Observation of valence band crossing: the thermoelectric properties of CaZn2Sb2–CaMg2Sb2 solid solution

There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

Abstract

Using an effective mass model, the changing valence band character of CaZn ₂Sb ₂–CaMg ₂Sb ₂ solid solution was probed along with the thermoelectric properties.

Abstract

CaAl ₂Si ₂ type Zintl phases have long been known to be promising thermoelectric materials. Here we report for the first time on the thermoelectric properties of CaMg ₂Sb ₂ along with the transport properties of CaZn ₂Sb ₂–CaMg ₂Sb ₂ solid solution. The charge carrier tuning in this system was carried out by substituting divalent Ca ²⁺ with monovalent Na ⁺. To check a possible band convergence, we applied an effective mass analysis to our samples and found an abrupt doubling of the samples' effective masses as the composition switches from Zn-rich to Mg-rich. We further analyzed the effect that alloy scattering plays in the lattice thermal conductivity of our samples with a Modified Klemens model. We showed that the reduction seen in the lattice thermal conductivity of the alloyed samples can be well explained based on the mass difference of Mg and Zn in the poly-anionic metal site. Our best p-doped sample with a composition of Ca _.99Na _.01MgZnSb ₂ displays a relatively high peak zT of 0.87 at 850 K.

Related collections

Most cited references 36

Record: found
Abstract: found
Article: not found

Complex thermoelectric materials.

G Jeffrey Snyder, Eric Toberer (2008)

Thermoelectric materials, which can generate electricity from waste heat or be used as solid-state Peltier coolers, could play an important role in a global sustainable energy solution. Such a development is contingent on identifying materials with higher thermoelectric efficiency than available at present, which is a challenge owing to the conflicting combination of material traits that are required. Nevertheless, because of modern synthesis and characterization techniques, particularly for nanoscale materials, a new era of complex thermoelectric materials is approaching. We review recent advances in the field, highlighting the strategies used to improve the thermopower and reduce the thermal conductivity.

0 comments Cited 1982 times – based on 0 reviews      Review now

Bookmark

Record: found
Abstract: found
Article: not found

Convergence of electronic bands for high performance bulk thermoelectrics.

Yanzhong Pei, Xiaoya Shi, Aaron D LaLonde … (2011)

Thermoelectric generators, which directly convert heat into electricity, have long been relegated to use in space-based or other niche applications, but are now being actively considered for a variety of practical waste heat recovery systems-such as the conversion of car exhaust heat into electricity. Although these devices can be very reliable and compact, the thermoelectric materials themselves are relatively inefficient: to facilitate widespread application, it will be desirable to identify or develop materials that have an intensive thermoelectric materials figure of merit, zT, above 1.5 (ref. 1). Many different concepts have been used in the search for new materials with high thermoelectric efficiency, such as the use of nanostructuring to reduce phonon thermal conductivity, which has led to the investigation of a variety of complex material systems. In this vein, it is well known that a high valley degeneracy (typically ≤6 for known thermoelectrics) in the electronic bands is conducive to high zT, and this in turn has stimulated attempts to engineer such degeneracy by adopting low-dimensional nanostructures. Here we demonstrate that it is possible to direct the convergence of many valleys in a bulk material by tuning the doping and composition. By this route, we achieve a convergence of at least 12 valleys in doped PbTe(1-x)Se(x) alloys, leading to an extraordinary zT value of 1.8 at about 850 kelvin. Band engineering to converge the valence (or conduction) bands to achieve high valley degeneracy should be a general strategy in the search for and improvement of bulk thermoelectric materials, because it simultaneously leads to a high Seebeck coefficient and high electrical conductivity. ©2011 Macmillan Publishers Limited. All rights reserved