The term "piezoelectric" refers to those materials that generate electricity through the application of a pressure or physical force upon them. Conversely, the physical structure of these materials can be altered by the introduction of electricity.
Some piezoelectric compounds include quartz, gallium phosphate and aluminum nitride. The practical uses of piezoelectric materials include advanced sound sensors, the generation of high voltage electricity and sources of ignition. In 2014, scientists from the University of Houston demonstrated the ability of a one-atom-thick layer of graphene nitride to display piezoelectric properties. At about 1,000 times thinner than human hair, it is one of the thinnest possible piezoelectric materials.