Formation and Control of Thermoelectric Composites At the Nanoscale

Many new high efficiency thermoelectric materials are multi-phase composites at the nanometer scale.  These include materials such as PbTe alloys, and recently Zn4Sb3, which contain small ~10nm nanoparticles that can be difficult to control.  Typically the goal is to reduce the lattice thermal conductivity of the matrix by scattering phonons at the interfaces of the particles.  Thus it is not the small size of the particles but the spacing between particles that matter.  We have found that in PbTe with large (~50nm – 200nm) nanoparticles of Ag₂Te high zT ~ 1.5 can be obtained through the independent control of thermal conductivity reducing Ag₂Te large nanoparticles and electronic doping with La.

In general, because electrons are also scattered, a net improvement in thermoelectric efficiency will depend strongly on the spacing, size, shape, orientation and interfacial properties of the particles. At Caltech we have extensively studied the formation and control of composite microstructure in PbTe-Sb₂Te₃, identifying three distinct mechanisms for forming composites and controlling the characteristic length scales down to the nanometer scale. The coherent interfaces of these composites may help retain high carrier mobility.

 [1] G. J. Snyder, E. S. Toberer. Nature Materials 7, p 105 - 114 (2008).

[2] D.L. Medlin and G.J. Snyder "Interfaces in Bulk Thermoelectric Materials" Current Opinion in Colloid & Interface Science (2009)

[3] Yanzhong Pei, Jessica Lensch-Falk, Eric S. Toberer, Douglas L. Medlin, and G. Jeffrey Snyder “High Thermoelectric Performance in PbTe due to Large Nanoscale Ag₂Te Precipitates and La Doping” Advanced Functional Materials 21, 241 (2011)