Neptunium crystal structure

Initially, the only means of obtaining elements higher than uranium was by a-particle bombardment of uranium in the cyclotron, and it was by this means that the first, exceedingly minute amounts of neptunium and plutonium were obtained. The separation of these elements from other products and from uranium was difficult methods were devised involving co-precipitation of the minute amounts of their salts on a larger amount of a precipitate with a similar crystal structure (the carrier ). The properties were studied, using quantities of the order of 10 g in volumes of... 

Zachariasen, W. H. X-Ray Diffraction Studies of Fluorides of Plutonium and Neptunium. Chemical Identity and Crystal Structure. In G. T. Seaborg, J. J. Katz, and W. M. Manning (Eds.), The Transuranium Elements, National Nuclear Energy Series, Div. IV-14B, p. 1463. New York McGraw Hill Co. 1949. 

A lot of new coordination Np(V) complexes are still synthesized and several types of a novel CCB network have been found in their crystal structure [58-61]. Magnetic study is also performed about some neptunyl(+l) complexes [62], but there is no application of Np Mossbauer spectroscopy to them. Np Mossbauer spectroscopy is a very powerful and indispensable tool to study the electronic and the magnetic properties of neptunium complexes and will give several important information that cannot be provided with the magnetization measurement. Now Np Mossbauer spectroscopy is hardly performed due to the severe restrictions in handling transuranic materials and the output in this field is markedly reduced [63] however, many unsolved problems in this field that one should work on are left uncompleted. 

Actinium and thorium have no / electrons and behave like transition metals with a body-centered cubic structure of thorium. Neptunium and plutonium have complex, low-symmetry, room-temperature crystal structures and exhibit multiple phase changes with increasing temperature due to their delocalized 5/ electrons. For plutonium metal, up to six crystalline modifications between room temperature and 915 K exist. The / electrons become localized for the heavier actinides. Americium, curium, berkelium, and californium all have room-temperature, double hexagonal, close-packed phases and high-temperature, face-centered cubic phases. Einsteinium, the heaviest actinide metal available in quantities sufficient for crystal structure studies on at least thin films, has a face-centered cubic structure as typical for a divalent metal. 

Accommodation of metal atoms of widely differing ionic radii into the same overall structure creates interesting possibilities for the doping of metal ions into a common matrix for spectroscopic examination under nearly constant crystal field effects. For instance, observation of identical phases for zirconium and plutonium indicate that the zirconium compound would serve as a suitable matrix in which to isolate plutonium. Similarly, the appearance of identical phases for Th, U and Np makes possible the doping of uranium or neptunium into a thorium matrix. 

Bo.M2(P04)3. The thorium, uranium, and neptunium phosphates of general formula Bo 5M2(P04)3 with B = Be, Mg, Ca, Sr, Ba are characterized by extensive polymorphism [5,53,60,61,62,63,64]. As a result of thermal treatment of Mg, Ca, and Sr neptunium phosphates with unknown structures in an Ar + 5% H2 atmosphere, these compounds were established [5,53] as substances crystallizing with the monazite structure type. The authors of [35] have obtained a series of neptunium phosphates with an analogous composition by interaction between solutions of salts of divalent metals (Mg, or Ca, or Sr) with neptunium oxide Np02 and phosphoric acid followed by thermal stage-by-stage treatment... 

Neptunium dioxide, Np03, is the most stable of the neptunium oxides. It crystallizes with the fluorite structure of all the actinide dioxides, with a crystalline density of 11.14 g/cm . It can be formed from the thermal decomposition of other neptunium compounds, such as the hydroxide, the nitrate, or the oxalate, in the temperature range of 600 to 1000°C. High-fired NpOj can be dissolved in hot concentrated nitric acid containing small amounts of fluoride. 

Other substituted bis([8]annulene)actinide(IV) complexes of uranium,3-13 thorium,20 neptunium and plutonium have been prepared by the reaction of the substituted [8]annulene dianion with the appropriate actinide(IV) salt. X-ray diffraction data suggest that the alkyl-substituted neptunium(lV) and plutonium(IV) complexes are isomorphous with the corresponding uranium(IV) complex but none of the structures of these complexes has yet been determined from single crystal x-ray diffraction. 

Neptunium dioxide crystallizes in the cubic fluorite structure and magnetic measurements have been reported from 4 to 300 K [16,74,75]. There is a magnetic transition at 2S.4K. Above 60 K, the susceptibility follows the Curie-Weiss law pgn = 2.95-3.00/ig, 0 = —22 K). Below 10-12 K, the magnetic susceptibility becomes independent of temperature (xm = ... 

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