Custom Doped Thermoelectrics

Thermoelectric materials with exceptional energy conversion properties can be prepared by way of a chemical doping procedure designed to customize the starting materials’ electronic structure, according to materials scientists at California Institute of Technology (Nature, DOI: 10.1038/nature09996). The work may lead to technology for converting waste heat—for example in automobile exhaust—to electricity with high enough efficiency to make such systems suitable for widespread application. Thermoelectric materials are endowed with a curious property that enables them to convert heat to electricity when a temperature difference develops across such a material. Similarly, an applied potential can heat or cool these materials. How well they facilitate this energy conversion is indicated by the so-called thermoelectric figure of merit, zT, which for applications ideally should be above 1.5. Today’s thermoelectric products feature materials based on PbTe and have zT values below 1.0. Most of the recent work aimed at boosting that value focuses on tailoring the materials’ nanostructures. Caltech’s Yanzhong Pei, G. Jeffrey Snyder, and coworkers chose instead to customize PbTe’s electronic structure by selectively doping it with sodium and selenium. That strategy led to Pb_0.98Na_0.02Te_{1– x}Se_x samples with unprecedented zT values as high as 1.8, they report.