Research ArticleMATERIALS SCIENCE

Thermal conductivity in Bi0.5Sb1.5Te3+x and the role of dense dislocation arrays at grain boundaries

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Science Advances  01 Jun 2018:
Vol. 4, no. 6, eaar5606
DOI: 10.1126/sciadv.aar5606
  • Fig. 1 Phases composition before and after SPS sintering.

    (A to D) FESEM images of the free surface of melt-spun ribbons containing 0, 5, 15, and 25 wt % excess of Te, respectively. The red arrows in (B) to (D) show the dendritic boundaries in the ribbon, where single-phase Te distributed. (E) Displacement of a plunger as a function of temperature during SPS processing of melt-spun ribbons containing different excess amounts of Te. (F) XRD patterns of powders at different stages of processing. (G to I) Photos of graphite dies after SPS containing samples with 5, 15, and 25 wt % excess of Te. The material ejected during SPS is clearly seen. a.u., arbitrary units.

  • Fig. 2 The orientation of the sintered bulks.

    (A) XRD patterns of planes perpendicular to the pressure direction during SPS. (B) Relationship between the orientation factor F and the amount of excess Te. (C) FESEM images: Surface of a sample with no Te excess observed perpendicular to the pressing direction of SPS. (D) Surface of the same sample as in (C) but observed parallel to the pressing direction. (E) Surface of a sample containing 25 wt % excess of Te observed perpendicular to the pressing direction. (F) Surface of the same sample as in (E) but observed parallel to the pressing direction. The upper right corners show the relative directions marked in red.

  • Fig. 3 Microstructure of sintered bulks.

    (A) TEM image of a sample sintered from melt-spun ribbons containing 25 wt % excess of Te. The inset shows SAED of a narrow region (white circle) corresponding to the Bi0.5Sb1.5Te3 matrix. (B) A view of grain boundaries with the inset displaying images of FFT of the numbered regions. (C) Moiré pattern with the width of 40 nm in the boundary region. (D) An image of IFFT of (C) showing dislocations.

  • Fig. 4 Thermal properties of sintered bulks.

    Total thermal conductivity measured (A) perpendicular to and (B) parallel to the pressing direction for samples sintered from melt-spun ribbons of composition Bi0.5Sb1.5Te3+x wt % excess of Te (x = 0, 5, 10, 15, 20, and 25). κ|| and κ represent the total thermal conductivity measured parallel and perpendicular to the pressing direction, respectively. The red dashed line without symbol in (A) and (B) is the data of Kim et al. (16) for comparison. (C) Lattice thermal conductivity for the identical samples measured perpendicular to the pressing direction. The inset is the data of Kim et al. (16). (D) A relationship between the ratio of κ|| and the orientation factor F for sintered samples of composition Bi0.5Sb1.5Te3+x wt % excess of Te (x = 0, 5, 10, 15, 20, and 25). The line is the data of Shen et al. (18).

  • Fig. 5 Electrical properties of sintered bulks.

    (A) Electrical conductivity, (B) Seebeck coefficient, (C) the power factor, and (D) figure of merit ZT for samples sintered from melt-spun ribbons of composition Bi0.5Sb1.5Te3+x wt % excess of Te (x = 0, 5, 10, 15, 20, and 25) measured perpendicular to (solid lines with solid symbols, marked by “⊥”) and parallel to (dashed lines with open symbols, marked by “//”) the pressing direction. The suffix F means that the ZT is calculated using measurements of the electronic transport properties perpendicular to and the thermal conductivity κ parallel to the pressing direction, as done for samples with x = 20 and x = 25 designated by open triangles and open hexagons connected by solid curves. The red dashed line without symbol in (A) and (B) is the data of Kim et al. (16) for comparison.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/6/eaar5606/DC1

    fig. S1. Powder XRD patterns of melt-spun ribbons.

    fig. S2. FESEM images of two surfaces of ribbons.

    fig. S3. EDS of the free surface of ribbon containing 25 wt % extra Te.

    fig. S4. BSE images of SPS samples and ejected material.

    fig. S5. Carrier concentration and mobility of samples.

    table S1. Room-temperature physical parameters of samples.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Powder XRD patterns of melt-spun ribbons.
    • fig. S2. FESEM images of two surfaces of ribbons.
    • fig. S3. EDS of the free surface of ribbon containing 25 wt % extra Te.
    • fig. S4. BSE images of SPS samples and ejected material.
    • fig. S5. Carrier concentration and mobility of samples.
    • table S1. Room-temperature physical parameters of samples.

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