The effect of nanostructuring on thermoelectric transport properties of p-type higher manganese silicide MnSi1.73

Abstract

Higher manganese silicide (HMS) alloys have a complex band structure with multiple valleys close to the conduction and valence band edges, which complicates the analysis of their electronic transport properties. We present a semi-classical two-band model that can describe the charge carrier and phonon transport properties of p-type HMS in crystalline and bulk nanostructured forms. The effect of grain boundaries is modeled with an interface potential scattering for charge carriers and diffusive and refractive scattering for phonons. A unique set of effective masses and acoustic phonon deformation potentials are introduced that can explain both electrical and thermal transport properties versus temperature. The acoustic phonon and ionized impurity scatterings for charge carriers and phonon-phonon, point defect, and electronphonon scattering mechanisms for phonons are included in the model. The simplicity of the presented model would be valuable especially for practical purposes. The thermoelectric transport properties of nanostructured HMS were calculated versus grain size and it was shown that even though bulk nanostructuring of HMS enhances thermoelectric performance, it is not sufficient to enhance considerably the figure-of-merit.

Molybdenum, Tungsten, and Aluminium Substitution for Enhancement of the Thermoelectric Performance of Higher Manganese Silicides

“…1 A variety of work has been conducted on tuning the transport properties of HMS by substitution or doping, [4][5][6][7][8][9][10][11][12][13][14] compositing, [15][16][17] and nanostructuring. 18,19 For substitution at Si sites, the highest ZT values obtained were 0.6 at 833 K and 0.65 at 850 K for Ge and Al-doped polycrystalline HMS, respectively. 4,7 Material containing 3 at.% and 5 at.% chromium substitution at Mn sites was reported to reach the highest ZT of approximately 0.6 at 850 K. 14 Recently, multiple simultaneous substitution of HMS systems has attracted renewed interest.…”

Twisting phonons in complex crystals with quasi-one-dimensional substructures

“…Because low-frequency phonons with relatively long mean free path still makes considerable contribution to the thermal conductivity in HMS crystals according to a combined low-frequency phonon and high-frequency diffuson model, our calculation suggests that glass-like thermal conductivity is achievable by introducing grain boundary scattering with a length scale of about 10 nm. As the charge carrier mean free path of HMS is estimated to be about 1-2 nm based on a two band semi-classical model 12 , it is expected that the electrical properties of HMS would not be affected significantly by reducing the grain size to 10 nm. Therefore, a ZT larger than 1 is possible by nanostructuring HMS, as a ZT of 0.6-0.7 has been achieved in doped samples with grain size of several micrometres 13,14,16 .…”

“…In contrast to most state-of-the-art thermoelectric materials such as lead telluride (PbTe), bismuth telluride (Bi 2 Te 3 ) and silicon germanium (SiGe), which contain rare, relatively costly, or toxic elements, HMS is made of two nontoxic elements that are abundant in the earth's crust. The combination of such features has continued to drive the interest to better understand and further enhance the thermoelectric properties of HMS [11][12][13][14][15][16][17] .…”

Comparison of thermoelectric properties of nanostructured Mg2Si, FeSi2, SiGe, and nanocomposites of SiGe–Mg2Si, SiGe–FeSi2

“…6 Although nanostructuring of some bulk materials such as BiSbTe, 7 Si, 8 SiGe, 9 and PbSrTe 10 showed significant improvement in ZT, similar trend was not observed in some other materials like Mg 2 Si, 11,12 FeSi 2 13 and MnSi 1.7 . 14,15 Multiphase composite materials have been also considered for thermoelectric applications. Thermoelectric properties of a composite material was conceptually studied by Straley in 1981 16 and later by Bergman and Levy in 1991, 17 where they claimed that the ZT of a two-component composite material can never exceed the ZT of each individual component.…”