Next Article in Journal
Experimental and Numerical Studies on the Behaviors of Autoclaved Aerated Concrete Panels with Insulation Boards Subjected to Wind Loading
Previous Article in Journal
Analysis of the Physico-Chemical, Mechanical and Biological Properties of Crosslinked Type-I Collagen from Horse Tendon: Towards the Development of Ideal Scaffolding Material for Urethral Regeneration
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Materials
Volume 14
Issue 24
10.3390/ma14247650
materials-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Unconventional Stoichiometries of Na–O Compounds at High Pressures

by
Lihua Yang
1,2,
Yukai Zhang
1,
Yanli Chen
1,*,
Xin Zhong
1,
Dandan Wang
1,
Jihui Lang
1,
Xin Qu
1,* and
Jinghai Yang
1,*
1
Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, National Demonstration Center for Experimental Physics Education, College of Physics, Jilin Normal University, Siping 136000, China
2
State Key Laboratory of Integrated Optoelectronics, College of Materials Science and Engineering, Jilin University, Changchun 130012, China
*
Authors to whom correspondence should be addressed.
Materials 2021, 14(24), 7650; https://doi.org/10.3390/ma14247650
Submission received: 7 October 2021 / Revised: 4 December 2021 / Accepted: 10 December 2021 / Published: 12 December 2021
Browse Figures
Versions Notes

Abstract

:
It has been realized that the stoichiometries of compounds may change under high pressure, which is crucial in the discovery of novel materials. This work uses systematic structure exploration and first-principles calculations to consider the stability of different stoichiometries of Na–O compounds with respect to pressure and, thus, construct a high-pressure stability field and convex hull diagram. Four previously unknown stoichiometries (NaO5, NaO4, Na4O, and Na3O) are predicted to be thermodynamically stable. Four new phases (P2/m and Cmc21 NaO2 and Immm and C2/m NaO3) of known stoichiometries are also found. The O-rich stoichiometries show the remarkable features of all the O atoms existing as quasimolecular O2 units and being metallic. Calculations of the O–O bond lengths and Bader charges are used to explore the electronic properties and chemical bonding of the O-rich compounds. The Na-rich compounds stabilized at extreme pressures (P > 200 GPa) are electrides with strong interstitial electron localization. The C2/c phase of Na3O is found to be a zero-dimensional electride with an insulating character. The Cmca phase of Na4O is a one-dimensional metallic electride. These findings of new compounds with unusual chemistry might stimulate future experimental and theoretical investigations.

1. Introduction

Sodium and oxygen are among the most abundant elements in the solar system [1]. Sodium readily interacts with oxygen, typically producing Na2O, in which Na and O have oxidation states +1 and −2, respectively. Sodium can also react with oxygen to form sodium peroxide (Na2O2), sodium superoxide (NaO2), and sodium ozonide (NaO3), in which peroxide (O22−), superoxide (O2−), and ozonide (O3−) groups, respectively, act as anions [2]. Na–O compounds have broad applications, e.g., as oxidizing agents, oxygen sources, and magnetic materials [3,4]. They are also the discharge products of Na–air batteries [5,6,7]. Therefore, obtaining an in-depth understanding of the structure and properties of Na–O compounds under different external conditions is of fundamental importance. The high-pressure structures and properties of these Na–O compounds have been widely investigated both experimentally and theoretically at 50 GPa [5,8,9,10,11,12].
Pressure is a powerful tool to rearrange electrons, modify chemical bonding, and create new exotic materials [13,14,15,16,17,18]. The rapid development of structure prediction has facilitated the discovery of pressure-stabilized compounds with unusual stoichiometries; examples include S–H [19,20,21], Na–Cl [22], Xe–O/Fe [23,24], and La–H [25,26]. Some of them have subsequently been successfully synthesized [27,28]. Alkali metal sodium is a typical element showing an intriguing structure and properties under compression. For instance, the observed anomalous insulativity in the first high-pressure electride Na-hP4 [29] led to a research boom on high-pressure electrides. Similarly, many novel stoichiometries and chemical properties have been found in the Na–Cl system under high pressure [22]; Na3Cl, Na2Cl, Na3Cl2, NaCl3, and NaCl7 are theoretically stable and show unusual bonding and electronic properties. Remarkably, the most inert element, He, has shown the ability to form a compound, Na2He, at pressure greater than 113 GPa [30]. Oxygen also shows intriguing structures and oxidation states under compression. It is also the third most abundant element in the Earth′s crust; hence, understanding its behavior under extreme pressures provides important insights into planetary interiors and oxidation chemistry [2]. A recent experimental and theoretical study found an unconventional pressure-stabilized divalent ozonide CaO3 crystal with intriguing bonding; its existence has profound geological implications [31]. Recent discoveries of iron oxides with unusual oxidation states (FeO2 [32], Fe2O3 [33], and Fe5O6 [34]) are also notable.
Considering the intriguing stoichiometries, structures, and electronic properties of Na- and O-related substances under compression, binary compounds formed by Na and O atoms show relatively simple high-pressure behaviors. Thus, one might wonder whether new phenomenon (new stoichiometries, structures, and electronic properties) can be observed for Na–O systems at elevated pressures. Thus, this work reports a systematic search for crystal structures of different Na–O stoichiometries at pressures of 50–300 GPa with the aim of finding compounds unavailable under ambient conditions. Four new stoichiometries are predicted to be thermodynamically stable: NaO5, NaO4, Na4O, and Na3O. Four new phases (P2/m and Cmc21 NaO2 and Immm and C2/m NaO3) of known stoichiometries are also found. The O-rich stoichiometries show the remarkable feature of having all the O atoms existing as quasimolecular O2 units and being metallic. Calculations of the O–O bond lengths and Bader charges are used to explore the electronic properties and chemical bonding of the O-rich compounds. The Na-rich Na–O compounds stabilized at extreme pressures (P > 200 GPa) are electrides with strong interstitial electron localization. The C2/c phase of Na3O is found to be a zero-dimensional (0D) electride with an insulating character. The Cmca phase of Na4O is a one-dimensional (1D) metallic electride.

2. Computational Methods and Details

Structure searching for the Na–O system was performed using Crystal Structure Analysis by Particle Swarm Optimization (CALYPSO) [35,36,37], an established method that has successfully predicted high-pressure structures in many systems [38,39,40,41]. The underlying structural relaxations and electronic structure calculations were performed using the Vienna ab initio Simulation Package (VASP) [42] with the Perdew–Burke–Ernzerhof generalized gradient approximation functional [43]. We used the projector augmented wave (PAW) [44] method to describe the valence electrons of the Na (2s22p63s1) and O (2s22p4) atoms. We use a kinetic energy cutoff of 400 eV and k-point sampling with 0.3 Å−1 grid spacing. Each structure searching calculation generated 1200–1500 structures. After the structure searching, a kinetic energy cutoff of 1000 eV and dense k-point sampling with grid spacing of 0.1 Å−1 were used to ensure that enthalpy calculations were well converged to ~1 meV/atom. Phonon calculations with a supercell were performed using the PHONOPY code [45]. Electron localization functions (ELFs) were drawn using VESTA software [46], and Bader’s quantum theory was adopted to calculate charge transfer [47].

3. Results and Discussion

3.1. Stable Na–O Compounds at High Pressure

Our extensive searches for crystal structures of NaxOy (x = 1–4 and y = 1–5) considered pressures of 50, 100, 200, and 300 GPa with simulation cells having up to four formula units (f.u.) for each fixed composition using CALYPSO methodology, which allows efficiently finding stable structures given only the chemical composition [35,36,37]. All the candidate structures were relaxed using the VASP code [42], and thermodynamic stabilities were systematically investigated by calculating the formation enthalpies relative to Na and O at the corresponding pressure. The enthalpy of formation per atom is calculated as follows:
ΔH = [H(NaxOy) − xH(Na) − yH(O)]/(x + y)
Convex hull data at 0 K under different pressures (summarized in Figure 1a) show the stable compounds and phases as lying on the global stability line of the convex hull. The open symbols on the dotted lines represent unstable or metastable, and they decompose into other NaxOy compounds or elemental solid Na and O.
The calculated formation enthalpies of NaxOy compounds in Figure 1a show that already known compounds of Na2O, Na2O2, NaO2, and NaO3 lie on the convex hulls at the whole pressure range. NaO3 is known to possess an Im2m phase at ambient pressure [11]. Yang [5] reported NaO2 to have three stable high-pressure phases (Pnnm, Immm, and P4/mbm) between 0 and 50 GPa. It has been reported that Na2O2 is stable in Amm2 (distorted P 6 ¯ 2m) and P21/c phases at low temperature [8]. However, the P 6 ¯ 2m and Pbam structures become the most stable at elevated temperature under pressures up to 300 GPa [9]. Na2O undergoes phase transition from a cubic antifluorite (Fm 3 ¯ m) structure to an orthorhombic anticotunnite structure (Pnma), and then to a Ni2In-type (P63/mmc) structure [10].
At elevated pressures, four new phases (P2/m and Cmc21 NaO2, Immm and C2/m NaO3) of the compounds with known stoichiometry were found. Moreover, new stoichiometries NaO5, NaO4, Na4O, and Na3O became thermodynamically stable. An Immm phase of NaO5 stabilized at 50 GPa, and then transformed to a P-1 phase at 107.6 GPa. NaO4 stabilized in a P21/c phase above 66.8 GPa, and then transformed to a P-1 phase at 127 GPa. Na3O stabilized at 217 GPa in a C/2c structure, and Na4O stabilized at 205 GPa in a Cmca structure. To provide further information potentially useful for experimental synthesis, Figure 1b shows calculated pressure–composition diagrams of the stable Na–O compounds. All of the predicted compounds were dynamically stable without any imaginary phonon modes in the whole Brillouin zone (Figure S1 in the Supplementary Materials). Table S1 gives detailed structural information, and auxiliary POSCAR files are added below Table S1 in the Supplementary Materials.

3.2. O-Rich Compounds

The O-rich compounds showed a remarkable feature of having all O atoms as quasimolecular O2 units. In addition to the previously proposed structures, new structures and stoichiometries were found, as discussed below in detail. To analyze these new structures, we calculated the O–O bond lengths and Bader charges in established structures of C/2m O2 [52], Pbam Na2O2 [9], P4/mbm NaO2 [5], and P63/mmc Na2O [10] at pressures of 50–300 GPa for comparison (Table S2).
For NaO2, in addition to three previously proposed structures (Pnnm, Immn, and P4/mbm) [5], two new structures were found: P2/m (2 f.u./cell) and Cmc21 (4 f.u./cell). The former contained one Na atom at the 2 m position and two inequivalent O atoms at 2 m sites. The O–O distances were 1.22 and 1.28 Å at 200 GPa. Within this structure, each Na atom was coordinated with 10 O atoms, forming pentagonal prisms (Figure 2a). The calculated Bader charges were −0.71 for O1–O1 and −0.94 for O2–O2 quasimolecular O2 units, indicating that the oxidation state of the two quasimolecular O2 units in P2/m NaO2 was −1. These results confirm that this species can be viewed as a superoxide group O2–. Cmc21 NaO2 stabilized above 244 GPa and consisted of two inequivalent Na atoms at the 4a position and four inequivalent O atoms at the 4a sites (Figure 2b). Within the Cmc21 structure, Na1 and Na2 atoms were coordinated with 10 and eight O atoms, respectively. The O1–O2 distance was 1.16 Å, and the calculated Bader charges of −0.25 at 300 GPa imply an intermediate bonding situation. The O3–O4 distance was 1.34 Å, and the calculated Bader charges were −1.39 at 300 GPa, comparable to the 1.37 Å distance and −1.62 charge transfer in the peroxide (O22–) of Na2O2 at 300 GPa (Table S2). These results confirm that the O3–O4 quasimolecular O2 units can be viewed as O22– units, which were first observed in superoxide. This indicates that the superoxide group is not maintained in NaO2 with increasing pressure.
An Im2m phase of NaO3 containing unusual ozone anions at ambient pressure was previously reported [11]. Our calculations found two new NaO3 phases (Immm (2 f.u./cell) and C2/m (2 f.u./cell)) whose O atoms existed as quasimolecular O2 units rather than ozone anions. The Immm structure contained one Na atom at the 4e position and two inequivalent O atoms at the 8 m and 4f sites (Figure 2c). The Na was coordinated with 10 O atoms; O1 was coordinated with three Na atoms, whereas O2 was coordinated with two Na atoms and one O2 atom (Figure 2c). The O2–O2 bond length of 1.28 Å is close to the distance within the superoxide group (O2–) in NaO2 (1.31 Å) at 50 GPa. The calculated Bader charge of the O2–O2 quasimolecular O2 units was −0.67, comparable to that in NaO2 (−0.84; Table S2). These results confirm that O2–O2 quasimolecular O2 units can be viewed as O2– units with a −1 formal oxidation state. The O1–O1 distance in Immm NaO3 was 1.24 Å at 50 GPa, lying between that in neutral molecular oxygen (1.20 Å at 50 GPa) and the superoxide anion O2− (1.31 Å at 50 GPa). The calculated Bader charge of O1–O1 quasimolecular O2 units was −0.39. The calculated Bader charge and O1–O1 distance suggest that the O1–O1 quasimolecular O2 units had an intermediate bonding situation. In the C2/m NaO3 structure, the Na atom was coordinated with nine O atoms, and the O–O distances were 1.20 and 1.21 Å at 300 GPa (Figure 2d). The O–O distance and Bader charges (Table S1) suggest these quasimolecular O2 units had an intermediate bonding situation that did not coincide with that of any known O2 functional group.
NaO4 stabilized in a P21/c structure (4 f.u./cell) above 66.8 GPa. The structure had one Na atom at the 4e position and four inequivalent O atoms at the 4e sites. The O–O distances were 1.21 Å and 1.25 Å at 120 GPa. Each Na was surrounded by 11 O atoms, forming an irregular polyhedron (Figure 2e). At 127 GPa, the P21/c structure transitioned to P-1 NaO4 (2 f.u./cell) with O–O distances of 1.18 and 1.21 Å at 300 GPa (Figure 2f). The O–O distances and Bader charges (Table S1) indicate that all quasimolecular O2 units in P21/c and P-1 NaO4 phases had an intermediate bonding situation that did not coincide with that shown by any known O2 functional group. Previous studies of lithium oxides at high pressure [53,54] reported LiO4 phases with space groups of Ibam or I4/mcm at 50 GPa. The more accurate calculation used here for the Na–O system found the P21/c structure to be energetically favorable at 50 GPa.
Our calculations for NaO5, the most O-rich Na–O composition, found two crystal structures with Immm (2 f.u./cell) and P-1 (2 f.u./cell) symmetries. The Immm contained one Na atom at the 4i position and two inequivalent O atoms at the 16o and 4j sites (Figure 2g). The Na atom was coordinated with 10 O atoms, and each O atom was coordinated with two Na atoms and one O atom. The O–O distances (1.23 and 1.27 Å at 50 GPa) were intermediate between those in neutral molecular oxygen (1.20 Å at 50 GPa) and in the superoxide anion O2− (1.31 Å at 50 GPa). Compressing Immm NaO5 transformed it into P-1 NaO5 at 107.6 GPa. This structure had each Na atom coordinated with nine O atoms (Figure 2i). The O–O bond lengths (1.18 and 1.21 Å) were much shorter than those in the Immm structure. The calculated Bader charges and O–O distances indicate that NaO5 and NaO4 showed similar results, implying an intermediate bonding situation of all the oxygen pairs, which did not coincide with that shown by any known O2 functional group. Enhancing the O content in transition metal oxides can generally obtain O22− or O2− groups [55,56,57], whereas the high-oxygen-content Na–O compounds of the present study did not give these groups.
To understand the electronic structures of O-rich compounds, we calculated the projected density of states (PDOS). All the O-rich compounds shared similar features. Thus, we present the PDOS of the lower-pressure structures for each compound in Figure 3 as representatives and provide the PDOS of higher-pressure structures in Figure S2 in the Supplementary Materials. As can be seen form Figure 3, the O 2p states dominated the valance bands, while the contribution of Na to the valance states was negligible since electrons were transferred from Na to O. However, there were insufficient Na atoms to donate their electrons to fully occupy the O 2p states. All these O-rich compounds were electron-deficient, and the partially occupied O 2p electronic bands led to metallicity. All the metallic O-rich compounds were nonmagnetic, similar to YO3 [55], LiO2 [54], and NaO2 [5]. This can be attributed to pressure-induced magnetic collapse [58].

3.3. Na-Rich Compounds

Compression stabilized Na3O at 217 GPa with a C2/c structure and Na4O at 205 GPa with a Cmca structure. In the C2/c Na3O structure, the O atom was surrounded by 11 Na atoms, forming a 17-faced polyhedron. The distance between neighboring oxygen atoms was 2.65 Å at 300 GPa (Figure 4a). In Cmca Na4O, the coordination number of O increased to 12, and neighboring oxygen atoms were 2.73 Å apart at 300 GPa (Figure 4d). Both phases had all O atoms as oxide ions rather than quasimolecular O2 units. The Na-rich Na–O materials are naturally electron-rich systems, making them potential candidate electride materials. Electrides have some electrons localized at interstitial regions, rather than being attached to atoms, and these electrons behave as anions [59]. According to the dimensionality of the anionic electrons and corresponding interstitial spaces where the electrons are trapped, electrides can be classified into zero-dimensional (0D), one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) electrides [60]. Miao and Hoffmann attributed the formation of high-pressure electrides to external pressure inducing changes in energy between the interstitial space and the valence orbitals of atoms [15,61].
The calculated Bader charges for the C2/c Na3O and Cmca NaO4 phases show that charge was transferred from Na to both O and interstitial spaces (Table S1). The electrons provided by Na atoms were first captured by O atoms to reach a stable eight-electron closed-shell configuration. Further electrons from the Na were then trapped in the interstitial spaces, favoring electride formation. Subsequent ELF analysis characterized the localization of the excess electrons. The ELF maps for C2/c Na3O and Cmca Na4O with an isosurface value of 0.7 at 300 GPa (Figure 4b,e) clearly show electrons localized in the interstices of the crystal, suggesting electride formation. Anionic electrons in the C2/c Na3O electride were limited to 0D (Figure 4b). The anionic electrons in 0D electrides are completely localized in the void of the crystal and do not contribute to the conductivity of the system. Thus, 0D electrides tend to form semiconductors or insulators, such as the insulating phase of Na-hP4 [29] at 320 GPa and semiconductor phase of Li-aba2-40 [39] at 70 GP. The other structure, Cmca Na4O, was a 1D electride in which anionic electrons were delocalized in a channel, in which the electrons could move along the channel, leading to a metallic nature. The electronic properties of both structures were explored through PDOS calculations (Figure 4c,f). C2/c Na3O was clearly insulating due to Na–O ionic bonding and the localized 0D interstitial electrons. However, Cmca Na4O was metallic; the states around the Fermi level were all mainly contributed by the Na 3p and 3s orbitals and O 2p orbitals (Figure 4f). Similar electride suboxides, Li6O [54] and Mg3O2 [62], have also been reported at high pressure. Na4O is a non-superconducting metal electride.
To show the general trend of electronic properties of the Na–O compounds, we summarize the DOSs at the Fermi level for various Na–O compounds at 300 GPa as a function of Na content in Figure S3 in the Supplementary Materials. It can be seen that all the O-rich compounds were metallic due to their electron-deficient character as aforementioned. For the Na2O2 and Na2O compounds, the octet rule was achieved as the peroxide O22− group or O2− anions acquired exactly two electrons from the two Na atoms, leading to an insulating character. The Na-rich compounds, Na3O and Na4O, should be metallic due to the existence of excess electrons. However, the formation of the 0D electride made Na3O an insulator.

4. Conclusions

In summary, we used systematic structure exploration and first-principles calculations to construct a high-pressure stability field and convex hull diagram of the Na–O system with different stoichiometries at pressures of 50–300 GPa. Four previously unknown stoichiometries (NaO5, NaO4, Na4O, and Na3O) and four new phases of known stoichiometries (P2/m and Cmc21 NaO2 and Immm and C2/m NaO3) were predicted to be thermodynamically stable. Remarkably, the O-rich stoichiometries showed all O atoms to exist in quasimolecular O2 units in a metallic state. Calculated O–O bond lengths and Bader charges were used to explore the electronic properties and chemical bonding of the O-rich compounds. The Na-rich compounds stabilized at extreme pressures (P > 200 GPa) as electrides with strong interstitial electron localization. Electrons in C2/c Na3O localized to 0D, making the compound an insulator. In contrast, Cmca Na4O was revealed as a 1D electride with metallic features. This work provides guidance for further experimental studies of the properties of the Na–O system.

Supplementary Materials

The following are available online at https://www.mdpi.com/article/10.3390/ma14247650/s1: Figure S1. Phonon dispersion curves of the predicted Na–O compounds at the respective stable pressures; Figure S2. The PDOS of the predicted O-rich Na–O compounds; Figure S3. The DOS at the Fermi level versus sodium content of Na–O compounds at 300 GPa; Table S1. Structure details of the conventional unit cell of NaxOy from the CALYPSO structure searches at different pressures and auxiliary POSCAR files; Table S2. Calculated O–O bond lengths and Bader charges.

Author Contributions

Conceptualization, X.Q. and J.Y.; supervision, J.L., X.Z. and J.Y.; resources, L.Y. and J.L.; writing—original draft preparation, L.Y. and Y.Z.; writing—review and editing, Y.C., D.W., and J.L. All authors read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China, grant numbers 11904129 and 22078124, the Program for the Development of Science and Technology of Jilin Province, grant numbers 20190103040JH, 20190103039JH, YDZJ202101ZYTS065, 20190103043JH, and 20190103100JH, the Central Government Guided Local Science and Technology Development Fund for Basic Research of Jilin Province, grant number 202002015JC, the Scientific and Technological Research Project of the “13th Five-Year Plan” of Jilin Provincial Education Department, grant numbers JJKH20200408KJ and JJKH20200406KJ, and the Open Project of State Key Laboratory of Superhard Materials, Jilin University, grant numbers 201911 and 201908.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding authors.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Hubbard, W.B. Planetary Interiors; Van Nostrand Reinhold: New York, NY, USA, 1984. [Google Scholar]
  2. Vol’nov, I.I. Peroxides, Superoxides, and Ozonides of Alkali and Alkaline Earth Metals; Springer: Boston, MA, USA, 1966. [Google Scholar]
  3. Song, K.; Agyeman, D.A.; Park, M.; Yang, J.; Kang, Y.M. High-Energy-Density Metal–Oxygen Batteries: Lithium–Oxygen Batteries vs Sodium–Oxygen Batteries. Adv. Mater. 2017, 29, 1606572. [Google Scholar] [CrossRef] [PubMed]
  4. Hartmann, P.; Grübl, D.; Sommer, H.; Janek, J.; Bessler, W.G.; Adelhelm, P. Pressure Dynamics in Metal–Oxygen (Metal–Air) Batteries: A Case Study on Sodium Superoxide Cells. J. Phys. Chem. C 2014, 118, 1461–1471. [Google Scholar] [CrossRef]
  5. Deng, N.; Yang, G.; Wang, W.; Qiu, Y. Structural transitions and electronic properties of sodium superoxide at high pressures. RSC Adv. 2016, 6, 67910. [Google Scholar] [CrossRef]
  6. Yang, S.; Siegel, D.J. Intrinsic Conductivity in Sodium–Air Battery Discharge Phases: Sodium Superoxide vs Sodium Peroxide. Chem. Mater. 2015, 27, 3852–3860. [Google Scholar] [CrossRef]
  7. Zhang, W.; Zhao, C.; Wu, X. Research Progresses on Interfaces in Solid-State Sodium Batteries: A Topic Review. Adv. Mater. Interfaces 2020, 7, 2001444. [Google Scholar] [CrossRef]
  8. Jimlim, P.; Tsuppayakorn-aek, P. Theoretical predictions for low–temperature phases, softening of phonons and elastic stiffnesses, and electronic properties of sodium peroxide under high pressure. RSC Adv. 2019, 9, 30964–30975. [Google Scholar] [CrossRef] [Green Version]
  9. Deng, N.; Wang, W.; Yang, G.; Qiu, Y. Structural and electronic properties of alkali metal peroxides at high pressures. RSC Adv. 2015, 5, 104337–104342. [Google Scholar] [CrossRef]
  10. Čančarević, Ž.; Schön, J.C.; Jansen, M. Stability of alkali–metal oxides as a function of pressure: Theoretical calculations. Phys. Rev. B. 2006, 73, 224114. [Google Scholar] [CrossRef]
  11. Lein, W.K.; Armbruster, K.; Jansen, M. Synthesis and crystal structure determination of sodium ozonide. Chem. Commun. 1998, 6, 707–708. [Google Scholar]
  12. Carter, G.F.; Templeton, D.H. Polymorphism of Sodium Superoxide. J. Am. Chem. Soc. 1953, 75, 5247–5249. [Google Scholar] [CrossRef]
  13. Zhang, L.; Wang, Y.; Lv, J.; Ma, Y. Materials discovery at high pressures. Nat. Rev. Mater. 2017, 2, 17005. [Google Scholar] [CrossRef]
  14. Li, Y.; Hao, J.; Liu, H.; Li, Y.; Ma, Y. The metallization and superconductivity of dense hydrogen sulfifide. J. Chem. Phys. 2014, 140, 174712. [Google Scholar] [CrossRef] [Green Version]
  15. Miao, M.-S.; Hoffmann, R. High–pressure electrides: The chemical nature of interstitial quasiatoms. J. Am. Chem. Soc. 2015, 137, 3631–3637. [Google Scholar] [CrossRef] [PubMed]
  16. Pepin, C.M.; Geneste, G.; Dewaele, A.; Mezouar, M.; Loubeyre, P. Synthesis of FeH5: A layered structure with atomic hydrogen slabs. Science 2017, 357, 382. [Google Scholar] [CrossRef] [Green Version]
  17. Yang, G.; Wang, Y.; Peng, F.; Bergara, A.; Ma, Y. Gold as a 6p–element in dense lithium aurides. J. Am. Chem. Soc. 2016, 138, 4046–4052. [Google Scholar] [CrossRef]
  18. Zhao, Z.; Zhang, S.; Yu, T.; Xu, H.; Bergara, A.; Yang, G. Predicted pressure–induced superconducting transition in electride Li6P. Phys. Rev. Lett. 2019, 122, 097002. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  19. Duan, D.; Liu, Y.; Tian, F.; Li, D.; Huang, X.; Zhao, Z.; Yu, H.; Liu, B.; Tian, W.; Cui, T. Pressure–induced metallization of dense (H2S)2 H2 with high–Tc superconductivity. Sci. Rep. 2014, 4, 6968. [Google Scholar] [CrossRef] [Green Version]
  20. Gao, G.; Wang, L.; Li, M.; Zhang, J.; Howie, R.T.; Gregoryanz, E.; Struzhkin, V.V.; Wang, L.; Tse, J.S. Superconducting binary hydrides: Theoretical predictions and experimental progresses. Mater. Today Phys. 2021, 21, 100546. [Google Scholar] [CrossRef]
  21. Einaga, M.; Sakata, M.; Ishikawa, T.; Shimizu, K.; Eremets, M.I.; Drozdov, A.P.; Troyan, I.A.; Hirao, N.; Ohishi, Y. Crystal structure of the superconducting phase of sulfur hydride. Nat. Phys. 2016, 12, 835–838. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  22. Zhang, W.; Oganov, A.R.; Goncharov, A.F.; Zhu, Q.; Boulfelfel, S.E.; Lyakhov, A.O.; Stavrou, E.; Somayazulu, M.; Prakapenka, V.B.; Konôpková, Z. Unexpected stable stoichiometries of sodium chlorides. Science 2013, 342, 1502. [Google Scholar] [CrossRef] [Green Version]
  23. Zhu, L.; Liu, H.; Pickard, C.J.; Zou, G.; Ma, Y. Reactions of xenon with iron and nickel are predicted in the Earth’s inner core. Nat. Chem. 2014, 6, 644. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  24. Dewaele, A.; Worth, N.; Pickard, C.J.; Needs, N.W.R.J.; Pascarelli, S.; Mathon, O.; Mezouar, S.P.O.M.M.; Irifune, T. Synthesis and stability of xenon oxides Xe2O5 and Xe3O2 under pressure. Nat. Chem. 2016, 8, 784. [Google Scholar] [CrossRef] [Green Version]
  25. Peng, F.; Sun, Y.; Pickard, C.J.; Needs, R.J.; Wu, Q.; Ma, Y. Hydrogen clathrate structures in rare earth hydrides at high pressures: Possible route to room–temperature superconductivity. Phys. Rev. Lett. 2017, 119, 1. [Google Scholar] [CrossRef]
  26. Liu, H.; Naumov, I.I.; Hoffmann, R.; Ashcroft, N.W.; Hemley, R.J. Potential high-Tc superconducting lanthanum and yttrium hydrides at high pressures. Proc. Natl. Acad. Sci. USA 2017, 114, 6990. [Google Scholar] [CrossRef] [Green Version]
  27. Somayazulu, M.; Ahart, M.; Mishra, A.K.; Geballe, Z.M.; Baldini, M.; Meng, Y.; Struzhkin, V.V.; Hemley, R.J. Evidence for superconductivity above 260 K in Lanthanum superhydride at megabar pressures. Phys. Rev. Lett. 2019, 122, 27001. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  28. Drozdov, A.P.; Eremets, M.I.; Troyan, I.A.; Ksenofontov, V.; Shylin, S.I. Conventional superconductivity at 203 kelvin at high pressures in the sulfur hydride system. Nature 2015, 525, 73–76. [Google Scholar] [CrossRef]
  29. Ma, Y.; Eremets, M.; Oganov, A.R.; Xie, Y.; Trojan, I.; Medvedev, S.; Lyakhov, A.O.; Valle, M.; Prakapenka, V. Transparent dense sodium. Nature 2009, 458, 182–185. [Google Scholar] [CrossRef]
  30. Dong, X.; Oganov, A.R.; Goncharov, A.F.; Stavrou, E.; Lobanov, S.; Saleh, G.; Qian, G.-R.; Zhu, Q.; Gatti, C.; Deringer, V.L.; et al. A stable compound of helium and sodium at high pressure. Nat. Chem. 2017, 9, 440–445. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  31. Wang, Y.; Xu, M.; Yang, L.; Yan, B.; Qin, Q.; Shao, X.; Zhang, Y.; Huang, D.; Lin, X.; Lv, J.; et al. Pressure–stabilized divalent ozonide CaO3 and its impact on Earth’s oxygen cycles. Nat. Commun. 2020, 11, 4702. [Google Scholar] [CrossRef] [PubMed]
  32. Hu, Q.; Kim, D.Y.; Yang, W.; Yang, L.; Meng, Y.; Zhang, L.; Mao, H. FeO2 and FeOOH under deep lower–mantle conditions and Earth’s oxygen–hydrogen cycles. Nature 2016, 534, 241. [Google Scholar] [CrossRef]
  33. Bykova, E.; Dubrovinsky, L.; Dubrovinskaia, N.; Bykov, E.B.N.D.M.; McCammon, C.; Ovsyannikov, S.V.; Liermann, H.-P.; Kupenko, I.; Chumakov, A.I.; Rüffer, R.; et al. Structural complexity of simple Fe2O3 at high pressures and temperatures. Nat. Commun. 2016, 7, 10661. [Google Scholar] [CrossRef] [PubMed]
  34. Lavina, B.; Meng, Y. Unraveling the complexity of iron oxides at high pressure and temperature: Synthesis of Fe5O6. Sci. Adv. 2015, 1, e1400260. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  35. Wang, Y.; Lv, J.; Ma, Y.; Cui, T.; Zou, G. Superconductivity of MgB2 under Ultra high Pressure: A First–Principles Study. Phys. Rev. B 2009, 80, 092505. [Google Scholar] [CrossRef]
  36. Wang, Y.; Lv, J.; Zhu, L.; Ma, Y. CALYPSO: A Method for Crystal Structure Prediction. Comput. Phys. Commun. 2012, 183, 2063–2070. [Google Scholar] [CrossRef] [Green Version]
  37. Lv, J.; Wang, Y.; Zhu, L.; Ma, Y. Particle–swarm structure prediction on clusters. J. Chem. Phys. 2012, 137, 084104. [Google Scholar] [CrossRef]
  38. Zhu, L.; Wang, H.; Wang, Y.; Lv, J.; Ma, Y.; Cui, Q.; Ma, Y.; Zou, G. Substitutional Alloy of Bi and Te at High Pressure. Phys. Rev. Lett. 2011, 106, 18–21. [Google Scholar] [CrossRef]
  39. Lv, J.; Wang, Y.; Zhu, L.; Ma, Y. Predicted Novel High–Pressure Phases of Lithium. Phys. Rev. Lett. 2011, 106, 015503. [Google Scholar] [CrossRef]
  40. Li, Y.; Wang, L.; Liu, H.; Zhang, Y.; Hao, J.; Pickard, C.J.; Nelson, J.R.; Needs, R.J.; Li, W.; Huang, Y.; et al. Dissociation Products and Structures of Solid H2S at Strong Compression. Phys. Rev. B 2016, 93, 020103. [Google Scholar] [CrossRef] [Green Version]
  41. Zhang, J.; Lv, J.; Li, H.; Feng, X.; Lu, C.; Redfern, S.A.T.; Liu, H.; Chen, C.; Ma, Y. Rare Helium–Bearing Compound FeO2He Stabilized at Deep–Earth Conditions. Phys. Rev. Lett. 2018, 121, 255703. [Google Scholar] [CrossRef] [Green Version]
  42. Kresse, G.; Furthmuller, J. Efficient Iterative Schemes for Ab Initio Total–Energy Calculations Using a Plane–Wave Basis Set. Phys. Rev. B 1996, 54, 11169–11186. [Google Scholar] [CrossRef]
  43. Perdew, J.P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865–3868. [Google Scholar] [CrossRef] [Green Version]
  44. Blochl, P.E. Projector Augmented–Wave Method. Phys. Rev. B 1994, 50, 17953–17979. [Google Scholar] [CrossRef] [Green Version]
  45. Togo, A.; Oba, F.; Tanaka, I. First–Principles Calculations of the Ferroelastic Transition between Rutile–Type and CaCl2–Type SiO2. Phys. Rev. B 2008, 78, 134106. [Google Scholar] [CrossRef] [Green Version]
  46. Momma, K.; Izumi, F. VESTA 3 for Three–Dimensional Visualization of Crystal. Volumetric and Morphology Data. J. Appl. Crystallogr. 2011, 44, 1272–1276. [Google Scholar] [CrossRef]
  47. Bader, R.F.W. Atoms in Molecules. Acc. Chem. Res. 1985, 18, 9–15. [Google Scholar] [CrossRef]
  48. Ma, Y.; Oganov, A.R.; Xie, Y. High–Pressure Structures of Lithium, Potassium, Rubidium Predicted by an Ab Initio Evolutionary Algorithm. Phys. Rev. B 2008, 78, 014102. [Google Scholar] [CrossRef] [Green Version]
  49. Gregoryanz, E.; Lundegaard, L.F.; McMahon, M.I.; Guillaume, C.; Nelmes, R.J.; Mezouar, M. Structural Diversity of Sodium. Science 2008, 320, 1054–1057. [Google Scholar] [CrossRef]
  50. Hanfland, M.; Loa, I.; Syassen, K. Sodium under Pressure: Bcc to Fcc Structural Transition and Pressure–Volume Relation to 100 GPa. Phys. Rev. B 2002, 65, 184109. [Google Scholar] [CrossRef]
  51. Ackland, G.J.; Macleod, I.R. Origin of the Complex Crystal Structures of Elements at Intermediate Pressure. New J. Phys. 2004, 6, 138. [Google Scholar] [CrossRef]
  52. Ma, Y.; Oganov, A.R.; Glass, C.W. Structure of the metallic ζ–phase of oxygen and isosymmetric nature of the ε−ζ phase transition: Ab initio simulation. Phys. Rev. B 2007, 76, 64101. [Google Scholar] [CrossRef] [Green Version]
  53. Yang, W.; Kim, D.Y.; Yang, L.; Li, N.; Tang, L.; Amine, K.; Mao, H. Oxygen–Rich Lithium Oxide Phases Formed at High Pressure for Potential Lithium–Air Battery Electrode. Adv. Sci. 2017, 4, 1600453. [Google Scholar] [CrossRef] [Green Version]
  54. Dong, X.; Hou, J.; Kong, J.; Cui, H.; Li, Y.; Oganov, A.R.; Li, K.; Zheng, H.; Zhou, X.; Wang, H.-T. Predicted lithium oxide compounds and superconducting low–pressure LiO4. Phys. Rev. B 2019, 100, 144104. [Google Scholar] [CrossRef] [Green Version]
  55. Yang, Q.; Lin, J.; Li, F.; Zhang, J.; Zurek, E.; Yang, G. Pressure–induced yttrium oxides with unconventional stoichiometries and novel properties. Phys. Rev. Mater. 2021, 5, 044802. [Google Scholar] [CrossRef]
  56. Zhang, J.; Oganov, A.R.; Li, X.; Esfahani, M.M.D.; Dong, H. First–principles investigation of Zr–O compounds, their crystal structures, and mechanical properties. J. Appl. Phys. 2017, 121, 155104. [Google Scholar] [CrossRef] [Green Version]
  57. Bouibes, A.; Zaoui, A. Investigating new polyphorms of Zn–O from variable composition. Solid State. Commun. 2015, 220, 36–38. [Google Scholar] [CrossRef]
  58. Maple, M.B.; Wittig, J.; Kim, K.S. Pressure-Induced Magnetic-Nonmagnetic Transition of Ce Impurities in La. Phys. Rev. Lett. 1969, 23, 1375. [Google Scholar] [CrossRef]
  59. Hosono, H.; Mishima, Y.; Takezoe, H.; MacKenzie, K.J.D. Nanomaterials: Research Towards Applications; Elsevier Science: Amsterdam, The Netherlands, 2006. [Google Scholar]
  60. Tsuji, Y.; Dasari, P.L.V.K.; Elatresh, S.F.; Hoffmann, R.; Ashcroft, N.W. Structural Diversity and Electron Confinement in Li4N; the Potential for 0-D, 2-D and 3-D Electrides. J. Am. Chem. Soc. 2016, 138, 14108. [Google Scholar] [CrossRef]
  61. Miao, M.-S.; Hoffmann, R. High Pressure Electrides: A Predictive Chemical and Physical Theory. Acc. Chem. Res. 2014, 47, 1311–1317. [Google Scholar] [CrossRef]
  62. Zhu, Q.; Oganov, A.R.; Lyakhov, A.O. Novel stable compounds in the Mg–O system under high pressure. Phys. Chem. Chem. Phys. 2013, 15, 7696. [Google Scholar] [CrossRef]
Materials 14 07650 g001 550
Figure 1. (a) Calculated formation enthalpy (ΔH) for each NaxOy composition relative to O and Na at 0 K. Solid symbols represent stable compounds, and open symbols represent metastable compounds. (b) Pressure range and structure of each stable compound. Na adopted the following structures: Na−bcc, Na−fcc, Na−cI16, Na−oP8, and Na−hP4 [29,48,49,50,51], and O adopted ζ phases with C2/m symmetry [52].
Figure 1. (a) Calculated formation enthalpy (ΔH) for each NaxOy composition relative to O and Na at 0 K. Solid symbols represent stable compounds, and open symbols represent metastable compounds. (b) Pressure range and structure of each stable compound. Na adopted the following structures: Na−bcc, Na−fcc, Na−cI16, Na−oP8, and Na−hP4 [29,48,49,50,51], and O adopted ζ phases with C2/m symmetry [52].
Materials 14 07650 g001
Materials 14 07650 g002 550
Figure 2. Crystal structures of the predicted O-rich Na–O compounds: (a) P2/m NaO2 at 200 GPa; (b) Cmc21 NaO2 at 300 GPa; (c) Immm NaO3 at 50 GPa; (d) C2/m NaO3 at 300 GPa; (e) P21/c NaO4 at 120 GPa; (f) P-1 NaO4 at 300 GPa; (g) Immm NaO5 at 50 GPa; (h) P-1 NaO5 at 300 GPa. Small spheres (dark and light red) represent O atoms; yellow spheres denote Na atoms.
Figure 2. Crystal structures of the predicted O-rich Na–O compounds: (a) P2/m NaO2 at 200 GPa; (b) Cmc21 NaO2 at 300 GPa; (c) Immm NaO3 at 50 GPa; (d) C2/m NaO3 at 300 GPa; (e) P21/c NaO4 at 120 GPa; (f) P-1 NaO4 at 300 GPa; (g) Immm NaO5 at 50 GPa; (h) P-1 NaO5 at 300 GPa. Small spheres (dark and light red) represent O atoms; yellow spheres denote Na atoms.
Materials 14 07650 g002
Materials 14 07650 g003 550
Figure 3. PDOS of the predicted O−rich Na−O compounds: (a) P2/m NaO2 at 200 GPa; (b) Immm NaO3 at 50 GPa; (c) P21/c NaO4 at 120 GPa; (d) Immm NaO5 at 50 GPa. The PDOS of Na is not shown, as it had negligible contributions near the Fermi energy. The Fermi energy (EF) was set to zero.
Figure 3. PDOS of the predicted O−rich Na−O compounds: (a) P2/m NaO2 at 200 GPa; (b) Immm NaO3 at 50 GPa; (c) P21/c NaO4 at 120 GPa; (d) Immm NaO5 at 50 GPa. The PDOS of Na is not shown, as it had negligible contributions near the Fermi energy. The Fermi energy (EF) was set to zero.
Materials 14 07650 g003
Materials 14 07650 g004 550
Figure 4. (a,d) Crystal structures, (b,e) ELF, and (c,f) PDOS of predicted Na-rich Na–O compounds at 300 GPa: (a–c) C2/c Na3O and (d–f) Cmca Na4O. O atoms are represented by bright red spheres; yellow spheres denote Na atoms. The interstitial electron regions are marked with blue arrows and dashed lines.
Figure 4. (a,d) Crystal structures, (b,e) ELF, and (c,f) PDOS of predicted Na-rich Na–O compounds at 300 GPa: (a–c) C2/c Na3O and (d–f) Cmca Na4O. O atoms are represented by bright red spheres; yellow spheres denote Na atoms. The interstitial electron regions are marked with blue arrows and dashed lines.
Materials 14 07650 g004
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Yang, L.; Zhang, Y.; Chen, Y.; Zhong, X.; Wang, D.; Lang, J.; Qu, X.; Yang, J. Unconventional Stoichiometries of Na–O Compounds at High Pressures. Materials 2021, 14, 7650. https://doi.org/10.3390/ma14247650

AMA Style

Yang L, Zhang Y, Chen Y, Zhong X, Wang D, Lang J, Qu X, Yang J. Unconventional Stoichiometries of Na–O Compounds at High Pressures. Materials. 2021; 14(24):7650. https://doi.org/10.3390/ma14247650

Chicago/Turabian Style

Yang, Lihua, Yukai Zhang, Yanli Chen, Xin Zhong, Dandan Wang, Jihui Lang, Xin Qu, and Jinghai Yang. 2021. "Unconventional Stoichiometries of Na–O Compounds at High Pressures" Materials 14, no. 24: 7650. https://doi.org/10.3390/ma14247650

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop