| About this Abstract |
| Meeting |
2011 Electronic Materials Conference
|
| Symposium
|
2011 Electronic Materials Conference
|
| Presentation Title |
B2, Ca3AlSb3 and Ca5Al2Sb6; Inexpensive, Non-Toxic Thermoelectric Materials
for Waste Heat Recovery |
| Author(s) |
Alex Zevalkink, Eric Toberer, Wolfgang Zeier, Espen Flage-Larsen, Jeff Snyder |
| On-Site Speaker (Planned) |
Alex Zevalkink |
| Abstract Scope |
Ca<SUB>3</SUB>AlSb<SUB>3</SUB> and Ca<SUB>5</SUB>Al<SUB>2</SUB>Sb<SUB>6</SUB> are Earth-abundant, non-toxic Zintl compounds, with promising thermoelectric properties. Both compounds have crystal structures consisting of infinite, parallel chains of corner sharing AlSb<SUB>3</SUB> tetrahedra, surrounded by calcium cations. However, the relative deficiency of calcium in Ca<SUB>5</SUB>Al<SUB>2</SUB>Sb<SUB>6</SUB> causes the formation of Sb-Sb bonds between the chains, which results in tetrahedral “ladders”. The structural complexity of Ca<SUB>3</SUB>AlSb<SUB>3</SUB> and Ca<SUB>5</SUB>Al<SUB>2</SUB>Sb<SUB>6</SUB> (26 and 28 atoms per unit cell, respectively) contributes to their extremely low lattice thermal conductivity, which approaches the amorphous limit at high temperatures (~0.6 W/mK at 1050 K). High temperature Hall and Seebeck measurements confirm that both compounds are charge-balanced semiconductors, as expected from Zintl charge-counting conventions. Optimization of electronic properties is achieved via control of the p-type carrier concentration through sodium doping. To first order, the high temperature electronic behavior of the doped samples can be well described by a single parabolic band model. Electronic structure calculations for Ca<SUB>3</SUB>AlSb<SUB>3</SUB> reveal a valence band edge containing nested parabolic bands, and dominated by Sb p states. A maximum zT of 0.8 and 0.6 is obtained at 1000 K for sodium-doped Ca<SUB>3</SUB>AlSb<SUB>3</SUB> and Ca<SUB>5</SUB>Al<SUB>2</SUB>Sb<SUB>6</SUB>, respectively. In both cases, we attribute the high thermoelectric efficiency to a combination of low lattice thermal conductivity and a band gap sufficiently large to delay the detrimental effect of minority carriers on the Seebeck coefficient until high temperatures. |
| Proceedings Inclusion? |
Undecided |