Metalloid silicon, germanium, arsenic, antimony, and tellurium are commonly recognised as metalloids. Depending on the author, one or more from selenium, polonium, or astatine are sometimes added to the list. Boron sometimes is excluded, by itself, or with silicon. Sometimes tellurium is not regarded as a metalloid. The inclusion of antimony, polonium, and astatine as metalloids has been questioned. Other elements are occasionally classified as metalloids. These elements include hydrogen, beryllium, nitrogen, phosphorus, sulfur, zinc, gallium, tin, iodine, lead, bismuth, and radon. The term metalloid has also been used for elements that exhibit metallic lustre and electrical conductivity, and that are
Application of silicon-germanium thermoelectrics in space exploration power applications. Application of silicon-germanium thermoelectrics in space exploration Silicon-germanium (SiGe) thermoelectrics have been used for converting heat into power in spacecraft designed for deep-space NASA missions since 1976. This material is used in the radioisotope thermoelectric generators (RTGs) that power "Voyager 1", "Voyager 2", "Galileo", "Ulysses", "Cassini", and "New Horizons" spacecraft. SiGe thermoelectric material converts enough radiated heat into electrical power to fully meet the power demands of each spacecraft. The properties of the material and the remaining components of the RTG contribute towards the efficiency of this thermoelectric conversion. Heavily doped semiconductors, such as silicon-germanium (SiGe) thermoelectric couples