Photovoltaic (PV) effects, power-conversion efficiencies, and structures have been systematically measured in (Bi 1Àx Ca x)FeO 3Àd ceramics for x ¼ 0.05, 0.10, and 0.15. The heterostructures of indium tin oxide (ITO) film/(Bi 1Àx Ca x)FeO 3Àd ceramics/Au film exhibit significant PV effects under illumination of k ¼ 405 nm. The maximum power-conversion efficiency in the ITO/(Bi 0.90 Ca 0.10)FeO 2.95 (BFO10C)/Au can reach 0.0072%, which is larger than 0.0025% observed in the graphene/polycrystalline BFO/Pt films [Zang et al., Appl. Phys. Lett. 99, 132904 (2011)]. A theoretical model based on optically excited current in the depletion region between ITO film and Ca-doped BFO ceramics is used to describe the I-V characteristic, open-circuit voltage, and short-circuit current density as a function of illumination intensity. This work suggests that the Ca-substitution can reduce the rhombohedral distortion and stabilize the single-phase structure. V

Micro-Raman spectroscopy, X-ray diffraction, high-resolution transmission electron microscopy (TEM), oxygen vacancies, synchrotron X-ray absorption spectroscopy, magnetizations, optical band gaps, and photovoltaic (PV) effects have been studied in (Bi 1 -x La x )FeO 3 (BFO100xL) ceramics for x = 0.0, 0.05, 0.10, and 0.15. XRD, Raman spectra, and TEM confirm a rhombohedral R3c symmetry with the tilted FeO 6 oxygen octahedra in all compounds. The low-frequency Raman vibrations become broader and shift toward higher frequency as La 3+ increases. Fe K-edge synchrotron X-ray absorptions reveal that Fe

Raman spectroscopy, X-ray diffraction (XRD), magnetization hysteresis loop, synchrotron X-ray absorption spectroscopy, and photovoltaic effects have been measured in (Bi 1 À x Sr x )FeO 3 À δ (BFO100xSr) ceramics for x ¼0.0, 0.05, 0.10, and 0.15. Raman spectra and XRD reveal a rhombohedral R3c structure in all compounds. A-site Sr 2 þ doping increases fluctuations in cation-site occupancy and causes broadening in Raman modes. BFO15Sr exhibits a strong ferromagnetic feature due to reduction of Fe-O-Fe bond angle evidenced by the extended synchrotron X-ray absorption fine structure. The heterostructure of indium tin oxide (ITO) film/(Bi 1 À x Sr x )FeO 3 À δ ceramic/Au film exhibit clear photovoltaic (PV) responses under blue illumination of λ¼ 405 nm. The maximal power-conversion efficiency and external quantum efficiency in ITO/ BFO5Sr/Au are about 0.004% and 0.2%, respectively. A model based on optically excited charges in the depletion region between ITO and (Bi 1 À x Sr x )FeO 3 À δ can well describe open-circuit voltage and short-circuit current as a function of illumination intensity.

Spontaneous magnetization and photovoltaic (PV) effects have been measured in (Bi 1-x Ba x)FeO 3-d ceramics for x ¼ 0.05, 0.10, and 0.15. The substitution of Ba 2þ ion in the A site of the perovskite unit cell can effectively enhance the ferromagnetic magnetization. The heterostructure of indium tin oxide (ITO) film/(Bi 1-x Ba x)FeO 3-d ceramic/Au film exhibits significant PV effects under illumination of k ¼ 405 nm. The PV responses decrease with increasing Ba concentration. The maximum power-conversion efficiency in the ITO/(Bi 0.95 Ba 0.5)FeO 2.95 /Au can reach 0.006%. A theoretical model based on optically excited current in the depletion region between ITO film and (Bi 1-x Ba x)FeO 3-d ceramics is used to describe the I-V characteristic, open-circuit voltage (V oc), and short-circuit current density (J sc) as a function of light intensity. V

A green method for synthesizing Pd nanoparticles/graphene composites from a choline chloride–oxalic acid deep eutectic solvent (DES) without a reducing agent or a surfactant is reported. Deep eutectic solvents are usually composed of halide salts and hydrogen-bond donors, and many are biocompatible and biodegradable. The merits of deep eutectic solvents include that they serve as reducing agents and dispersants, and Pd nanoparticles are tightly anchored to graphene. The size and dispersion of Pd particles are improved when supercritical carbon dioxide (scCO 2 ) is used because it has gaslike diffusivity and near-zero surface tension, which results in excellent wettability between the scCO 2 and the carbon surface. The prepared sc-Pd NPs/GR/SPCE shows excellent activity toward glycerol oxidation compared to composites not fabricated by scCO 2 processes. This study demonstrates the potential of using this scCO 2 -assisted protocol combined with deep eutectic solvents to further construct nanoparticles/graphene composites.