Sol–gel synthesis and characterization of the delafossite CuAlO2

Abstract

Nanocrystalline CuAlO 2 is synthesized by solgel method using ethylene glycol as solvent. The stages of formation are followed by thermal analysis. The X-ray diffraction pattern of the powder heat-treated at 1100°C shows a single phase, indexed in a rhombohedral symmetry (R 3 m). The apparent crystallite size (57 ± 8 nm) is determined from the Williamson-Hall plot. The direct optical transition (=3.69 eV), evaluated from the diffuse reflectance spectrum, is attributed to the charge transfer (O 2-: 2p ? Cu ? : 4s). The oxide is p-type semiconductor, and the conduction occurs predominantly by small polaron hopping between mixed valences Cu 2?/? , due to oxygen insertion in the layered crystal. The photoelectrochemical characterization gives a flat band of 0.20 V SCE and a hole density of 1.13 9 10 18 cm -3 . The semicircle centered on the real axis, in the electrochemical impedance spectroscopy (EIS), is due to the absence of constant phase element with a pure capacitive behavior. The straight line at 35°at low frequencies is attributed to the diffusion in the layered structure. Graphical Abstract Temperature dependence of the electrical conductivity for CuAlO 2 synthesized by sol-gel method. Inset: the variable range hopping at low temperatures. The sol-gel method has been successfully employed for the preparation of CuAlO 2 . The thermal variation of the conductivity indicates a semiconducting behavior which is frequency independent. At low temperature, a variable range hopping involves electrons jump over large distances according to the Mott law r ¼ r 0 exp T 0 T À Á 0:25 .

New insights into intrinsic point defects of delafossite CuAlO2 as optoelectronic materials

“…As shown in Figures 5I and 6I, similar to the case of antisite Al Cu defect, interstitial O i defect also produces an occupied energy band with a distance of 0.205 eV above VBM and an unoccupied energy band with a distance of 1.119 eV below CBM. If it is charged by +1 state, the former can act as shallow acceptor‐type level and results in p‐type conductivity, which is consistent with Benreguia et al.’s findings, in which oxygen inserts into the layered space of CuAlO 2 38 . The latter can act as the recombination center for the photo‐generated electron–hole pairs.…”

“…If it is charged by +1 state, the former can act as shallow acceptor-type level and results in p-type conductivity, which is consistent with Benreguia et al's findings, in which oxygen inserts into the layered space of CuAlO 2 . 38 The latter can act as the recombination center for the photo-generated electronhole pairs. The 2p states of interstitial O atom do not contribute to its composition, indicating that it belongs to the delocalized electronic states.…”

Synthesis and Characterization of ZnBi2O4 Nanoparticles: Photocatalytic Performance for Antibiotic Removal under Different Light Sources

“…(Figure 8 The process is also represented in the Bode plan (log Z vs. log frequency) (Figure S9 in the Supplementary Data). The decrease in Z increasing the frequency indicates an enhanced electrical conductivity and a lowering of the potential barrier [57].…”

“…The location of electronic bands has great importance for the prediction of interfacial reactions in photocatalysis, and it is located using the flat band potential. The flat band potential is determined from the capacitance-potential plot using the Mott-Schottky relation [57]:…”

“…The process is also represented in the Bode plan (log Z vs. log frequency) (Figure S9 in the Supplementary Data). The decrease in Z increasing the frequency indicates an enhanced electrical conductivity and a lowering of the potential barrier [57]. The diagram of electrochemical impedance spectroscopy (EIS) of the junction ZnBi 2 O 4 / NaOH electrolyte is modeled to an equivalent electrical circuit using the software Zview (Figure 8 Inset), corresponding to the contribution of the bulk, grains boundary, and ions diffusion.…”