(en) Pieter Thyssen, Koen Binnemans, Hisanori Shinohara, Yahachi Saito, Lubomir D. Gulay, Marek Daszkiewicz, Chun-Hua Yan, Zheng-Guan Yan et Ya-Ping Du, Handbook on the Physics and Chemistry of Rare Earths, Amsterdam, The Netherlands, North Holland, (ISBN978-0-444-53590-0, lire en ligne), p. 66