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Theoretical prediction of some layered Pa 2 O 5 phases: structure and properties.

Tao LiuShi-Chang LiTao GaoBingyun Ao
Published in: RSC advances (2019)
Density functional theory (DFT) was used to predict and study protactinium pentoxide (Pa 2 O 5 ), which presents a fluorite and layered protactinium oxide-type structure. Although the layered structure has been observed with the isostructural transition Nb and Ta metal pentoxides experimentally, the detailed structure and properties of the layered Pa 2 O 5 are not clear and understandable. Our theoretical prediction explored some possible stable structures of the Pa 2 O 5 stoichiometry according to the existing M 2 O 5 structures (where M is an actinide Np or transition Nb, Ta, and V metal) and replacing the M ions with protactinium ions. The structural, mechanical, thermodynamic and electronic properties including lattice parameters, bulk moduli, elastic constants, entropy and band gaps were predicted for all the simulated structures. Pa 2 O 5 in the β-V 2 O 5 structure was found to be a competitive structure in terms of stability, whereas Pa 2 O 5 in the ζ-Nb 2 O 5 structure was found to be the most stable overall. This is consistent with Sellers's experimental observations. In particular, Pa 2 O 5 in the ζ-Nb 2 O 5 structure is predicted to be charge-transfer insulators. Furthermore, we predict that ζ-Nb 2 O 5 -structured Pa 2 O 5 is the most thermodynamically stable under ambient conditions and pressure.
Keyphrases
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