The Influence of Sintering Temperature on the Microstructure and Thermoelectric Properties of n-Type Bi2Te3−x Se x Nanomaterials

Abstract

nanopowders were hydrothermally synthesized, and n-type Bi 2 Te 3Àx Se x bulk samples were prepared by hot pressing a mixture of Bi 2 Te 3 and Bi 2 Se 3 nanopowders at 623 K, 648 K or 673 K and 80 MPa in vacuum. The phase composition of the powders and bulk samples were characterized by x-ray diffraction. The morphology of the powders was examined by transmission electron microscopy. The microstructure and composition of the bulk samples were characterized by field-emission scanning electron microscopy and energy-dispersive x-ray spectroscopy, respectively. The density of the samples increased with sintering temperature. The samples were somewhat oxidized, and the amount of oxide (Bi 2 TeO 5 ) present increased with sintering temperature. The samples consisted of sheet-like grains with a thickness less than 100 nm. Seebeck coefficient, electrical conductivity, and thermal conductivity of the samples were measured from room temperature up to 573 K. Throughout the temperature range investigated, the sample sintered at 623 K had a higher power factor than the samples sintered at 648 K or 673 K.

Effects of Preparation Methods on the Thermoelectric Performance of SWCNT/Bi2Te3 Bulk Composites

“…The content of voids in CNT/BT-HP-648 is much lower than those of CNT/BT-PS-598, CNT/BT-PS-648, and CNT/BT-PS-698, mainly because CNT/BT-HP-648 has undergone a high pressure (80 MPa). An obviously oriented microstructure was observed in CNT/BT-HP-648 ( Figure 4d), mainly due to the anisotropy of Bi 2 Te 3 , which agrees with the results reported in Reference [24]. The peak intensity of the (0015) plane (~44.5 • ) significantly increases in CNT/BT-HP-648 ( Figure S1) when compared with the as-prepared composite powders (Figure 2), which also confirms the oriented microstructure of CNT/BT-HP-648.…”

“…No obvious characteristic peak of SWCNTs is observed as the content of SWCNTs increases from 0.25 to 0.75 wt %, mainly due to the low content of SWCNTs, which agrees with a previous report in Reference [17]. powders are matched with the standard JCPDF #15-0863 for Bi2Te3 [23,24]. No obvious characteristic peak of SWCNTs is observed as the content of SWCNTs increases from 0.25 to 0.75 wt %, mainly due to the low content of SWCNTs, which agrees with a previous report in Reference [17].…”

Thermoelectric Properties of Reduced Graphene Oxide/Bi2Te3 Nanocomposites

“…It can be seen that the particle size of the as-prepared Bi2Te3 is ~50-100 nm, and Bi2Te3 nanoparticles are uniformly decorated on rGO layers in the nanocomposites. which is mainly due to that the powders were slightly oxidized during the hot-pressing sintering [23]. The rGO/Bi 2 Te 3 composite powders were of nanosize and would adsorb oxygen on their surfaces, and the adsorbed oxygen could not be fully eliminated even the hot-pressing was carried out under vacuum [23].…”

“…70-5000), which is mainly due to that the powders were slightly oxidized during the hot-pressing sintering [23]. The rGO/Bi2Te3 composite powders were of nanosize and would adsorb oxygen on their surfaces, and the adsorbed oxygen could not be fully eliminated even the hot-pressing was carried out under vacuum [23]. The intensities of the (006) and (0015) planes for the rGO/Bi2Te3 nanocomposite bulk materials are significantly enhanced when compared to the powders (see Figure 2), which indicates the preferred orientation for the bulk materials after the hot-pressing sintering [29].…”

“…The α and C p were measured using LFA 467 (NETZSCH) from RT to 300 • C in Ar. The ρ was measured by the Archimedes method [23,24]. The relative density of the rGO/Bi 2 Te 3 nanocomposite bulk materials with different content of rGO was calculated by the ratio of the corresponding measured density: theoretical density.…”