Electronic Supplementary information (ESI)
Influence of a Nanoscale Ag2Te Precipitates on the
Thermoelectric Properties of the Sn Doped P-Type
AgSbTe2 Compound
Rajeshkumar Mohanraman,1,
2, 3, a)
Raman Sankar,4 Fang-Cheng Chou,4 Chih-Hao
Lee,1 Yoshiyuki Iizuka,5 I Panneer Muthuselvam, 4 and Yang-Yuan Chen2, a)
1
Department of Engineering and System Science, National Tsing Hua University, Taiwan, ROC
2
Institute of Physics, Academia Sinica, Taiwan, ROC
3
Nano Science and Technology, Taiwan International Graduate Program, Institute of Physics,
Academia Sinica, Taiwan, ROC
4
Center for Condensed Matter Sciences, National Taiwan University, Taiwan, ROC
5
Institute of Earth Sciences, Academia Sinica, Taiwan, ROC
1
Site occupancy
FIG. S1 (a) and (b): Site occupancy as a function of the Sn composition for the
Ag(Sb1-xSnx)Te2 series.
Fig. 1(a) shows the site occupancy of the Ag, Sb, and Te atoms in their
respective sites as a function of the Sn content. A value of 1 means that the atoms
occupy their specific sites. Since the site occupancy of Te atoms keeps this constant
value of 1 (within the error bar of the analysis), the population of Te atoms is not
changed by the addition of Sn atoms and occupies the same sites as in the AgSbTe2
alloy case. The site occupancy of Ag atoms is slightly decreased with higher Sn
content means Ag vacancy has occurred due to formation of Ag2Te phase impurities.
Since Sb atoms are replaced by Sn atoms, compared to the stoichiometric composition,
the population of Sb atoms in Sb sites decreases.
Fig. 1(b) shows the site occupancy of the Sn atoms in the Sb sites. Indeed, it
is seen that the population of Sn atoms in Sb sites increases with the Sn content,
beyond that shows almost remains constant. Therefore, the existence of a second
phase is highly likely for highly-doped compositions.
2
Electron Probe Micro-Analysis (EPMA)
The chemical composition of the as-prepared ingots was determined using electron
probe micro analyses (FE-EPMA: JEOL JXA-8500F).
FIG. S2
EPMA sample preparation for Ag(Sb1-xSnx)Te2 samples.
Analytical procedure
Sections of run products were mounted into epoxy resin (Epofix: Struers Co) and
grinded with SiC (silicon carbide) papers until flat surface exposed, then polished
with diamond suspensions which particle size from 9µm, through 6µm and 3µm to
1µm. The polished samples then were coated by a layer of carbon (Q150TE, Quorum
Technologies Ltd., UK) shown in Fig.S1 before install the vacuum chamber of
electron micro-probe.
Quantitative chemical analysis was performed by a field emission electron micro
probe (FE-EPMA: JEOL JXA-8500F) equipped with five wave-length dispersive
spectrometers (WDS) at the Institute of Earth Sciences, Academia Sinica in Taipei.
3
Secondary- and back-scattered electron images were used to guide the analysis
positions. A focused beam was operated for quantitative analysis at an acceleration
voltage of 25 kV with a beam current of 10 nA. The measured X-ray intensities were
corrected by metal Phi-Rho-Z method using the standard calibration of pure metal of
Lα-lines of silver, tin, antimony and tellurium.
X-rays overlap among Ag, Sn, Sb
and Te were considered and interference intensities were corrected during the standard
intensity calibrations. Peak counting and both upper and lower baselines are counted
for 20 sec and 10 sec, respectively. Quantitative line profiles were applied for
representative phases at 10 μm intervals.
Elemental distribution (mapping) analysis was also made by FE-EPMA. A
focused beam was used at an acceleration voltage of 25 kV with a beam current of 20
nA. X-ray intensities were counted for 0.025 sec at the intervals of 0.05, 1 and 2 µm
with the X-Y stage driving.
4
FIG. S3 shows
FIG. S4
EPMA for AgSb0.95Sn0.05Te2 sample.
shows EPMA for AgSb0.93Sn0.07Te2 sample.
5
Carrier concentration (nH)
FIG. S5
Temperature dependence of Hall concentration of Ag(Sb1-xSnx)Te2 samples.
Calculation of Effective mass (m*)
The Seebeck coefficient of metals or degenerate semiconductors, with
the assumption of a parabolic band and energy independent scattering, can be
expressed as1, 2
2
8𝜋 2 kB2 𝑇 ∗ 𝜋 3
α =
𝑚 ( )
3𝑞ℎ2
3𝑛
(1)
where n is the carrier concentration, kB is the Boltzmann constant, q is the electronic
charge, h is the Planck constant, and m* is the effective mass.
6
Specific heat capacity (Cp)
FIG. S6 Temperature dependence of
heat capacity of Ag(Sb1-xSnx)Te2 samples.
Specific heat Cp was determined by using a differential scanning calorimeter (DSC,
NETZSCH, STA 449, heating rate 10 K min-1 and sample mass 25mg). The measured
specific heat values are consistent with each other for the samples. Supplementary Fig
S5 shows the measured representative specific heat values. Based on the specific heat
data, the results closely match the literature 3 value (Cp ~ 0.205 Jg-1K-1) of AgSbTe2.
7
Thermal stability of AgSb0.97Sn0.03Te2 sample
FIG. S7
Temperature dependences thermo-cycle of (a) electrical conductivity, (b)
Seebeck coefficient, (c) thermal diffusivity, and (d) thermoelectric figure of merit ZT
for Ag(Sb0.97Sn0.03)Te2 sample.
References
1
S. Y. Wang, W. J. Xie, H. Li, X. F. Tang, Intermetallics. 19, 1024 (2011).
2
J. P. Heremans, V. Jovovic, E. S.Toberer, A. Saramat, K. Kurosaki, A.
Charoenphakdee,
3
S. Yamanaka, G. J. Snyder, Science. 321, 554 (2008).
D. T. Morelli, V. Jovovic, J. P. Heremans, Phys. Rev. Lett.101, 035901 (2008).
8