High-Pressure Structural Transitions of Sc<sub>2</sub>O<sub>3</sub> by X-ray Diffraction, Raman Spectra, and Ab Initio Calculations

Liu, Dan; Lei, Weiwei; Li, Yinwei; Ma, Yanming; Hao, Jian; Chen, Xiaohui; Jin, Yang; Liu, Dedi; Shen, Yu; Cui, Qiliang; Zou, Guangtian

doi:10.1021/ic900889v

Cited by 54 publications

(45 citation statements)

References 44 publications

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“…A 4x4x4 k-point mesh was used for the 1x1x1 (40 atoms) primitive cell of Sc 2 O 3 . At higher k-point densities of 5x5x5 or greater for the 40 atom cell the total energy differed by less than 1 meV/formula unit compared to the 4x4x4 k-point mesh, which is consistent with previous ab initio studies on bulk bixbyite Sc 2 O 3 29,47. For larger supercell slabs, the k-point…”

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confidence: 88%

Electron Emission Energy Barriers and Stability of Sc₂O₃ with Adsorbed Ba and Ba–O

2014

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In this study we employ Density Functional Theory (DFT) methods to investigate the surface energy barrier for electron emission (surface barrier) and thermodynamic stability of Ba and Ba-O species adsorption (relative to formation of bulk BaO) under conditions of high temperature (approximately 1200 K) and low pressure (approximately 10 -10 Torr) on the low index surfaces of bixbyite Sc 2 O 3 . We employ both the standard Generalized Gradient Approximation (GGA) and the hybrid HSE functional to calculate accurate surface barriers from relaxed GGA structures. The role of Ba in lowering the cathode surface barrier is investigated via adsorption of atomic Ba and Ba-O dimers, where the highest simulated dimer coverage corresponds to a single monolayer film of rocksalt BaO. The change of the surface barrier of a semiconductor due to adsorption of surface species is decomposed into two parts: a surface dipole component and doping 2 component. The dipole component is the result of charge rearrangement at the surface and is described by the electrostatic Helmholtz equation. The doping component is due to charge transfer from the surface species, which changes the Fermi level and thereby changes the surface barrier. Different initial geometries, adsorption sites, and coverages were tested for the most stable low index Sc 2 O 3 surfaces ((011) and (111)) for both atomic Ba and Ba-O dimers. The lowest surface barrier with atomic Ba on Sc 2 O 3 was found to be 2.12 eV and 2.04 eV for the (011) and (111) surfaces at 3 and 1 Ba atoms per surface unit cell (0.250 and 0.083 Ba per surface O), respectively. The lowest surface barrier for Ba-O on Sc 2 O 3 was found to be 1.21 eV on (011) for a 7 Ba-O dimer-per-unit-cell coverage (0.583 dimers per surface O). Generally, we found that Ba in its atomic form on Sc 2 O 3 surfaces is not stable relative to bulk BaO, while Ba-O dimer coverages between 3 to 7 Ba-O dimers per (011) surface unit cell (0.250 to 0.583 dimers per surface O) produce stable structures relative to bulk BaO. Ba-O dimer adsorption on Sc 2 O 3 ( 111) surfaces was found to be unstable versus BaO over the full range of coverages studied. Investigation of combined n-type doping and surface dipole modification showed that their effects interact to yield a reduction less than the two contributions would yield separately.

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confidence: 88%

Electron Emission Energy Barriers and Stability of Sc₂O₃ with Adsorbed Ba and Ba–O

2014

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“…So ignorance of the temperature parameters brings about the large discrepancy of pressure. 41,42 The calculation overestimates the pressure, we only show the high-pressure changing trends of the structure. During the calculation, distortion trend becomes more and more obvious during the compression.…”

Section: Resultsmentioning

confidence: 87%

Compression studies of face-to-face π-stacking interaction in sodium squarate salts: Na2C4O4 and Na2C4O4•3H2O

Wang

et al. 2012

The Journal of Chemical Physics

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High-pressure Raman scattering and synchrotron X-ray diffraction measurements of sodium squarate (Na(2)C(4)O(4), SS) are performed in a diamond anvil cell. SS possesses a rare, but typical structure, which can show the effect of face-to-face π-stacking without interference of other interactions. At ~11 GPa, it undergoes a phase transition, identified as a symmetry transformation from P2(1)/c to P2(1). From high-pressure Raman patterns and the calculated model of SS, it can be proved that the phase transition results from the distorted squarate rings. We infer it is the enhancement of π-stacking that dominates the distortion. For comparison, high-pressure Raman spectra of sodium squarate trihydrate (Na(2)C(4)O(4)●3H(2)O, SST) are also investigated. The structure of SST is determined by both face-to-face π-stacking and hydrogen bonding. SST can be regarded as a deformation of SS. A phase transition, with the similar mechanism as SS, is observed at ~10.3 GPa. Our results can be well supported by the previous high-pressure studies of ammonium squarate ((NH(4))(2)C(4)O(4), AS), and vice versa. High-pressure behaviors of the noncovalent interactions in SS, SST, and AS are compared to show the impacts of hydrogen bonding and the role of electrostatic interaction in releasing process.

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“…All rare earth sesquioxides can be obtained in their ground-state C-type structure at room temperature. The B-type structure is both a high pressure and a high temperature phase for sesquioxides from Sm to Ho, and high pressure phase for sesquioxides from Er to Lu, Y and Sc [ 85 , 86 , 87 , 88 ]. In Figure 5 , volumes of C and B phases for samples studied in this work are plotted vs. average ionic radius together with volumes of pure sesquioxides.…”

Section: Discussionmentioning

confidence: 99%

Thermal Analysis of High Entropy Rare Earth Oxides

et al. 2020

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Phase transformations in multicomponent rare earth sesquioxides were studied by splat quenching from the melt, high-temperature differential thermal analysis and synchrotron X-ray diffraction on laser-heated samples. Three compositions were prepared by the solution combustion method: (La,Sm,Dy,Er,RE)2O3, where all oxides are in equimolar ratios and RE is Nd or Gd or Y. After annealing at 800 °C, all powders contained mainly a phase of C-type bixbyite structure. After laser melting, all samples were quenched in a single-phase monoclinic B-type structure. Thermal analysis indicated three reversible phase transitions in the range 1900–2400 °C, assigned as transformations into A, H, and X rare earth sesquioxides structure types. Unit cell volumes and volume changes on C-B, B-A, and H-X transformations were measured by X-ray diffraction and consistent with the trend in pure rare earth sesquioxides. The formation of single-phase solid solutions was predicted by Calphad calculations. The melting point was determined for the (La,Sm,Dy,Er,Nd)2O3 sample as 2456 ± 12 °C, which is higher than for any of constituent oxides. An increase in melting temperature is probably related to nonideal mixing in the solid and/or the melt and prompts future investigation of the liquidus surface in Sm2O3-Dy2O3, Sm2O3-Er2O3, and Dy2O3-Er2O3 systems.

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High-Pressure Structural Transitions of Sc₂O₃ by X-ray Diffraction, Raman Spectra, and Ab Initio Calculations

Cited by 54 publications

References 44 publications

Electron Emission Energy Barriers and Stability of Sc₂O₃ with Adsorbed Ba and Ba–O

Electron Emission Energy Barriers and Stability of Sc₂O₃ with Adsorbed Ba and Ba–O

Compression studies of face-to-face π-stacking interaction in sodium squarate salts: Na2C4O4 and Na2C4O4•3H2O

Thermal Analysis of High Entropy Rare Earth Oxides

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High-Pressure Structural Transitions of Sc2O3 by X-ray Diffraction, Raman Spectra, and Ab Initio Calculations

Cited by 54 publications

References 44 publications

Electron Emission Energy Barriers and Stability of Sc2O3 with Adsorbed Ba and Ba–O

Electron Emission Energy Barriers and Stability of Sc2O3 with Adsorbed Ba and Ba–O

Compression studies of face-to-face π-stacking interaction in sodium squarate salts: Na2C4O4 and Na2C4O4•3H2O

Thermal Analysis of High Entropy Rare Earth Oxides

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High-Pressure Structural Transitions of Sc₂O₃ by X-ray Diffraction, Raman Spectra, and Ab Initio Calculations

Electron Emission Energy Barriers and Stability of Sc₂O₃ with Adsorbed Ba and Ba–O

Electron Emission Energy Barriers and Stability of Sc₂O₃ with Adsorbed Ba and Ba–O