AVS 61st International Symposium & Exhibition
    Actinides and Rare Earths Focus Topic Monday Sessions
       Session AC+AS+MI+SA+SS-MoM

Paper AC+AS+MI+SA+SS-MoM9
Hydrides of U-Mo and U-Zr Alloys: Structure and Electronic Properties

Monday, November 10, 2014, 11:00 am, Room 301

Session: Spectroscopy, Microscopy and Dichroism of Actinides and Rare Earths
Presenter: Ladislav Havela, Charles University, Czech Republic
Authors: L. Havela, Charles University, Czech Republic
M. Paukov, Charles University, Czech Republic
I. Tkach, Charles University, Czech Republic
D. Drozdenko, Charles University, Czech Republic
M. Cieslar, Charles University, Czech Republic
Z. Matej, Charles University, Czech Republic
Correspondent: Click to Email
When U metal (α-U) is exposed to H gas, it forms a stable hydride β-UH3. The lattice expansion stabilizes the ferromagnetic order with the Curie temperature around 170 K. The metastable form, α-UH3, could not be synthesized as a pure phase, and the admixture of β-UH3 did not allow to determine reliably its intrinsic magnetic properties. We have been testing the reaction to H exposure of γ-U (bcc), which was synthesized as a single phase by combination of Mo or Zr doping into U and ultrafast cooling. We found that such alloys need high H2 pressure and long exposure to absorb hydrogen. The products can be characterized by the formula UH3Mo(Zr)x. The hydrides with Mo have a structure corresponding to β-UH3 with grain size around 1 nm, i.e. almost amorphous. Its ordering temperatures increase to 200 K for UH3Mo0.18 and then decrease for higher Mo concentrations. The hydrides UH3Zrx exhibit the UH3 structure (bcc U lattice filled with H atoms). Their Curie temperature weakly decreases with increasing Zr concentration and the extrapolation to Zr-free state indicates TC = 170 K, i.e. identical to β-UH3. The results can be compared with numerous hydrides obtained by hydrogenation of U6X compounds (X = Mn, Fe, Co, Ni), all probably having similar magnetic properties. We present a detailed study of magnetic properties, electrical resistivity and specific heat. The structure characterization of initial alloys and the hydrides has been done by means of XRD, SEM with EBSD and TEM. The hydrides represent and new class of U materials, which exhibit, irrespective of details of composition or crystal structure, strong ferromagnetism with relatively very high ordering temperatures, quite surprising at materials at which the inter-U spacing does not exceed appreciably the Hill limit 340-360 pm. At last, the variations using double doping (both Mo and Zr) will be presented.