Structure and Properties of Some Layered U2O5 Phases: A Density Functional Theory Study

Marco Molinari, Nicholas A. Brincat, Geoffrey C. Allen, Stephen C. Parker

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

U2O5 is the boundary composition between the fluorite and the layered structures of the UO2→3 system and the least studied oxide in the group. δ-U2O5 is the only layered structure proposed so far experimentally, although evidence of fluorite-based phases has also been reported. Our DFT work explores possible structures of U2O5 stoichiometry by starting from existing M2O5 structures (where M is an actinide or transition metal) and replacing the M ions with uranium ions. For all structures, we predicted structural and electronic properties including bulk moduli and band gaps. The majority of structures were found to be less stable than δ-U2O5. U2O5 in the R-Nb2O5 structure was found to be a competitive structure in terms of stability, whereas U2O5 in the Np2O5 structure was found to be the most stable overall. Indeed, by including the vibrational contribution to the free energy using the frequencies obtained from the optimized unit cells we predict that Np2O5 structured U2O5 is the most thermodynamically stable under ambient conditions. δ-U2O5 only becomes more stable at high temperatures and/or pressures. This suggests that a low-temperature synthesis route should be tested and so potentially opens a new avenue of research for pentavalent uranium oxides.

LanguageEnglish
Pages4468-4473
Number of pages6
JournalInorganic Chemistry
Volume56
Issue number8
DOIs
Publication statusPublished - 5 Apr 2017

Fingerprint

Fluorspar
fluorite
Density functional theory
Actinoid Series Elements
Ions
uranium oxides
density functional theory
Uranium
bulk modulus
Discrete Fourier transforms
Stoichiometry
Electronic properties
Oxides
Free energy
uranium
Transition metals
Structural properties
stoichiometry
ions
Energy gap

Cite this

Molinari, Marco ; Brincat, Nicholas A. ; Allen, Geoffrey C. ; Parker, Stephen C. / Structure and Properties of Some Layered U2O5 Phases : A Density Functional Theory Study. In: Inorganic Chemistry. 2017 ; Vol. 56, No. 8. pp. 4468-4473.
@article{30179278f67146919b77464c8927e947,
title = "Structure and Properties of Some Layered U2O5 Phases: A Density Functional Theory Study",
abstract = "U2O5 is the boundary composition between the fluorite and the layered structures of the UO2→3 system and the least studied oxide in the group. δ-U2O5 is the only layered structure proposed so far experimentally, although evidence of fluorite-based phases has also been reported. Our DFT work explores possible structures of U2O5 stoichiometry by starting from existing M2O5 structures (where M is an actinide or transition metal) and replacing the M ions with uranium ions. For all structures, we predicted structural and electronic properties including bulk moduli and band gaps. The majority of structures were found to be less stable than δ-U2O5. U2O5 in the R-Nb2O5 structure was found to be a competitive structure in terms of stability, whereas U2O5 in the Np2O5 structure was found to be the most stable overall. Indeed, by including the vibrational contribution to the free energy using the frequencies obtained from the optimized unit cells we predict that Np2O5 structured U2O5 is the most thermodynamically stable under ambient conditions. δ-U2O5 only becomes more stable at high temperatures and/or pressures. This suggests that a low-temperature synthesis route should be tested and so potentially opens a new avenue of research for pentavalent uranium oxides.",
author = "Marco Molinari and Brincat, {Nicholas A.} and Allen, {Geoffrey C.} and Parker, {Stephen C.}",
year = "2017",
month = "4",
day = "5",
doi = "10.1021/acs.inorgchem.7b00014",
language = "English",
volume = "56",
pages = "4468--4473",
journal = "Inorganic Chemistry",
issn = "0020-1669",
publisher = "American Chemical Society",
number = "8",

}

Structure and Properties of Some Layered U2O5 Phases : A Density Functional Theory Study. / Molinari, Marco; Brincat, Nicholas A.; Allen, Geoffrey C.; Parker, Stephen C.

In: Inorganic Chemistry, Vol. 56, No. 8, 05.04.2017, p. 4468-4473.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Structure and Properties of Some Layered U2O5 Phases

T2 - Inorganic Chemistry

AU - Molinari, Marco

AU - Brincat, Nicholas A.

AU - Allen, Geoffrey C.

AU - Parker, Stephen C.

PY - 2017/4/5

Y1 - 2017/4/5

N2 - U2O5 is the boundary composition between the fluorite and the layered structures of the UO2→3 system and the least studied oxide in the group. δ-U2O5 is the only layered structure proposed so far experimentally, although evidence of fluorite-based phases has also been reported. Our DFT work explores possible structures of U2O5 stoichiometry by starting from existing M2O5 structures (where M is an actinide or transition metal) and replacing the M ions with uranium ions. For all structures, we predicted structural and electronic properties including bulk moduli and band gaps. The majority of structures were found to be less stable than δ-U2O5. U2O5 in the R-Nb2O5 structure was found to be a competitive structure in terms of stability, whereas U2O5 in the Np2O5 structure was found to be the most stable overall. Indeed, by including the vibrational contribution to the free energy using the frequencies obtained from the optimized unit cells we predict that Np2O5 structured U2O5 is the most thermodynamically stable under ambient conditions. δ-U2O5 only becomes more stable at high temperatures and/or pressures. This suggests that a low-temperature synthesis route should be tested and so potentially opens a new avenue of research for pentavalent uranium oxides.

AB - U2O5 is the boundary composition between the fluorite and the layered structures of the UO2→3 system and the least studied oxide in the group. δ-U2O5 is the only layered structure proposed so far experimentally, although evidence of fluorite-based phases has also been reported. Our DFT work explores possible structures of U2O5 stoichiometry by starting from existing M2O5 structures (where M is an actinide or transition metal) and replacing the M ions with uranium ions. For all structures, we predicted structural and electronic properties including bulk moduli and band gaps. The majority of structures were found to be less stable than δ-U2O5. U2O5 in the R-Nb2O5 structure was found to be a competitive structure in terms of stability, whereas U2O5 in the Np2O5 structure was found to be the most stable overall. Indeed, by including the vibrational contribution to the free energy using the frequencies obtained from the optimized unit cells we predict that Np2O5 structured U2O5 is the most thermodynamically stable under ambient conditions. δ-U2O5 only becomes more stable at high temperatures and/or pressures. This suggests that a low-temperature synthesis route should be tested and so potentially opens a new avenue of research for pentavalent uranium oxides.

UR - http://www.scopus.com/inward/record.url?scp=85018518343&partnerID=8YFLogxK

U2 - 10.1021/acs.inorgchem.7b00014

DO - 10.1021/acs.inorgchem.7b00014

M3 - Article

VL - 56

SP - 4468

EP - 4473

JO - Inorganic Chemistry

JF - Inorganic Chemistry

SN - 0020-1669

IS - 8

ER -