Who discovered the chemical element yttrium?

Johan Gadolin (Åbo, Finland, 5 June 1760 – Wirmo, Finland, 15 August 1852) was a Finnish chemist, physicist and mineralogist. Gadolin discovered a "new earth" containing the first rare-earth compound yttrium, which was later determined to be a chemical element. He is also considered the founder of Finnish chemistry research, as the second holder of the Chair of Chemistry at the Royal Academy of Turku (or Åbo Kungliga Akademi). Gadolin was ennobled for his achievements and awarded the Order of Saint Vladimir and the Order of Saint Anna.

Yttrium is a chemical element with the symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a "rare-earth element". Yttrium is almost always found in combination with lanthanide elements in rare-earth minerals, and is never found in nature as a free element. Yttrium-89 is the only stable isotope, and the only isotope found in the Earth's crust.

Its major applications include hosts for red phosphors for fluorescent lamps, colour displays, and TV screens that use cathode-ray tubes. Yttrium iron garnet is used for microwave filters, radars, communications, and synthetic gems; and yttrium oxide-stabilized cubic zirconia is used in oxygen sensors, structural ceramics, thermal barrier coatings, and synthetic diamonds. It is also used in high-temperature superconducting ceramics. Its compounds are used in optical glasses and as catalysts.