Fabrication Of Bi2te3 And PbTe Based Thermoelectric Materials Using Hot Pressed Method And Its Seebeck Coefficient Under Large Temperature Difference
Thermoelectric material is useful in converting heat waste to electricity as long there isexist of temperature difference (ΔT). Bismuth telluride (Bi2Te3) and lead telluride (PbTe) based thermoelectric (TE) materials are state-of-art materials at a low and medium temperature range of 300 – 500 K...
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| Summary: | Thermoelectric material is useful in converting heat waste to electricity as long there
isexist of temperature difference (ΔT). Bismuth telluride (Bi2Te3) and lead telluride
(PbTe) based thermoelectric (TE) materials are state-of-art materials at a low and
medium temperature range of 300 – 500 K and 500 – 900 K, respectively. Seebeck
coefficient is one of the thermoelectric properties that determine its performance
through dimensionless figure-of-merit (ZT). The common fabrication method of TE
materialsis using the spark plasma sintering (SPS) under high pressure (20 to 50 MPa),
temperature (773 to 1373 K) and under the flow of current due to its high performances
output and a short time (5 to 30 minutes). However, the equipment is not available in
Malaysia. On the other hand, the measurement of Seebeck conventionally made using
a hot probe is measured under a small temperature difference (sΔT) which doesn’t
represent the real condition of operation of the material. Therefore, this study is to
investigate an alternative fabrication method using a widely available hot press
machineand study its Seebeck behaviour under large temperature differences (lΔT).
Four targettypes of samples were made using this method, which is n-Bi2Te2.7Se0.3, n PbTe0.8Se0.2,p-Bi0.3Sb1.7Te3 and p-Pb0.4Sn0.6Te. Two methods of preparation ofsample
were studied,using atomic mass and volume ratio method. In the atomic mass method,
the total molecular weight of the compound was calculated followed by the percentage
mass ofeach material to get the total density of the compound. Then, the total mass of
compoundpowder was calculated to produce the mass of each material. Meanwhile, in
the volumeratio method, the density of each material in the compound was used to
calculate the required amount of each compound. Samples were then compressed
under varied pressure, temperature and time to obtain optimization. Compositions of
samples were confirmed using the Energy Dispersive Spectroscopy (EDS) while
Seebeck and resistivity samples were measured using an in-house hot probe and 4-
point probe. This study successfully fabricated Bi2Te3 and PbTe based bulk
thermoelectric materials using the hot press method. Samples using atomic mass (AM)
calculation show the closest composition ratio of n- Bi2.2Te2.6Se0.2, p- Bi0.6Sb1.6Te2.8,
n-Pb1.1Te0.7Se0.2 and p-Pb0.7Sn0.2Te1.1 which fabricated under pressure and holding
time of 13 MPa and 17 minutes at a temperature of 423 K and 493 K respectively.
Seebeck for n-Bi2.2Te2.6Se0.2at room temperature is -53 µV/K which gives 65% lower
compared to the literature composition of Bi2Te2.7Se0.3 but n-Pb1.1Te0.7Se0.2 samples
give similar Seebeck of -249 µV/K. Similar results were obtained for both p Bi0.6Sb1.6Te2.8 and p-Pb0.5Sn0.2Te1.1 samples which shows a significant difference in
lΔT as compared to sΔT of literature. On the other hand, all samples showed slightly
higher electrical resistivity than in the literature also has been discussed. It can be
concluded that thermoelectric materials could be fabricated using the hot press method
as an alternative method at a lower cost.Although its performance is lower than the
SPS method, it could be improved by increasing the temperature, pressure and time.
The implication of this study could encourage high-performance thermoelectric
materials study in Malaysia and develop aninterest in waste heat recovery. |
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