Enhanced Thermoelectric Properties of FeSb x Nanocomposites Through Stoichiometric Adjustment
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Enhanced Thermoelectric Properties of FeSbx Nanocomposites Through Stoichiometric Adjustment Mani Pokharel1, Huaizhou Zhao1, Kevin Lukas1, Zhifeng Ren1, and Cyril Opeil1 1
Department of Physics, Boston College, Chestnut Hill, Massachusetts 02467, USA
ABSTRACT The Seebeck coefficient, electrical resistivity, thermal conductivity and Hall coefficient of FeSbx (x = 2.04, 2.00, and 1.96) nanocomposites hot pressed at 300 °C were measured. The power factor of FeSb1.96 was increased by 105% compared to FeSb2. Hall coefficient measurements revealed a decreased carrier concentration and increased mobility in FeSb1.96 with an overall enhancement in ZT of 45% in FeSb1.96 .
INTRODUCTION FeSb2, a strongly correlated semiconductor, has recently stimulated extensive research efforts due to its promising thermoelectric properties at cryogenic temperature [1-7]. Although it had been one of the well- studied compounds in the past few decades [8-12], the renewed interest in this compound came after Beniten et al.[1] reported a colossal Seebeck coefficient of - 45,000 μVK-1 on single crystal samples with a huge power factor (PF) of 2.3× 10-1 WK-2m-1 at ~ 10 K. Unfortunately, even with such a large PF, the value of ZT, defined by
,
(1)
for single crystals is very low due to the large value of the thermal conductivity which reaches ~ 500 Wm-1K-1 at around 10 K. Here S is the Seebeck coefficient, ρ the electrical resistivity, 𝜅 the thermal conductivity and T the absolute temperature. In general,
𝜅
𝜅
𝜅
(2)
where 𝜅 and 𝜅 are electronic and lattice contributions to thermal conductivity, respectively. In our earlier report [13], we presented a dramatic reduction of lattice thermal conductivity leading to a large increase in ZT by a factor of about 2. However in those samples, the PF was drastically reduced when compared to the single crystal values. Given that the Seebeck coefficient of FeSb2 is very sensitive to carrier concentration [8,9] , in this work we aim to increase the power factor through stoichiometric adjustment which should have negligible effect on the thermal conductivity.
EXPERIMENTAL DETAILS The nanostructured FeSbx samples were synthesized by first forming an ingot through melting and solidification. The ingot was then ball milled and hot pressed at 300°C to obtain the three nanocomposite (NC) samples namely: FeSb2, FeSb2.04, and FeSb1.96. The Seebeck Coefficient (S), electrical resistivity (ρ), thermal conductivity (κ) and Hall coefficient (RH) were all measured on a Physical Property Measurement System (PPMS) from Quantum Design. Sample preparation and measurements were done in the same manner as described in ref.[13].
DISCUSSION
FeSb2
FeSb2.04 -100
FeSb1.96
-120
-100 -140 30
(a)
40 T (K)
50
-4
10
-8
-10
0.00 -5
10
0
50
100
FeSb2.04 FeSb1.96
ln
Electrical Resistivity ( -m)
FeSb2
0
-1 S (V K )
Seebeck Coefficient (VK-1)
Figure 1 (a) shows the Seebeck coefficient of all the samples as a function of temperature.
150 T(K)
200
250
300
0.05
0.10
T-1 (K-1)
0.15
10
(b) 100
T(K
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