NASA's latest rover on Mars depends on a sandwich of
semiconducting material that can turn heat into electricity. In
the case of Curiosity, the steady radioactive decay of plutonium
238 warms such thermoelectric material and turns roughly 4
percent of that heat into a steady flow of electrons. A similar
radioisotope thermoelectric generator (RTG) on the moon's Sea of
Tranquility is still working after decades, as are the RTGs in
the two Voyager spacecraft launched 35 years ago; such enduring
reliability is the main reason NASA employed the inefficient
technology. Now researchers have discovered a way to at least
double the efficiency of such power generators—suggesting that
thermoelectrics might find a home in applications outside of
aerospace and back here on Earth. The most common core of new
and old thermoelectrics is a compound called lead telluride.
When exposed to heat on only one side—whether it be from a
radioactive isotope or another source—it will induce an electric
current as long as the temperatur