Supplemental material:
Enhanced thermoelectric performance of nanostructured topological
insulator Bi2Se3
G.L. Sun,1,2 X.Y. Qin,1, a) D. Li,1 T.H. Zou,1 H.X. Xin,1 B.J. Ren,1 J. Zhang,1 Y.Y. Li1 and
X.J. Li1
1
Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, 230031 Hefei, P. R. China
2
School of Physics and Materials Science, Anhui University, Hefei 230039, P. R. China
Corresponding author. Tel:+86 0551 5592750; fax:+86 0551 5591434
E-mail address: xyqin@issp.ac.cn
(1) Experimental details
The Bi2Se3 alloy ingots were synthesized by melting method. High purity powders of Se (99.999%)
and granules of Bi (99.999%) were weighted according to according to the formula of Bi2Se3. The
powder mixture were sealed in cleaned quart tube for air exhausting by vacuum pump until the inner
pressure reach the high vacuum of 2.0×10-2Pa, and then placed in a digitally controlled furnace and
heated slowly (1K/min) to 1073K and isothermally kept 24h and finally naturally cooled to room
temperature. Then the ingots were ground into powders by the milling machine (Grind Man) (whose
mortar and pestle of the milling machine are made of agate) at the rotation speed of 80 r/min for
different milling time so as to obtain samples with different grain dimensions. The nanostructure bulk
cylinder-shaped samples with the size of 13mm in diameter and 2-10mm in thickness were prepared by
vacuum hot-pressing at 563K under a pressure of 600MPa for 60min. Bars of 228mm3 were cut from
the bulk disks and polished for measurements of thermoelectric transport properties. The phase
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compositions of bulk samples were characterized by XRD (PANanlytical X’Pert Pro X-ray diffraction)
using Cu-Kα radiation. The morphology was characterized by FESEM (SU8020). The measurement of
electrical resistivity and Seebeck coefficient were performed on commercial equipment (ZEM-3(M08),
Ulvac Riko, Inc.) by using a four-probe technique. The thermal diffusivity  was determined by a laser
flash method using the Netzsch LFA-457 system. The carrier density, carrier mobility was calculated
based on the Hall coefficient measurement which was carried out on a Physical Properties Measurement
System (PPMS) (Quantum Design) using the five-probe technique. The specific heat Cp was determined
by a commercial instrument (Pyris Diamond DSC, Perkine Elmer). The samples densities D measured
by the Archimedes’ method were about 93% of theoretical densities. The resulting thermal conductivity
 was calculated from the measured thermal diffusivity , specific heat Cp, and density D from the
relationship =DCp.
(2) Microstructural characterization
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FIG. S1. XRD patterns of the Bi2Se3 samples milled for different time. The pattern of JCPDS card
00-033-0214 is also given for comparison, where the stars indicates (006), (009), (0012), (0015), (0018)
and (0021) peaks, successively
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FIG. S2. SEM images of the fracture surfaces of as-prepared Bi2Se3 bulk samples. Therein, (a), (b), (c),
(d) and (e) correspond to the samples milled for tm=10, 20, 30, 40, and 50 min, respectively (please note
that the unit of the scale bar in (a) is different from that in the other images).
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FIG. S3. Transverse size (length) distributions of the Bi2Se3 samples with different milling time, which
are statistically determined from SEM images.
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Table SI A list of grain thickness dXRD (determined from XRD), dSEM (determined from FESEM) and
gain length LSEM (determined from FESEM) for the samples with different milling time tm.
NO.
tm(min)
S1#
S2#
S3#
S4#
S5#
10
20
30
40
50
dXRD(nm)
dSEM(nm)
LSEM(nm)
72
55
40
330
100
80
50
33
1010
370
112
98
73
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