Terbium is a chemical element with the symbol Tb and atomic number 65. It is a silvery-white, rare earth metal that is malleable, ductile, and soft enough to be cut with a knife.
Phase at STP： solid
Melting point： 1629 K (1356 °C, 2473 °F)
Boiling point： 3396 K (3123 °C, 5653 °F)
Density (near r.t.)： 8.23 g/cm3
when liquid (at m.p.)： 7.65 g/cm3
Heat of fusion： 10.15 kJ/mol
Heat of vaporization： 391 kJ/mol
Molar heat capacity： 28.91 J/(mol·K)
Terbium is used to dope calcium fluoride, calcium tungstate and strontium molybdate, materials that are used in solid-state devices, and as a crystal stabilizer of fuel cells which operate at elevated temperatures. As a component of Terfenol-D (an alloy that expands and contracts when exposed to magnetic fields more than any other alloy), terbium is of use in actuators, in naval sonar systems and in sensors.