Crystal Chemistry, Band-Gap Red Shift, and Electrocatalytic Activity of Iron-Doped Gallium Oxide Ceramics

Abstract

This work for the first time unfurls the fundamental mechanisms and sets the stage for an approach to derive electrocatalytic activity, which is otherwise not possible, in a traditionally known wide band-gap oxide material. Specifically, we report on the tunable optical properties, in terms of wide spectral selectivity and red-shifted band gap, and electrocatalytic behavior of iron (Fe)-doped gallium oxide (β-Ga2O3) model system. X-ray diffraction (XRD) studies of sintered Ga2–x Fe x O3 (GFO) (0.0 ≤ x ≤ 0.3) compounds provide evidence for the Fe3+ substitution at Ga3+ site without any secondary phase formation. Rietveld refinement of XRD patterns reveals that the GFO compounds crystallize in monoclinic crystal symmetry with a C2/m space group. The electronic structure of the GFO compounds probed using X-ray photoelectron spectroscopy data reveals that at lower concentrations, Fe exhibits mixed chemical valence states (Fe3+, Fe2+), whereas single chemical valence state (Fe3+) is evident for higher Fe content (x = 0.20–0.30). The optical absorption spectra reveal a significant red shift in the optical band gap with Fe doping. The origin of the significant red shift even at low concentrations of Fe (x = 0.05) is attributed to the strong sp–d exchange interaction originated from the 3d5 electrons of Fe3+. The optical absorption edge observed at ≈450 nm with lower intensity is the characteristic of Fe-doped compounds associated with Fe3+–Fe3+ double-excitation process. Coupled with an optical band-gap red shift, electrocatalytic studies of GFO compounds reveal that, interestingly, Fe-doped Ga2O3 compound exhibits electrocatalytic activity in contrast to intrinsic Ga2O3. Fe-doped samples (GFO) demonstrated appreciable electrocatalytic activity toward the generation of H2 through electrocatalytic water splitting. An onset potential and Tafel slope of GFO compounds include ∼900 mV, ∼210 mV dec–1 (x = 0.15) and ∼1036 mV, ∼290 mV dec–1 (x = 0.30), respectively. The electrocatalytic activity of Fe-doped Ga-oxide compounds is attributed to the cumulative effect of different mechanisms such as doping resulting in new catalytic centers, enhanced conductivity, and electron mobility. Hence, in this report, for the first time, we explored a new pathway; the electrocatalytic behavior of Fe-doped Ga2O3 resulted due to Fe chemical states and red shift in the optical band gap. The implications derived from this work may be applicable to a large class of compounds, and further options may be available to design functional materials for electrocatalytic energy production.

Surface Photovoltage Spectroscopy over Wide Time Domains for Semiconductors with Ultrawide Bandgap: Example of Gallium Oxide

“…The situation will be even more complex for the engineering of electronic transitions and bandgaps by alloying Ga 2 O 3 , for example with aluminum, [31] iron, [32] or titanium. [33] But nevertheless, related samples can be studied by the nonconventional approach of SPV measurements proposed in this work. For example, several transition energies and broadening parameters have been obtained or estimated for β-Ga 2 O 3 by fitting positive and negative slopes of transient and modulated SPV spectra in the AC regime.…”

Electronic Structure, Chemical Bonding, and Electrocatalytic Activity of Ba(Fe0.7Ta0.3)O3−δ Compounds

“…39 Furthermore, in our recent work, we reported an approach to derive electrocatalytic activity, which is otherwise not possible, in oxide materials. 40 Iron-mixed Ga-oxide demonstrated appreciable electrocatalytic activity toward the generation of H 2 through electrocatalytic water splitting. 40 The electrocatalytic activity of Fe-doped Ga-oxide compounds is attributed to the cumulative effect of different mechanisms, such as Fe-doping induced new catalytic centers and enhanced conductivity due to Fe chemical states.…”

“…40 Iron-mixed Ga-oxide demonstrated appreciable electrocatalytic activity toward the generation of H 2 through electrocatalytic water splitting. 40 The electrocatalytic activity of Fe-doped Ga-oxide compounds is attributed to the cumulative effect of different mechanisms, such as Fe-doping induced new catalytic centers and enhanced conductivity due to Fe chemical states. 40 In view of these considerations, the present work was focused toward the synthesis, electronic structure determination, and electrocatalytic activity evaluation of Fe, Ta co-doped BFTO compounds.…”

“…40 The electrocatalytic activity of Fe-doped Ga-oxide compounds is attributed to the cumulative effect of different mechanisms, such as Fe-doping induced new catalytic centers and enhanced conductivity due to Fe chemical states. 40 In view of these considerations, the present work was focused toward the synthesis, electronic structure determination, and electrocatalytic activity evaluation of Fe, Ta co-doped BFTO compounds. From electrocatalysis point of view, the scientific merit and significance of the present work can be further understood as follows.…”

Chemical composition tuning induced variable and enhanced dielectric properties of polycrystalline Ga2‐2xWxO3 ceramics

“…14,18 The electrical breakdown voltage is exceptionally high 8 MV/cm, which in comparison to SiC and GaN, 2.5 and 3.3 MV/cm, respectively, is in multiples. 13,19,20 These properties make -Ga 2 O 3 a suitable candidate for a wide variety of energy, electronic, power, optoelectronics, and catalysis applications, which include solar blind UV-photodetectors, 5,12,14,21 light emitting diodes (LEDs) , 22,23 transparent conducting oxide electrodes (TCOs) , 24,25 photo-and electro-catalysts, [26][27][28] high-temperature sensors, 29,30 high power electronic devices [11][12][13][14]31,32 with a potential to dwarf the existing SiN, Si and GaN devices in terms of performance. On the other hand, the potential for Ga 2 O 3 to derive new properties and phenomena, which can facilitate designing materials especially for energy related applications, is continually evolving.…”