| Autor: |
Cross JN; Chemistry Division and the Plutonium Science and Manufacturing Directorate , Los Alamos National Laboratory , PO Box 1663 , Los Alamos , New Mexico , 87545 USA., Lee TH; Department of Physics and Astronomy , Rutgers University , Piscataway , New Jersey 08856 , USA., Kang CJ; Department of Physics and Astronomy , Rutgers University , Piscataway , New Jersey 08856 , USA., Yao YX; Department of Physics and Astronomy and Ames Laboratory , U.S. Department of Energy , Iowa State University , Ames , Iowa 50011 , USA., Cary SK; Chemistry Division and the Plutonium Science and Manufacturing Directorate , Los Alamos National Laboratory , PO Box 1663 , Los Alamos , New Mexico , 87545 USA., Stritzinger JT; Chemistry Division and the Plutonium Science and Manufacturing Directorate , Los Alamos National Laboratory , PO Box 1663 , Los Alamos , New Mexico , 87545 USA., Polinski MJ; Department of Chemistry and Biochemistry , Bloomsburg University of Pennsylvania , Bloomsburg , Pennsylvania 17815 , USA., McKinley CD; Department of Chemistry and Biochemistry , Florida State University , 95 Chieftan Way, 310 DLC , Tallahassee , Florida 32306 , USA . Email: albrecht-schmitt@chem.fsu.edu., Albrecht Schmitt TE; Department of Chemistry and Biochemistry , Florida State University , 95 Chieftan Way, 310 DLC , Tallahassee , Florida 32306 , USA . Email: albrecht-schmitt@chem.fsu.edu., Lanata N; Department of Physics and Astronomy , Aarhus University , 8000 , Aarhus C , Denmark . Email: lanata@phys.au.dk. |
| Abstrakt: |
A series of trivalent f-block tungstates, MW 2 O 7 (OH)(H 2 O) (M = La, Ce, Pr, Nd, and Pu) and AmWO 4 (OH), have been prepared in crystalline form using hydrothermal methods. Both structure types take the form of 3D networks where MW 2 O 7 (OH)(H 2 O) is assembled from infinite chains of distorted tungstate octahedra linked by isolated MO 8 bicapped trigonal prisms; whereas AmWO 4 (OH) is constructed from edge-sharing AmO 8 square antiprisms connected by distorted tungstate trigonal bipyramids. PuW 2 O 7 (OH)(H 2 O) crystallizes as red plates; an atypical color for a Pu(iii) compound. Optical absorption spectra acquired from single crystals show strong, broadband absorption in the visible region. A similar feature is observed for CeW 2 O 7 (OH)(H 2 O), but not for AmWO 4 (OH). Here we demonstrate that these significantly different optical properties do not stem directly from the 5f electrons, as in both systems the valence band has mostly O-2p character and the conduction band has mostly W-5d character. Furthermore, the quasi-particle gap is essentially unaffected by the 5f degrees of freedom. Despite this, our analysis demonstrates that the f-electron covalency effects are quite important and substantially different energetically in PuW 2 O 7 (OH)(H 2 O) and AmWO 4 (OH), indicating that the optical gap alone cannot be used to infer conclusions concerning the f electron contribution to the chemical bond in these systems. |
