Thermoelectric heat pumps exploit this phenomenon, as do thermoelectric cooling devices found in refrigerators. A Peltier cooler can also be used as a thermoelectric generator. The device relies on the Thermoelectric effect using Peltier tiles. It is also used as a thermal power source in radioisotope thermoelectric generator power packs. Iridium radioisotopes are used in some radioisotope thermoelectric generators. Their outputs are not functions of temperature differences as are thermoelectric and thermionic converters. Another use is as a carrier of strontium-90 radioisotope in radioisotope thermoelectric generators. Nuclear decay processes are used in niche applications such as radioisotope thermoelectric generators. LaO is an ingredient for the manufacture of piezoelectric and thermoelectric materials. Therefore, semiconductors are ideal thermoelectric materials. As with all thermoelectric plants, nuclear power plants need cooling systems. Electrical power is supplied by three MHW-RTG radioisotope thermoelectric generators (RTGs). Sr has been used as a power source for radioisotope thermoelectric generators (RTGs). Bismuth telluride (BiTe) and lead telluride are working elements of thermoelectric devices. New high-performance materials for thermoelectric cooling are being actively researched.