Ca₃AlSb₃: an inexpensive, non-toxic thermoelectric material for waste heat recovery

Abstract

Thermoelectric materials directly convert thermal energy into electrical energy, offering a promising solid-state solution for waste heat recovery. For thermoelectric devices to make a significant impact on energy and the environment the major impediments are the efficiency, availability and toxicity of current thermoelectric materials. Typically, efficient thermoelectric materials contain heavy elements such as lead and tellurium that are toxic and not earth abundant. Many materials with unusual structures containing abundant and benign elements are known, but remain unexplored for thermoelectric applications. In this paper we demonstrate, with the discovery of high thermoelectric efficiency in Ca 3 AlSb 3 , the use of elementary solid-state chemistry and physics to guide the search and optimization of such materials.

Thermoelectric Properties and Electronic Structure of the Zintl‐Phase Sr3AlSb3

“…6 We have previously reported exceptionally low κ L in several other chain-forming A 5 M 2 Sb 6 and A 3 MSb 3 compounds (A = Ca, Sr and M = Al, Ga, In). [15][16][17][18] The temperature dependence of κ L in Sr 5 Al 2 Sb 6 is very similar to these compounds, decreasing as 1/T with increasing temperature due to Umklapp scattering, and approaching the predicted minimum at high temperature. Because the unit cell size and average speed of sound of Sr 5 Al 2 Sb 6 (52 atoms, 2610 m s −1 ) are comparable to that of Sr 3 AlSb 3 (56 atoms, 2590 m s −1 ), κ L should be very similar in these two materials, despite their different structure types.…”

“…28 Structural differences between the A 5 Al 2 Sb 6 phases, in addition to the possible influence of the cation on the stability of acceptor defects (e.g., Sr vacancies and Zn substitution on Al site), could explain this disparity. In previous studies, Na 1+ on the Ca 2+ site was a successful dopant in both Ca 5 Al 2 Sb 6 and Ca 3 AlSb 3 compounds, 16,18 suggesting that similar substitutions may prove successful in increasing the carrier concentration in Sr 5 Al 2 Sb 6 .…”

“…For example, in the Zintl phase Ca 3 AlSb 3 , doping with Na on the Ca site was found to be more effective at increasing the p-type carrier concentration than substitution Zn on the Al site. 16 …”

“…By doping with Zn 2+ on the M 3+ site or Na 1+ on the A 2+ site, the charge carrier concentration of these compounds can be optimized, leading to figures of merit as high as zT = 0.9. [15][16][17][18] Among A 5 M 2 Sb 6 compounds, most form either the Ca 5 Al 2 As 6 or Ca 5 Al 2 Bi 6 structure type. 19,20 These structure types both contain infinite chains of corner-linked MSb 4 tetrahedra in which neighboring chains are linked by Sb-Sb bonds to form ladder-like anionic structures.…”

Intrinsically low thermal conductivity from a quasi-one-dimensional crystal structure and enhanced electrical conductivity network via Pb doping in SbCrSe3

“…The calculated results were similar to the value for BiCuSeO (2107 m s − 1 ), 48 larger than those of PbTe (1770 m s − 1 ), 51 and smaller than that of the Zintl chain compound Ca 3 AlSb 3 (2710 m s − 1 ). 55 Materials with a low Young`s modulus are considered to have 'soft' bonding, which results Intrinsically low thermal conductivity from a quasi-onedimensional crystal structure D Yang et al in slow phonon transport and thus a low lattice thermal conductivity. The calculated Young`s modulus 48 of SbCrSe 3 is 64 GPa, which is similar to those of the low lattice thermal conductivity compounds CdSb (55-60 GPa, 1590 m s − 1 , 1.0 W m − 1 K − 1 ) 9 and BiCuSeO (76.5 GPa, 2107 m s − 1 , 0.9 W m − 1 K − 1 ).…”