Editing Curium (section)

===Physical===
[[File:Closest packing ABAC.png|thumb|Double-hexagonal close packing with the layer sequence ABAC in the crystal structure of α-curium (A: green, B: blue, C: red)]]
[[File:Cm(HDPA)3·H2O_PL_420_nm.jpg|220x124px|thumb|right|[[Photoluminescence]] of the Cm(HDPA)<sub>3</sub>·H<sub>2</sub>O crystal upon [[irradiation]] with 420&nbsp;nm light]]
A synthetic, radioactive element, curium is a hard, dense metal with a silvery-white appearance and physical and chemical properties resembling [[gadolinium]]. Its melting point of 1344&nbsp;°C is significantly higher than that of the previous elements neptunium (637&nbsp;°C), plutonium (639&nbsp;°C) and americium (1176&nbsp;°C). In comparison, gadolinium melts at 1312&nbsp;°C. Curium boils at 3556&nbsp;°C. With a density of 13.52&nbsp;g/cm<sup>3</sup>, curium is lighter than neptunium (20.45&nbsp;g/cm<sup>3</sup>) and plutonium (19.8&nbsp;g/cm<sup>3</sup>), but heavier than most other metals. Of two crystalline forms of curium, α-Cm is more stable at ambient conditions. It has a hexagonal symmetry, [[space group]] P6<sub>3</sub>/mmc, lattice parameters ''a''&nbsp;=&nbsp;365&nbsp;[[picometer|pm]] and ''c''&nbsp;=&nbsp;1182&nbsp;pm, and four [[formula unit]]s per [[unit cell]].<ref name="Milman">{{cite journal|last1=Milman|first1=V.|title=Crystal structures of curium compounds: an ab initio study|journal=Journal of Nuclear Materials|volume=322|issue=2–3|page=165|date=2003|doi=10.1016/S0022-3115(03)00321-0|bibcode=2003JNuM..322..165M|last2=Winkler|first2=B.|last3=Pickard|first3=C. J.}}</ref> The crystal consists of double-[[Close-packing of equal spheres|hexagonal close packing]] with the layer sequence ABAC and so is isotypic with α-lanthanum. At pressure >23&nbsp;[[Pascal (unit)|GPa]], at room temperature, α-Cm becomes β-Cm, which has [[Cubic crystal system|face-centered cubic]] symmetry, space group Fm{{overline|3}}m and lattice constant ''a''&nbsp;=&nbsp;493&nbsp;pm.<ref name = "Milman" /> On further compression to 43&nbsp;GPa, curium becomes an [[Orthorhombic crystal system|orthorhombic]] γ-Cm structure similar to α-uranium, with no further transitions observed up to 52&nbsp;GPa. These three curium phases are also called Cm I, II and III.<ref>Young, D. A. [https://books.google.com/books?id=F2HVYh6wLBcC&pg=PA227 Phase diagrams of the elements], University of California Press, 1991, {{ISBN|0-520-07483-1}}, p. 227</ref><ref>{{cite journal|last1=Haire|first1=R.|last2=Peterson|first2=J.|last3=Benedict|first3=U.|last4=Dufour|first4=C.|last5=Itie|first5=J.|title=X-ray diffraction of curium-248 metal under pressures of up to 52 GPa|journal=Journal of the Less Common Metals|volume=109|issue=1|page=71|date=1985|doi=10.1016/0022-5088(85)90108-0}}</ref>

Curium has peculiar magnetic properties. Its neighbor element americium shows no deviation from [[Curie–Weiss law|Curie-Weiss]] [[paramagnetism]] in the entire temperature range, but α-Cm transforms to an [[Antiferromagnetism|antiferromagnetic]] state upon cooling to 65–52&nbsp;K,<ref>{{cite journal|last1=Kanellakopulos|first1=B.|title=The magnetic susceptibility of Americium and curium metal|journal=Solid State Communications|volume=17|issue=6|page=713|date=1975|doi=10.1016/0038-1098(75)90392-0|bibcode = 1975SSCom..17..713K|last2=Blaise|first2=A.|last3=Fournier|first3=J. M.|last4=Müller|first4=W. }}</ref><ref>{{cite journal|last1=Fournier|first1=J.|title=Curium: A new magnetic element|journal=Physica B+C|volume=86–88|page=30|date=1977|doi=10.1016/0378-4363(77)90214-5|bibcode = 1977PhyBC..86...30F|last2=Blaise|first2=A.|last3=Muller|first3=W.|last4=Spirlet|first4=J.-C. }}</ref> and β-Cm exhibits a [[Ferrimagnetism|ferrimagnetic]] transition at ~205&nbsp;K. Curium pnictides show [[Ferromagnetism|ferromagnetic]] transitions upon cooling: <sup>244</sup>CmN and <sup>244</sup>CmAs at 109&nbsp;K, <sup>248</sup>CmP at 73&nbsp;K and <sup>248</sup>CmSb at 162&nbsp;K. The lanthanide analog of curium, gadolinium, and its pnictides, also show magnetic transitions upon cooling, but the transition character is somewhat different: Gd and GdN become ferromagnetic, and GdP, GdAs and GdSb show antiferromagnetic ordering.<ref>Nave, S. E.; Huray, P. G.; Peterson, J. R. and Damien, D. A. [http://www.osti.gov/bridge/purl.cover.jsp;jsessionid=ECF73C70531D64E8B663048ECE8C10F9?purl=/6263633-jkoGGI/ Magnetic susceptibility of curium pnictides], Oak Ridge National Laboratory</ref>

In accordance with magnetic data, electrical resistivity of curium increases with temperature – about twice between 4 and 60&nbsp;K – and then is nearly constant up to room temperature. There is a significant increase in resistivity over time (~{{val|10|u=μΩ·cm/h}}) due to self-damage of the crystal lattice by alpha decay. This makes uncertain the true resistivity of curium (~{{val|125|u=μΩ·cm}}). Curium's resistivity is similar to that of gadolinium, and the actinides plutonium and neptunium, but significantly higher than that of americium, uranium, [[polonium]] and [[thorium]].<ref name="res" />

Under ultraviolet illumination, curium(III) ions show strong and stable yellow-orange [[fluorescence]] with a maximum in the range of 590–640&nbsp;nm depending on their environment.<ref name="denecke">{{cite journal|last1=Denecke|first1=Melissa A.|last2=Rossberg|first2=André|last3=Panak|first3=Petra J.|last4=Weigl|first4=Michael|last5=Schimmelpfennig|first5=Bernd|last6=Geist|first6=Andreas|title=Characterization and Comparison of Cm(III) and Eu(III) Complexed with 2,6-Di(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine Using EXAFS, TRFLS, and Quantum-Chemical Methods|journal=Inorganic Chemistry|volume=44|issue=23|date=2005|pmid=16270980|doi=10.1021/ic0511726|pages=8418–8425}}</ref> The fluorescence originates from the transitions from the first excited state <sup>6</sup>D<sub>7/2</sub> and the ground state <sup>8</sup>S<sub>7/2</sub>. Analysis of this fluorescence allows monitoring interactions between Cm(III) ions in organic and inorganic complexes.<ref name="plb">Bünzli, J.-C. G. and Choppin, G. R. ''Lanthanide probes in life, chemical, and earth sciences: theory and practice'', Elsevier, Amsterdam, 1989 {{ISBN|0-444-88199-9}}</ref>