Nanostructuring and thermoelectric properties of bulk N-type Mg₂Si

Abstract

Preparation and thermoelectric properties of nanostructured n-type Mg₂Si bulk materials were reported. Nanosized Mg₂Si powder was obtained by mechanical milling of the microsized Mg₂Si powder prepared by solid-state reaction. The bulk materials with 30 nm and 5 µm were prepared by spark plasma sintering of the nanosized and microsized Mg₂Si powder, respectively. Both the samples show n-type conduction and the Seebeck coefficient of the sintered samples increase determinately with the grain size decrease from 5 µm to 30 nm. On the other hand, the electrical and thermal conductivity decrease with the decrease of grain size. Accordingly, decreasing their grain size increases their thermoelectric-figure-of-merit. A maximum thermoelectric figure of merit of 0.36 has been obtained for the nanostuctured Mg₂Si sample at 823 K, which is 38% higher than that of microsized Mg₂Si bulk materials and higher than results of other literatures. It could be expected that the properties of the nanocomposites could be further improved by doping optimization.

Keywords

emiconductor / thermoelectric effects / Mg₂Si / nanostructuring

References

[1] Jun-ichi T, Hiroyasu K. Thermoelectric Properties of Sb-doped Mg₂Si Semiconductors[J]. Intermetallics, 2007, (15): 1202–1207

[2] Zhang L. M., Gang Y. G. Synthesis of Mg₂Si_1−xGe_x Thermoelectric Compound by Solid Phase Reaction[J]. Mater. Sci. Eng B, 2001, 86: 195-199.

[3] Yoshinaga M., Iida T. Bulk Crysta Growth of Mg₂Si by the Vertical Bridgmam Method[J]. Thin Solid Film, 2004, 461: 86-89.

[4] Joseph P. H., Christopher M. T., Donald T. Morelli, Thermopower Enhancement in PbTe with Pb Precipitates [J]. J. Appl. Phys., 2005, 98: 063703

[5] Martin J., Nolas G. S. PbTe Nanocomposites Synthesized from PbTe Nanocrystals [J]. Appl. Phys. Lett., 2007, 90: 222-112.

[6] Joseph P. H., Christopher M. T., Donald T. M. Thermopower Enhancement in Lead Telluride Nanostructures[J]. Physical Review B., 2004, 70: 115334

[7] Mi J. L., Zhao X. B. Improved Thermoelectric Figure of Merit in N-type CoSb₃ Based Nanocomposites [J]. Appl. Phys. Lett., 2007, 91: 172116

[8] Bhandari C M. Thermoelectric Transport Theory[M]. CRC Handbook of Thermoelectrics, edited by D M Rowe, Chap.1: 27

[9] Wang L., Qin X. Y. The Effect of Mechanical Milling on the Formation of Nanocrystalline Mg₂Si through Solid-state Reaction [J]. Scripta Materialia, 2003, 49: 243-248.

[10] Riffel M., Schilz J. Mechanical Alloying of Mg₂Si [J]. Scripta Metallurgica et Materialia, 1995, 32(12): 1951-1956.

[11] Wang L., Qin X. Y. Fabrication and Mechanical Properties of Bulk Nanocrystalline Intermetallic Mg₂Si [J]. Material Science and Engineering A, 2007, 459: 216-222.

[12] Lee C. H., Lee S. H. Fabrication of Mg₂Si Thermoelectric Materials by Mechanical Alloying and Spark Plasma Sintering Process[J]. J. Nanosci. Nanotech., 2006, 6: 3429-3432.

[13] Riffel M, J Schilz. Influence of Production Parameters on the Thermoelectric Properites of Mg₂Si[C]. 16^th International Conference on Thermoelectrics, 1997: 283–286

[14] Mi J. L., Zhu T. J., Zhao X. B. Nanostructuring and Thermoelectric Properties of Bulk Skutterudite Compound CoSb₃ [J]. J. Appl. Phys., 2007, 101: 054314

[15] Kishimoto K., Koyanagi T. Preparation of Sintered Degenerate N-type PbTe with a Small Grain Size and its Thermoelectric Properties [J]. J. Appl. Phys., 2002, 92: 2544

[16] Han L., Tang X. F., Su X. L., Zhang Q. J. Preparation and Thermoelectric Properties of High-performance Sb Additional Yb_0.2Co₄Sb_12+y Bulk Materials with Nanostructure [J]. Applied Physics Letters, 2008, 92: 202114

[17] Bhandari C M. M inimizing the Thermal Conductivity[M]. CRC Handbook of Thermoelectrics, edited by D M Rowe, Chap. 1: 55

[18] Nan C. W., Birringer R. Determining the Kapitza Resistance and the Thermal Conductivity of Polycrystals: A Sample Model[J]. Phys. Rev. B, 1998, 57: 8264

[19] Ni H. L., Zhao X. B. Synthesis and Thermoelectric Properties of Bi₂Te₃ Based Nanocomposites [J]. J. Alloys Compd., 2005, 397: 317-321.

[20] Jiang H. Y. Study on the Solid-state Reaction Synthesis, Preparation and Thermoelectric Properties of Mg-Si Based Compounds[D], 2003 Wuhan Wuhan University of Technology 73