Despite decades of specialty applications, thermoelectrics, a field that encompasses a collection of temperature-control and power generation technologies, remains obscure. The applications, such as miniature coolers that chill infrared detectors in night-vision systems and climate-control automobile seats, are enabled by a limited number of semiconductors that exhibit an unusual combination of properties. The list includes having good electrical but poor thermal conductivity, as well as exhibiting an electrical response to a temperature gradient. A greater variety of applications, including ones that generate electricity from waste heat, could result from discovery of new types of thermoelectric materials. A team led by chemist Kirill Kovnir of the University of California, Davis, has done just that. The group reports that Ba8Au16P30, a host-guest compound in which barium ions are trapped inside large gold-phosphorus polyhedral cages, exhibits unprecedentedly low lattice thermal conductivity (J. Am. Chem. Soc. 2013, DOI: 10.1021/ja4052679). The team attributes that property to the high mass of the gold atoms and the large number of crystal interfaces and defects, which inhibit heat transmission through the crystal’s lattice.