Understanding the Polymorphism of A4[(UO2)3(PO4 )2O2] (A = Alkali Metals) Uranyl Phosphate Framework Structures
Abstract
In this study we combine experimental synthesis and density functional theory (DFT) calculations to gain insight into the polymorphism of A4[(UO2)3(PO4)2O2] (A = Na, K, Rb, Cs) uranyl phosphate structures. Single crystals of a new 3D uranyl phosphate, Cs4[(UO2)3(PO4)2O2], were grown by molten flux methods using a CsCl flux. DFT calculations, using the DFT+U method, were carried out to study the difference between this new 3D uranyl phosphate and a family of recently described layered uranyl phosphates. Variation of the computed properties with changes in Ueff values are also studied. The DFT results agree with the experimental observations, showing that the Cs-containing 3D polymorph and the K-containing layered polymorphs are more stable than their respective layered and 3D polymorph. We show an increase in the difference between the total energies of the layered and 3D polymorphs and an increase in the band gaps with increasing $$U_{eff}$$ value. Volume-based thermodynamics was also applied to calculate the total energies of the different polymorphs, showing consistently higher stability of the layered polymorphs compared to the 3D polymorphs. For each of the studied polymorphs, we calculated the electronic, optical, and bonding properties. We also show an anisotropy in the absorption indexes along the three crystallographic directions of the polymorphs, which is especially noticeable in the layered polymorphs. We attribute the difference in the density of states to the different coordination of the U atoms in the layered and 3D polymorphs. We attribute the preferred formation of the 3D Cs polymorph to the substantial increase in the U–A bond strength, which is more pronounced than the differences in the bond strength between structures for other atomic pairs.
- Authors:
-
[1];
[1];
- Univ. of South Carolina, Columbia, SC (United States). Center for Hierarchical Wasteform Materials (CHWM), Nuclear Engineering Program
- Univ. of South Carolina, Columbia, SC (United States). Center for Hierarchical Wasteform Materials (CHWM), Department of Chemistry and Biochemistry
- Publication Date:
- Research Org.:
- Energy Frontier Research Centers (EFRC) (United States). Center for Hierarchical Waste Form Materials (CHWM); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC); Univ. of Miami, FL (United States)
- Sponsoring Org.:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- OSTI Identifier:
- 1543604
- Grant/Contract Number:
- SC0016575
- Resource Type:
- Accepted Manuscript
- Journal Name:
- Crystal Growth and Design
- Additional Journal Information:
- Journal Volume: 19; Journal Issue: 2; Journal ID: ISSN 1528-7483
- Publisher:
- American Chemical Society
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 36 MATERIALS SCIENCE; Chemistry; Crystallography; Materials Science
Citation Formats
Kocevski, Vancho, Juillerat, Christian A., Moore, Emily E., zur Loye, Hans-Conrad, and Besmann, Theodore M. Understanding the Polymorphism of A4[(UO2)3(PO4 )2O2] (A = Alkali Metals) Uranyl Phosphate Framework Structures. United States: N. p., 2018.
Web. doi:10.1021/acs.cgd.8b01518.
Kocevski, Vancho, Juillerat, Christian A., Moore, Emily E., zur Loye, Hans-Conrad, & Besmann, Theodore M. Understanding the Polymorphism of A4[(UO2)3(PO4 )2O2] (A = Alkali Metals) Uranyl Phosphate Framework Structures. United States. https://doi.org/10.1021/acs.cgd.8b01518
Kocevski, Vancho, Juillerat, Christian A., Moore, Emily E., zur Loye, Hans-Conrad, and Besmann, Theodore M. Thu .
"Understanding the Polymorphism of A4[(UO2)3(PO4 )2O2] (A = Alkali Metals) Uranyl Phosphate Framework Structures". United States. https://doi.org/10.1021/acs.cgd.8b01518. https://www.osti.gov/servlets/purl/1543604.
@article{osti_1543604,
title = {Understanding the Polymorphism of A4[(UO2)3(PO4 )2O2] (A = Alkali Metals) Uranyl Phosphate Framework Structures},
author = {Kocevski, Vancho and Juillerat, Christian A. and Moore, Emily E. and zur Loye, Hans-Conrad and Besmann, Theodore M.},
abstractNote = {In this study we combine experimental synthesis and density functional theory (DFT) calculations to gain insight into the polymorphism of A4[(UO2)3(PO4)2O2] (A = Na, K, Rb, Cs) uranyl phosphate structures. Single crystals of a new 3D uranyl phosphate, Cs4[(UO2)3(PO4)2O2], were grown by molten flux methods using a CsCl flux. DFT calculations, using the DFT+U method, were carried out to study the difference between this new 3D uranyl phosphate and a family of recently described layered uranyl phosphates. Variation of the computed properties with changes in Ueff values are also studied. The DFT results agree with the experimental observations, showing that the Cs-containing 3D polymorph and the K-containing layered polymorphs are more stable than their respective layered and 3D polymorph. We show an increase in the difference between the total energies of the layered and 3D polymorphs and an increase in the band gaps with increasing $U_{eff}$ value. Volume-based thermodynamics was also applied to calculate the total energies of the different polymorphs, showing consistently higher stability of the layered polymorphs compared to the 3D polymorphs. For each of the studied polymorphs, we calculated the electronic, optical, and bonding properties. We also show an anisotropy in the absorption indexes along the three crystallographic directions of the polymorphs, which is especially noticeable in the layered polymorphs. We attribute the difference in the density of states to the different coordination of the U atoms in the layered and 3D polymorphs. We attribute the preferred formation of the 3D Cs polymorph to the substantial increase in the U–A bond strength, which is more pronounced than the differences in the bond strength between structures for other atomic pairs.},
doi = {10.1021/acs.cgd.8b01518},
journal = {Crystal Growth and Design},
number = 2,
volume = 19,
place = {United States},
year = {Thu Dec 13 00:00:00 EST 2018},
month = {Thu Dec 13 00:00:00 EST 2018}
}
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