Investigation of Iron Doped Gallium Oxide (Ga-Fe-O) System: Structure Property Relationship and Performance Evaluation for Optical and Catalytic Applications
We report on the optimized synthesis conditions of iron (Fe)-doped gallium oxide (Ga2O3; Ga1.9Fe0.1O3, referred to as GFO) inorganic compounds. The GFO materials were synthesized using a standard high-temperature solid-state chemical reaction method by maintaining the Fe doping amount constant. X-ray diffraction (XRD) revealed that GFO compounds crystallize in the β-Ga2O3 phase. The effect of the sintering temperature (Tsint), which was varied in the range of 900–1200 °C, is significant, as revealed by scanning electron microscopy (SEM) analysis. Tsint influences the grain size and microstructure evolution, which, in turn, influences the dielectric properties of GFO compounds. The energy-dispersive X-ray spectrometry (EDS) data demonstrate the uniform distribution of the elemental composition over the microstructure. The temperature and frequency-dependent dielectric measurements indicate the characteristic features that are specifically due to Fe doping in Ga2O3. The results demonstrate that densification and control over the microstructure and properties of GFO can be achieved by optimizing Tsint. New sets of GFO compounds were synthesized by varying the iron (Fe)-doping amount (i.e., Ga2–xFexO3; x= 0.00 – 0.30) following the standard high-temperature (Tsint: 1200 °C) solid-state chemical reaction method. XRD studies of the sintered compounds provided evidence for the Fe3+ substitution at Ga3+ site without any secondary phase formation. Rietveld refinement of XRD patterns reveal that the GFO compounds crystallized in monoclinic crystal symmetry. X-ray photoelectron spectroscopy (XPS) data revealed that at lower concentrations of doping, Fe exhibited mixed chemical valence states, whereas single chemical valence state was evident for higher Fe content. Local structure and chemical bonding analyses using X-ray absorption near edge structure (XANES) revealed that the Fe occupied octahedral and tetrahedral sites similar to Ga in parent Ga2O3 lattice without considerable changes in the local symmetry. Raman spectroscopy also confirmed the crystalline nature of the GFO compounds. Morphology of the GFO compounds was characterized by the presence of rod-shaped particle features employing SEM. The EDS confirmed the chemical stoichiometry of the GFO compounds, where the atomic ratio of the constituted elements was in accordance with the calculated concentration values. Optical absorption spectra revealed a significant red shift in the optical band gap with Fe doping. Origin of the significant red shift is attributed to the strong sp-d exchange interaction originated from the 3d5 electrons of Fe3+. Coupled with optical band gap red shift, electrocatalytic studies of GFO compounds revealed that doped Ga2O3 compound exhibited electrocatalytic activity in contrast to intrinsic Ga2O3. Fe doped samples demonstrated appreciable electrocatalytic activity towards the generation of H2 through electrocatalytic water splitting. Electrocatalytic activity of the GFO compounds is attributed to cumulative effect of different mechanisms such as doping resulted new catalytic centers, enhanced conductivity, and electron mobility. Hence, a new pathway in which electrocatalytic behavior of the GFO compounds resulted due to Fe chemical states, red shift in optical band gap was explored for the very first time. 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.
Roy, Swadipta, "Investigation of Iron Doped Gallium Oxide (Ga-Fe-O) System: Structure Property Relationship and Performance Evaluation for Optical and Catalytic Applications" (2020). ETD Collection for University of Texas, El Paso. AAI27999895.