Suppression of grain growth by additive in nanostructured p-type bismuth antimony tellurides

Abstract

Grain growth during hot pressing is a major issue in the preparation of nanostructured bismuth-antimony-tellurides during hot-pressing the nanopowders into dense bulk samples.To prevent grain agglomeration during ball milling and growth during hot pressing, organic agent (Oleic Acid, OA) as additive was added into the materials at the beginning of the ball milling process. With different concentrations of OA (0.5, 1.0, 1.5, 2.0, and 2.5 wt.%), grains with different sizes are obtained. Structural analysis clearly shows that it is the particle size of the nanopowders that determines the final grain size in the densely compacted bulk samples.A combination of small grains ~200-500 nm and nanopores leads to effective phonon scattering, which results in the decrease of lattice thermal conductivity, and ZT to ~1.3 at 373 K for the sample with a 2.0 wt.% OA as agent.

Lattice Thermal Conductivity Reduction Due to In Situ-Generated Nano-Phase in Bi0.4Sb1.6Te3 Alloys by Microwave-Activated Hot Pressing

“…Therefore, the decrease in q should result from the large increase in l and the slight decrease in n. The q value of the MAHP specimen in the present work is much higher than that of the HP-450 specimen reported in Ref. 27. Figure 8b shows the temperature dependence of a of the MAHP and the HP-450 specimens.…”

“…A peak PF value of 4.3 9 10 À3 W/(mAEK 2 ) is achieved at 52°C for the HP-450 specimen reported in Ref. 27.…”

“…27 The positive temperature dependence of q indicates a metallic conduction behavior for all MAHP specimens except for the MAHP-205 specimen. The q value of the MAHP-205 specimen decreases as the temperature increases.…”

“…Figure 8b shows the temperature dependence of a of the MAHP and the HP-450 specimens. 27 When the testing temperature is above 150°C, the a value decreases due to the intrinsic excitation and suppression of minority carrier in the heavily doped Bi 0.4 Sb 1.6 Te 3 alloys. 32 According to the Ioffe theory, a can be given by the equation: a µc-ln n, where c is the scattering factor.…”

“…27 The lattice thermal conductivity (j L ) can be determined by the WiedemannFranz relationship, j L = j-L 0 T/q, where L 0 T/q is electronic thermal conductivity (j e ) and L 0 is Lorenz constant, L 0 = 2.0 9 10 À8 V 2 /K 2 for a heavily doped semiconductor. 33 The j e value shows a downward trend with increasing testing temperature except for the MAHP-205 specimen because it is inversely proportional to q (Fig.…”