Reduced Grain Size and Improved Thermoelectric Properties of Melt Spun (Hf,Zr)NiSn Half-Heusler Alloys

Abstract

Half-Heusler thermoelectric materials Hf(/Zr)NiSn were prepared by levitation melting followed by melt-spinning to refine the boundary structures, and then they were consolidated by spark plasma sintering. X-ray diffraction analysis and scanning electron microscopy showed that single phased halfHeusler compounds without compositional segregation had been obtained. It was found that the thermoelectric properties, especially the thermal conductivity, depended strongly on the boundary structures. The melt-spinning samples with refined boundary structures had a lower thermal conductivity but a power factor comparable to that of the sample prepared by levitation melting, thus providing good thermoelectric properties.

Recent Advances in Nanostructured Thermoelectric Half-Heusler Compounds

“…For the two kinds of nanocomposites, there are also several different preparation methods for each of them. For example, nanoinclusions in a micro-scale HH matrix can be prepared by in-situ formation [79,80,106] as well as ex-situ mixing [71,77,78,107,108,109,110], and the nano-scale HH phase can be obtained by either ball milling [53,67,72,73,111] or melt spinning [74,112,113]. It is not our intent (which would be quite daunting) to cover all the possible preparation methods for HH nanocomposites in this article.…”

“…The inset in ( d ) is the high resolution TEM image of a nanophase samples. ( a ) and ( b ) reproduced with permission from Reference [74]. Copyright 2010, Springer.…”

“…Indeed, the nanostructuring approach significantly enhances the ZT values of HH nanocomposites by significantly reducing the lattice thermal conductivity [69,70,71,72,73,74,75,76,77,78]. However, more recently, it is reported that, in addition to the reduction in the lattice thermal conductivity, nanostructuring can also increase the power factor, PF , in some HH nanocomposites [79,80].…”

High performance Bi2Te3 nanocomposites prepared by single-element-melt-spinning spark-plasma sintering

“…5 FESEM images of SE-MS-Bi 2 Te 3 ribbon sample: a free surface and b contact surface nanocomposite TE materials, the characteristic length scale of at least one constituent is on the nanometer scale; the resulting classical and quantum size effects help ease the interdependence of those properties. Many nanocomposites achieved higher ZT than their traditional bulk counterparts, to name a few, PbTe-based alloys [35][36][37][38], filled CoSb 3 [39][40][41][42][43], half-Heusler [44][45][46][47][48][49], SiGe [50,51], and Bi 2 Te 3 -based compounds [52][53][54][55][56][57][58][59][60][61].…”

Effect of C and N Addition on Thermoelectric Properties of TiNiSn Half-Heusler Compounds

“…The XYZ structure is a MgAgAs type (space group F-43m), where X, Y, and Z atoms consist of three interpenetrating FCC sub-lattices by occupying the Wyckoff positions of 4b(1/2, 1/2, 1/2), every other 4c(1/4, 1/4, 1/4) position is empty. Based on calculations, half-Heusler compounds have a valence electron count (VEC) of 18 per stable unit cell, and show a band-gap in the range of 0~1.1 eV, which is suitable for mid-temperature applications of TE devices [ 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ].…”