Editing Terbium (section)

=== Physical properties ===
Terbium is a silvery-white [[rare earth element|rare earth]] [[metal]] that is [[malleable]], [[ductile]] and soft enough to be cut with a knife.<ref name="CRC" /> It is relatively stable in air compared to the more reactive lanthanides in the first half of the lanthanide series.<ref>{{cite web| url = http://www.elementsales.com/re_exp/index.htm |title = Rare-Earth Metal Long Term Air Exposure Test| access-date = 2009-05-05}}</ref> Terbium exists in two crystal [[allotropy|allotropes]] with a transformation temperature of 1289&nbsp;°C between them.<ref name="CRC" /> The 65 electrons of a terbium atom are arranged in the [[electron configuration]] [Xe]4f<sup>9</sup>6s<sup>2</sup>. The eleven 4f and 6s electrons are [[valence electron|valence]]. Only three electrons can be removed before the nuclear charge becomes too great to allow further ionization, but in the case of terbium, the stability of the half-filled [Xe]4f<sup>7</sup> configuration allows further ionization of a fourth electron in the presence of very strong oxidizing agents such as [[fluorine]] gas.<ref name="CRC" />

The terbium(III) cation (Tb<sup>3+</sup>) is brilliantly [[Fluorescence|fluorescent]], in a bright lemon-yellow color that is the result of a strong green [[emission line]] in combination with other lines in the orange and red. The yttrofluorite variety of the mineral [[fluorite]] owes its creamy-yellow fluorescence in part to terbium. Terbium easily oxidizes, and is therefore used in its elemental form specifically for research. Single terbium atoms have been isolated by implanting them into [[fullerene]] molecules. Trivalent [[europium]] (Eu<sup>3+</sup>) and Tb<sup>3+</sup> ions are among the lanthanide ions that have garnered the most attention because of their strong luminosity and great color purity.<ref>V.B. Taxak, R. Kumar, J.K. Makrandi, S.P. Khatkar Displays, 30 (2009), pp. 170–174</ref><ref>{{cite journal|last1=Shimada|first1=T.|last2=Ohno|first2=Y.|last3=Okazaki|first3=T.|last4=Sugai|first4=T.|last5=Suenaga|first5=K.|last6=Kishimoto|first6=S.|last7=Mizutani|first7=T.|last8=Inoue|first8=T.|last9=Taniguchi|first9=R.|last10=Fukui|display-authors=3 | first10=N.|last11=Okubo | first11=H.|last12=Shinohara | first12=H.|title=Transport properties of C<sub>78</sub>, C<sub>90</sub> and Dy@C<sub>82</sub> fullerenes – nanopeapods by field effect transistors|journal=Physica E: Low-dimensional Systems and Nanostructures|year=2004|volume=21|issue=2–4|pages=1089–1092|doi=10.1016/j.physe.2003.11.197|bibcode = 2004PhyE...21.1089S}}</ref>

Terbium has a simple [[ferromagnetic]] ordering at temperatures below 219&nbsp;K. Above 219&nbsp;K, it turns into a [[Helimagnetism|helical antiferromagnetic]] state in which all of the atomic moments in a particular [[basal plane]] layer are parallel and oriented at a fixed angle to the moments of adjacent layers. This antiferromagnetism transforms into a disordered [[paramagnetic]] state at 230&nbsp;K.<ref>{{cite journal| author =Jackson, M. | title =Magnetism of Rare Earth| url =http://www.irm.umn.edu/quarterly/irmq10-3.pdf | journal = The IRM Quarterly | volume =10| issue = 3| page = 1| date = 2000}}</ref>