1. High temperature p - type and n - type thermoelectric properties of Pr1-xSrxFeO3 (0.1≦x≦0.9)
Hiroshi Nakatsugawa 1,＊, Itsuki Ishikawa 1, Miwa Saito 2, and Yoichi Okamoto 3
1Yokohama National University , 2Kanagawa University, and 3National Defense Academy
＊Corresponding author, TEL/FAX :
Polycrystalline samples of Pr1-xSrxFeO3 (0.1≦x≦0.9) were synthesized using a conventional solid-state reaction method. The perovskite structures changed from orthorhombic Pbnm phases to rhombohedral R-3c ones at x = 0.5. The temperature dependence of inverse magnetic susceptibilities (χ-χ0)-1 showed that the spin state of Fe ions consists of intermediate spin (IS) Fe3+ (t2g4eg1), low spin (LS) Fe3+ (t2g5), and LS Fe4+ (t2g4) ions below x = 0.7. On the other hand, the spin state of Fe ions consists of LS Fe3+ and LS Fe4+ ions in x = 0.8 and 0.9. This means that the carrier type for Pr1-xSrxFeO3 changes from t2g and eg holes like to t2g electron like behavior. In fact, the samples for x≦0.3 show a large positive Seebeck coefficient over the whole temperature range although positive Seebeck coefficient of the samples for 0.4≦x≦0.5 decreases with increasing temperature and that of the samples for 0.7≦x≦0.9 show a negative Seebeck coefficient over the whole temperature range. In particular, the sample with x = 0.1 showed a power factor of 20μWm-1K-2 at 850K leading to ZT of about at this temperature, indicating that perovskite-type Fe oxides are one of the good candidate for high temperature p - type thermoelectric oxides.
INTRODUCTION
INTRODUCTION
EXPERIMENTAL
EXPERIMENTAL
Fabrication
solid-state reaction method
stoichiometric mixture
calcined at 1000℃ in air
sintered at 1300℃ in O2
pressed into pellets
R-3c
T+ΔT
Heat Source h+ e-
Al doped ZnO
NaxCoO2
p - type
n - type
Heatsink T
Fig2. Seebeck coefficient in high temperature limit evaluated from an extended Heikes formula in LS Fe3+1-x LS Fe4+x
Determinaiton
イオン半径
(Å)
BVパラメーター
r0 (Å)
[Ca2CoO3]0.62CoO2
Ca0.9Yb0.1MnO3
powder X-ray , RINT2500
Rietveld analysis , RIETAN-FP program
χ ：5 - H = 1T , MPMS
ρ ： K, dc four-probe method
S ： K, steady-state technique
κ = dCvα
d：Archimedes SMK-401
Cv：differential scanning X-DSC7000
α： K, TC-7000
Fig1. Typical p-type and n-type thermoelectric oxides
Pbnm
Thermoelectric oxides module which consists of PN elements of small linear thermal expansion coefficient difference is desired.
PN elements should be fabricated by the same in composition.
We have studied specimens of Pr1-xSrxFeO3 (0.1≦x≦0.9).
Fig4. Powder X-ray diffraction patterns of Pr1-xSrxFeO3 (0.1≦x≦0.9) at room temperature
Fig3. Seebeck coefficient in high temperature limit evaluated from an extended Heikes formula in IS Fe3+1-x LS Fe4+x
RESULTS AND DISCUSSION
Crystal structure
Magnetic susceptibility
Electric resistivity
Thermal conductivity
Seebeck coefficient
120 minutes
120 minutes
Fig5. Fe - O distances in Pr1-xSrxFeO3 (0.1≦x≦0.9)
Fig7. χ-χ0 .vs. T for Pr1-xSrxFeO3 (0.1≦x≦0.9)
Fig9. ρ .vs. T for Pr1-xSrxFeO3 (0.1≦x≦0.9)
Fig11. S .vs. T for Pr1-xSrxFeO3 (0.1≦x≦0.9)
Fig14. κ and κe .vs. T for Pr1-xSrxFeO3 (0.1≦x≦0.9)
120 minutes
Fig10. σT .vs. T-1 for Pr1-xSrxFeO3 (0.1≦x≦0.9)
Fig12. S .vs. T-1 for Pr1-xSrxFeO3 (0.1≦x≦0.9)
Fig13. S2/L0 .vs. T for Pr1-xSrxFeO3 (0.1≦x≦0.9)
Fig15. κe / κ .vs. T for Pr1-xSrxFeO3 (0.1≦x≦0.9)
LS Fe4+
IS Fe3+
Power factor ZT
LS Fe3+
Fig8. (χ-χ0)-1 .vs. T for Pr1-xSrxFeO3 (0.1≦x≦0.9)
Fig6. Fe - O - Fe angles in Pr1-xSrxFeO3 (0.1≦x≦0.9)
Table I. Physical quantities obtained from magnetic susceptibility measurement for Pr1-xSrxFeO3 (0.1≦x≦0.9)
Fig16. S2σ .vs. T for Pr1-xSrxFeO3 (0.1≦x≦0.9)
Fig17 ZT .vs. T for Pr1-xSrxFeO3 (0.1≦x≦0.9)
Table II. Physical quantities obtained from thermoelectric properties measurement for Pr1-xSrxFeO3 (0.1≦x≦0.9)
SUMMARY
Pr1-xSrxFeO3 shows p - type thermoelectric properties for 0.1≦ｘ≦0.5 and n – type thermoelectric properties for 0.7≦x≦0.9.
Pr0.9Sr0.1FeO3 showed a p - type power factor of 20μWm-1K-2 at 850K leading to ZT of about at this temperature.
Pr0.3Sr0.7FeO3 showed an n - type power factor of 3μWm-1K-2 at 850K leading to ZT of about at this temperature.
It is expected that Pr0.3Sr0.7Fe1-xMnxO3 may be one of the good candidate for high temperature n - type thermoelectric oxides.
ACKNOWLEDGMENTS : This study has been partly supported by the Grants-in-Aid for Scientific Research #15K06479.