This element was discovered in 1923 by D. Coster and G. von Hevesey in Copenhagen, Denmark. The name comes from the Latin name of Copenhagen (Hainia).

Ionization energies
HfI 6.6 eV, HfII 14.9 eV, HfIII 23.3 eV.

Absorption lines of HfI
The equivalent width of HfI 3616 in the sun is 0.001.

Absorption lines of HfII
The equivalent width of HfII 3505(7) in the sun is 0.024. In one F 0Ib star, W(3399) = 0.008 (Reynolds et al. 1988).

Behavior in non-normal stars
HfI lines are enhanced in some Ba stars, which leads to large overabundances of the order of 0.5 - 1.0 dex (Lambert 1985, Smith 1984).

Hf has six stable isotopes, 12 short-lived isotopes and isomers and one isotope with a long half life. The stable ones are Hf 174, 176, 177, 178, 179 and 180. In the solar system they represent respectively 0.2%, 5%, 19%, 27%, 14% and 35% of all the Hf. The long-lived isotope Hf182 has a half life of 9 × 106 years, which could be useful for radioactive dating.

Hf isotopes can be produced by several nuclear processes. Hf174 is a pure p process and Hf176 a pure s process product. The other four (Hf 177-180) can be produced by both the r and the s process.

Published in "The Behavior of Chemical Elements in Stars", Carlos Jaschek and Mercedes Jaschek, 1995, Cambridge University Press.