Supplementary Information

Low Thermal Conductivity and High Thermoelectric Performance in In4Se3-x with Phase-Separated Indium Inclusions

Pankaj Kumar Rawat[1], Hwanjoo Park, Junphil Hwang, and Woochul Kim,[2]

School of Mechanical Engineering, Yonsei University, Seoul 120-749, Korea

Clarification on choosing In4Se2.95 stoichiometry for the investigations

At the start of the investigations, attempts were made to synthesize In4Se3-x with higher In:Se ratio. However, excess indium in such stoichiometries was found to be expelled during ball-milling and hot-pressing, which thus indicated deviation from the originally chosen stoichiometry towards lower In:Se ratio in final compound i.e., In4Se3-x. After several trials of synthesis, we came across to the stoichiometry i.e. In4Se2.95, in which no such discharge of excess indium was observed.

Basically, in the present investigation, we intended to study thermoelectric transport parameters in stoichiometrically stabilized In4Se3-x with indium inclusions (which remain within the material system after optimizing the In:Se ratio to stop discharge of indium metal from In4Se3-x).

Measured transport properties in S48 (shown below with measured transport properties in S24)

Figure S1. Comparative representation of temperature dependent (a) resistivity, (b) thermopower and (c) thermal conductivity in S24 and S48.

Calculated Cp for In4Se3

Figure S2. Calculated Cp for In4Se3.

EDEX Measurement

To ensure the stability of the stoichiometry In4Se2.95 EDEX measurement were performed for untreated and heat treated samples as shown below:

Figure S3. SEM image of untreated sample and corresponding EDEX.

Figure S4. SEM image of heat-treated sample and corresponding EDEX.

There were no noticeable change observed in In:Se ratio in the samples.

TEM Studies

The TEM studies were conducted to investigate the size distribution of the indium precipitates in In4Se3-x matrix. The darker contrast in Figure R5 depicts indium metal precipitates in In4Se3-x matrix, as the former has higher unit cell density than that of the later. TEM micrographs of both the samples (a) untreated and (b) heat treated shows nano-range hierarchical distribution of metallic indium in the host matrix. Such hierarchical distribution of particles is well known for scattering of phonons of wide frequency range and thus for the significant reduction in the thermal conductivity (Reference: K. Biswas, J. He, I. D. Blum, Chun-I Wu, T. P. Hogan, D. N. Seidman, V. P. Dravid and M. G. Kanatzidis, Nature, Vol. 489, pp. 414-418).

Figure S5. TEM image of (a) untreated, and (b) heat-treated sample.

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[1] Present Address: Science and Engineering Research Board, Vasant Kunj, New Delhi 110070, India

[2] To whom correspondence should be addressed: