Electronic structure and chemical bonding in transition-metal-mixed gallium oxide (Ga2O3) compounds

Ramana, C. V.; Roy, Swadipta; Zade, Vishal; Battu, Anil K.; Makeswaran, Nanthakishore; Shutthanandan, V.

doi:10.1016/j.jpcs.2021.110174

Cited by 28 publications

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References 75 publications

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“…X-ray photoelectron spectroscopy (XPS) is a very valuable analytical technique to investigate the electronic structure, chemical valence states, and qualitative analysis of various elements present in the samples. , In addition, it is possible to determine the cation distribution of the spinel ferrites through the deconvolution of the resultant XPS spectra of the sample . In the present study, XPS spectra of NFO, NMFO, and NIFO samples were recorded using carbon as an internal reference material, and the resultant survey spectra are shown in Figure .…”

Section: Resultsmentioning

confidence: 99%

“…The results and observations of XPS characteristic peaks with respect to various elements are in good agreement with the results of the EDS analysis. To extract further detailed information on individual elements (Fe, Ni, In, Mg) of the samples, high-resolution spectra of the elements were deconvoluted, using the standard procedures, , after correction using carbon 1s peak (284.6 eV).…”

Section: Resultsmentioning

confidence: 99%

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Tunable Dielectric Properties of Nickel Ferrite Derived via Crystallographic Site Preferential Cation Substitution

et al. 2022

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We report on the tunable dielectric properties achieved in cation-substituted nickel ferrite (NiFe 2 O 4 ; NFO) by selectively engineering the crystallographic site occupation of the dopant cation in the NFO ceramics. The NFO, Mg-substituted NFO (NiMg 0.2 Fe 1.8 O 4 ; NMFO), and In-substituted NFO (NiIn 0.2 Fe 1.8 O 4 ; NIFO) nanocrystals were synthesized by employing a tartrate-gel chemical route, followed by calcination at 500 °C. High-resolution transmission electron microscopy (HRTEM) analyses indicate the crystal quality of NFO, NMFO, and NIFO nanomaterials. The HRTEM data revealed that all of the ferrite materials were nanocrystalline with sizes in the range of 15−25 nm. Coupled with HRTEM analyses, X-ray diffraction analyses indicate the formation of single-phase spinel-structured NFO, NMFO, and NIFO materials without any detectable impurities. Chemical analysis performed using Mossbauer spectroscopy indicates that Mg 2+ occupies the octahedral site, while In 3+ preferably occupies the tetrahedral site of the spinel-structured NFO. The Fourier transform infrared (FTIR) absorption bands corresponding to metal−oxygen (M−O) intrinsic stretching vibration in the octahedral unit (MO 6 ) and the tetrahedral unit (MO 4 ), respectively, were noted in all of the samples. However, the trend in the frequency shift of these bands in Mg-and In-substituted NFO materials is different due to the occupation of different sites of Mg and In as confirmed by Mossbauer studies. The electronic structure and chemical valence state analysis using X-ray photoelectron spectroscopy (XPS) corroborates with chemical bonding analyses performed by FTIR and cation distribution evaluation carried out by Mossbauer spectroscopy. The energy-dispersive X-ray spectrometry (EDS) data, in addition to XPS and FTIR analyses, further validate the formation of uniform and chemically homogeneous samples. The corresponding cation distribution revealed from Mossbauer studies correlates with the variation of dielectric properties of the doped NFO samples with respect to intrinsic NFO. At room temperature, the dielectric constant (ε) of NFO and NMFO is found to be nearly the same and constant over a wide range of frequencies. However, in NIFO, ε decreases with the applied frequency. The differences are attributed to the size effect and site preference of dopants (Mg 2+ and In 3+ ). Irrespective of the dopants, an increase in the temperature enhances the dielectric constant, which is due to an increase in the number of free charge carriers. A thermally activated electrical conduction mechanism was operative in NFO, NMFO, and NIFO materials. The activation energies for NFO, NFMO, and NIFO were 18.84, 34.48, and 57.14 meV, respectively. The enhanced dipolar effect of In 3+ at the tetrahedral site compared to Mg 2+ at the octahedral site may be the origin of the relatively higher value of activation energy in NIFO compared to intrinsic and Mg-substituted NFO.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Tunable Dielectric Properties of Nickel Ferrite Derived via Crystallographic Site Preferential Cation Substitution

et al. 2022

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“…It has been reported in the literature that the O 1s peak for the stoichiometric, undoped Ga 2 O 3 occurs generally at BE ∼ 530.5–531.0 eV. 56 , 57 Comparison of the O 1s peak data indicates that the O 1s peak position occurs at a well-defined BE. Also, there is no appreciable peak shift in the BE position.…”

Section: Resultsmentioning

confidence: 92%

Crystallization, Phase Stability, Microstructure, and Chemical Bonding in Ga₂O₃ Nanofibers Made by Electrospinning

et al. 2022

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We report on the crystal structure, phase stability, surface morphology, microstructure, chemical bonding, and electronic properties of gallium oxide (Ga 2 O 3 ) nanofibers made by a simple and economically viable electrospinning process. The effect of processing parameters on the properties of Ga 2 O 3 nanofibers were evaluated by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Thermal treatments in the range of 700–900 °C induce crystallization of amorphous fibers and lead to phase stabilization of α-GaOOH, β-Ga 2 O 3 , or mixtures of these phases. The electron diffraction analyses coupled with XPS indicate that the transformation sequence progresses by forming amorphous fibers, which then transform to crystalline fibers with a mixture of α-GaOOH and β-Ga 2 O 3 at intermediate temperatures and fully transforms to the β-Ga 2 O 3 phase at higher temperatures (800–900 °C). Raman spectroscopic analyses corroborate the structural evolution and confirm the high chemical quality of the β-Ga 2 O 3 nanofibers. The surface analysis by XPS studies indicates that the hydroxyl groups are present for the as-synthesized samples, while thermal treatment at higher temperatures fully removes those hydroxyl groups, resulting in the formation of β-Ga 2 O 3 nanofibers.

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“…Further, β-Ga 2 O 3 is stabilized in monoclinic crystal symmetry with the C2/m space group at ambient conditions. [39][40][41] The prepared β-Ga 2 O 3 and Sn x -Ga 2 O 3 samples were analyzed using different microscopic and spectroscopic techniques to confirm the Sn doping and derive an in-depth understanding of their morphology, structure, and surface chemistry. We recently reported a detailed account of crystallography, Rietveld refinement, structure, and surface morphology of the Sn-doped Ga 2 O 3 .…”

Section: Structure and Chemistrymentioning

confidence: 99%

Lewis Acid Site Assisted Bifunctional Activity of Tin Doped Gallium Oxide and Its Application in Rechargeable Zn‐Air Batteries

Nair

Sanad

Jayan

et al. 2022

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as future power sources due to their remarkably high theoretical energy output. [1][2][3][4] For instance, Zinc-air batteries are predicted to have a high theoretical specific energy density of 1086 W h kg −1 , which is 2.5 times higher than state-ofthe-art lithium-ion batteries. [5][6][7][8] The key to the functioning of Zn-air batteries is two electrochemical reactions occurring at the air cathode, namely oxygen reduction reaction (ORR) during discharging and oxygen evolution reaction (OER) during charging. Consequently, the inferior performance of the air cathode leads to the Zinc-air batteries displaying lower energy output than the theoretical value. Hence, catalysts with excellent catalytic efficacy towards ORR (e.g., Pt) and OER (e.g., RuO 2 ) are employed in the air cathode to enhance the performance of Zn-air batteries. However, the poor stability, high cost, and scarcity of state-of-the-art catalysts such as Pt or RuO 2 make the technology commercially untenable. Thus, the widespread adoption of Zinc-air batteries depends on discovering low-cost, highly active, stable, and potentially bifunctional electrocatalysts. Recently, transition metal oxide (TMO) systems emerged as viable ORR and OER electro catalysts due to their competentThe enhanced safety, superior energy, and power density of rechargeable metal-air batteries make them ideal energy storage systems for application in energy grids and electric vehicles. However, the absence of a cost-effective and stable bifunctional catalyst that can replace expensive platinum ( Pt)-based catalyst to promote oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at the air cathode hinders their broader adaptation. Here, it is demonstrated that Tin (Sn) doped β-gallium oxide (β-Ga 2 O 3 ) in the bulk form can efficiently catalyze ORR and OER and, hence, be applied as the cathode in Zn-air batteries. The Sn-doped β-Ga 2 O 3 sample with 15% Sn (Sn x=0.15 -Ga 2 O 3 ) displayed exceptional catalytic activity for a bulk, non-noble metal-based catalyst. When used as a cathode, the excellent electrocatalytic bifunctional activity of Sn x=0.15 -Ga 2 O 3 leads to a prototype Zn-air battery with a high-power density of 138 mW cm −2 and improved cycling stability compared to devices with benchmark Pt-based cathode. The combined experimental and theoretical exploration revealed that the Lewis acid sites in β-Ga 2 O 3 aid in regulating the electron density distribution on the Sn-doped sites, optimize the adsorption energies of reaction intermediates, and facilitate the formation of critical reaction intermediate (O*), leading to enhanced electrocatalytic activity.

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Electronic structure and chemical bonding in transition-metal-mixed gallium oxide (Ga2O3) compounds

Cited by 28 publications

References 75 publications

Tunable Dielectric Properties of Nickel Ferrite Derived via Crystallographic Site Preferential Cation Substitution

Tunable Dielectric Properties of Nickel Ferrite Derived via Crystallographic Site Preferential Cation Substitution

Crystallization, Phase Stability, Microstructure, and Chemical Bonding in Ga₂O₃ Nanofibers Made by Electrospinning

Lewis Acid Site Assisted Bifunctional Activity of Tin Doped Gallium Oxide and Its Application in Rechargeable Zn‐Air Batteries

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Electronic structure and chemical bonding in transition-metal-mixed gallium oxide (Ga2O3) compounds

Cited by 28 publications

References 75 publications

Tunable Dielectric Properties of Nickel Ferrite Derived via Crystallographic Site Preferential Cation Substitution

Tunable Dielectric Properties of Nickel Ferrite Derived via Crystallographic Site Preferential Cation Substitution

Crystallization, Phase Stability, Microstructure, and Chemical Bonding in Ga2O3 Nanofibers Made by Electrospinning

Lewis Acid Site Assisted Bifunctional Activity of Tin Doped Gallium Oxide and Its Application in Rechargeable Zn‐Air Batteries

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Crystallization, Phase Stability, Microstructure, and Chemical Bonding in Ga₂O₃ Nanofibers Made by Electrospinning