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(a) X-ray diffractogram from a Bi2Te3 nanostructured bulk pellet fabricated by cold pressing and sintering assemblies of nanoplate crystals, such as the examples shown in the SEM in (b). Inset in (a) is a bright field TEM micrograph of a Bi2Te3 nanoplate crystal with a 200 nm scale bar. Bright field TEM micrographs from a pellet showing (c) nanopores, (d) nanograins, and (e) their size distributions. The insets depict high-magnification micrographs showing (c) anisotropic nanopores in the host nanograin and (d) nanograins. Scale bars connote 50 nm.
(a) Room-temperature (300 K) thermal and electrical conductivities of Bi2Te3 nanoporous pellets with different pore volume fractions, namely, ∼5% (triangles), ∼10% (diamonds), and ∼25% (circles). (b) Lattice thermal conductivity κL plotted as a function of temperature. The triangles, diamonds, and circles represent the experimentally determined data points. The dashed-curves are predictions of a modified Debye-Callaway model combined with the modified effective medium theory.
Room temperature predictions of (a) phonon mean free path lmfp and (b) cumulative lattice thermal conductivity κL as a function of phonon wavelength λph for four pellets with 25% porosity, with different pore (P) and grain (G) sizes. Macrograins and macropores are defined as grains and pores with sizes much larger than lmfp.
(a) Electron mobility μ and (b) Seebeck coefficient α and power factor α2σ plotted as a function of electron concentration n for nanoporous Bi2Te3. The points are experimental data, the bold line is to guide the eye, and the dashed lines in (a) connote literature data trends for single crystal Bi2Te3 along and  crystallographic directions (Ref. 21).
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