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Mazzola, F.; Hassani, H.; Amoroso, D.; Chaluvadi, S.K.; Fujii, J.; Polewczyk, V.; Rajak, P.; Koegler, M.; Ciancio, R.; Partoens, B.; Rossi, G.; Vobornik, I.; Ghosez, P.; Orgiani, P. |
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Title |
Unveiling the electronic structure of pseudotetragonal WO₃ thin films |
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A1 Journal article |
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Year  |
2023 |
Publication |
The journal of physical chemistry letters |
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14 |
Issue |
32 |
Pages |
7208-7214 |
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Keywords |
A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT) |
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Abstract |
WO3 isa 5d compound that undergoes severalstructuraltransitions in its bulk form. Its versatility is well-documented,with a wide range of applications, such as flexopiezoelectricity,electrochromism, gating-induced phase transitions, and its abilityto improve the performance of Li-based batteries. The synthesis ofWO(3) thin films holds promise in stabilizing electronicphases for practical applications. However, despite its potential,the electronic structure of this material remains experimentally unexplored.Furthermore, its thermal instability limits its use in certain technologicaldevices. Here, we employ tensile strain to stabilize WO3 thin films, which we call the pseudotetragonal phase, and investigateits electronic structure using a combination of photoelectron spectroscopyand density functional theory calculations. This study reveals theFermiology of the system, notably identifying significant energy splittingsbetween different orbital manifolds arising from atomic distortions.These splittings, along with the system's thermal stability,offer a potential avenue for controlling inter- and intraband scatteringfor electronic applications. |
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001044522400001 |
Publication Date |
2023-08-08 |
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1948-7185 |
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Additional Links |
UA library record; WoS full record |
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Impact Factor |
5.7 |
Times cited |
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Open Access |
OpenAccess |
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Most recent IF: 5.7; 2023 IF: 9.353 |
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Call Number |
UA @ admin @ c:irua:198391 |
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8951 |
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Author |
Hassani, H. |
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Title |
First-principles study of polarons in WO₃ |
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Doctoral thesis |
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Year |
2023 |
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Pages |
181 p. |
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Doctoral thesis; Condensed Matter Theory (CMT) |
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Polarons are quasiparticles emerging in materials from the interaction of extra charge carriers with the surrounding atomic lattice. They appear in a wide va- riety of compounds and can have a profound impact on their properties, making the concept of a polaron a central and ubiquitous topic in material science. Al- though the concept is known for about 75 years, the origin of polarons is not yet fully elucidated. This thesis focuses on WO 3 as a well-known prototypical system for studying polarons, which inherent polaronic nature is linked to its remark- able electrical and chromic properties. The primary objective of this research is to provide a comprehensive atomistic description and understanding of polaron formation in WO 3 using first-principles density functional theory (DFT) calcula- tions. Additionally, the investigation explores the interactions between polarons and the possibility of bipolaron formation. Following a systematic strategy, we first extensively analyze the dielectric and lattice dynamical properties of WO 3 in both the room-temperature P 2 1 /n and ground-state P 2 1 /c phases. Our specific focus is on characterizing the zone-center phonons, which serve as the founda- tion for identifying the phonon modes involved in the polaron formation and charge localization process. Subsequently, we examine the impact of structural distortions on the electronic structure of WO 3 to elucidate the interplay between structural distortions and electronic properties, thereby laying the groundwork for understanding electron-phonon couplings. By incorporating these critical fac- tors, we address our primary research goals. The most common explanation for the polaron formation is associated with the electrostatic screening of the extra charge by the polarizable lattice. Here, we show that, even in ionic crystals, this is not necessarily the case. We demonstrate that polarons in this compound arise primarily from non-polar atomic distortions. We then unveil that this unexpected behavior originates from the undoing of distortive atomic motions, which lowers the bandgap. As such, we coin the name of anti-distortive polaron and validate its appearance through a simple quantum-dot model, in which charge localization is the result of balancing structural, electronic, and confinement energy costs. Then, we also study the polaron-polaron interaction and present the formation of the antiferromagnetic W 4+ bipolaronic state with relatively large formation energy. Our analysis of the W 4+ bipolaronic distortions on the global structure reveals the same behavior as in experiments where the highly distorted monoclinic phase transforms into a tetragonal phase as a function of doping. Additionally, leveraging our previous findings on asymmetric polaronic distortion and examin- ing different merging orientations, we stabilize the antiferromagnetic W 5+ -W 5+ bipolaronic state with an energy lower than the W 4+ state. This thesis clari- fies the formation of unusual medium-size 2D polarons and bipolarons in WO3,which might be relevant to the whole family of ABO 3 perovskites, to which WO 3 is closely related. The simplicity of the concept provides also obvious guidelines for tracking similar behavior in other families of compounds. |
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Most recent IF: NA |
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Call Number |
UA @ admin @ c:irua:198169 |
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8868 |
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Hassani, H.; Partoens, B.; Bousquet, E.; Ghosez, P. |
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Title |
First-principles study of lattice dynamical properties of the room-temperature P2₁/n and ground-state P2₁/c phases of WO₃ |
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A1 Journal article |
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Year |
2022 |
Publication |
Physical review B |
Abbreviated Journal |
Phys Rev B |
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Volume |
105 |
Issue |
1 |
Pages |
014107 |
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Keywords |
A1 Journal article; Condensed Matter Theory (CMT) |
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Using first-principles density functional theory, we investigate the dynamical properties of the roomtemperature P21/n and ground-state P21/c phases of WO3. As a preliminary step, we assess the validity of various standard and hybrid functionals, concluding that the best description is achieved with the B1-WC hybrid functional while a reliable description can also be provided using the standard LDA functional. We also carefully rediscuss the structure and energetics of all experimentally observed and a few hypothetical metastable phases in order to provide deeper insight into the unusual sequence of phase transition of WO3 with temperature. Then, we provide a comprehensive theoretical study of the lattice dynamical properties of the P21/n and P21/c phases, reporting zone-center phonons, infrared and Raman spectra, as well as the full phonon dispersion curves, which attest to the dynamical stability of both phases. We carefully discuss the spectra, explaining the physical origin of their main features and evolution from one phase to another. We reveal a systematic connection between the dynamical and structural properties of WO3, highlighting that the number of peaks in the high-frequency range of the Raman spectrum appears as a fingerprint of the number of antipolar distortions that are present in the structure and a practical way to discriminate between the different phases. |
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000747398100004 |
Publication Date |
2022-01-24 |
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2469-9969; 2469-9950 |
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UA library record; WoS full record; WoS citing articles |
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Impact Factor |
3.7 |
Times cited |
5 |
Open Access |
Not_Open_Access |
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Most recent IF: 3.7 |
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Call Number |
UA @ admin @ c:irua:186388 |
Serial |
6994 |
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