 ∆∆∆∆Tdown E-typ
11 ∆∆∆∆Vsample
Chromel
12 Tabs
(I , sense) Diode
13 Tabs
(U, input) Diode
14 Free
15 Heater
8200
16 Isample
Low Used
for Ch 100, 709SCAN 712DMM
Ch 101, 709SCAN 712DMM
Ch 2, 722
MULT
Ch 323, 709SCANImikrosour
Ch 103, 709SCAN 712DMM
Ch 3, 722
MULT
Ch 201, 709SCAN 719Keithl
Ch 203, 709SCAN 719Keithl
1 2 8
9 10 16
Steady state 4-point measurementAcquisition performed after temperature
(~50 mK) and thermal voltage (~1-5%+0.5µV) stability is achieved
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II (λ,α,ρ,κ,cv)
Low temperature 4-point cell Close cycle He-cryostat (3.5-300K)
Radiation shield
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(λ,α,ρ,κ,cv)
Ultra-low temperature 4-point cell
Close cycle He-cryostat (3.5-300K) operating
since 2006
Software--fully WXP 32 bit compatible, PCI HPIB card, external measuring system controlled via PC, program in DELPHI
Hardware--same cell , better temperature control needed, cold finger itself !! High temperature fluctuations!! + lower temperature,stronger requirements for temperature measurement and control!
Vacuum cover
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II (λ,α,ρ,κ,cv)
0 1 2 3 4 5 60
5
10
15
20
25
30
35
40
Tem
pera
ture
(K
)
Time (min)
1.5 2.0 2.5 3.0
5
10
15
20
9
II (λ,α,ρ,κ,cv) !
340 350 360 370 3803.0
3.2
3.4
3.6
3.8
4.0
4.2
4.4
4.6
4.8
5.0
T(set)= 3.2 K
Natural temperature fluctuationson cold finger
Abs
olut
e te
mpe
ratu
re (
K)
Time (sec)
14740 14750 14760 14770 14780
3
4
5
Temperature on measuring cell (after filtering)controlled by LakeShore
340 350 360 370 3803
4
5
6
7
8
Natural temperature fluctuationson cold fingerA
bsol
ute
tem
pera
ture
(K
)
Time (sec)
16160 16170 16180 16190 16200
3
4
5
6
7
8
Tup = Tabs+∆(T)up on the sample at 6 K after temperature stabilization
T(set)= 6 K
Temperature on measuring cell (after filtering)controlled by LakeShore
120 121 122 123 124 125 126 127 128 129 1308
10
12
14
Time (sec)
Natural temperature fluctuationson cold finger during cooling
0.8 PPMS Thermal transport Typical Accuracy: • ± 5 % or ± 2 µW/K, whichever isgreater, for T < 15 K• ± 5 % or ± 20 µW/K, whichever isgreater, for 15 K < T < 200 K• ± 5 % or ± 0.5 mW/K, whichever isgreater, for 200 K < T < 300 K• ± 5 % or ± 1 mW/K, whichever isgreater, for T > 300 K