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Electronic structure and optical properties of BaMoO4 powders
J.C. Sczancoski,L.S. Cavalcante,N.L. Marana,R.O. da Silva,R.L. Tranquilin,M.R. Joya,P.S. Pizani,J.A. Varela,J.R. Sambrano,M. Siu Li,E. Longo,J. Andrés 한국물리학회 2010 Current Applied Physics Vol.10 No.2
Barium molybdate (BaMoO4) powders were synthesized by the co-precipitation method and processed in microwave-hydrothermal at 140 ℃ for different times. These powders were characterized by X-ray diffraction (XRD), Fourier transform Raman (FT-Raman), Fourier transform infrared (FT-IR), ultraviolet–visible (UV–vis) absorption spectroscopies and photoluminescence (PL) measurements. XRD patterns and FT-Raman spectra showed that these powders present a scheelite-type tetragonal structure without the presence of deleterious phases. FT-IR spectra exhibited a large absorption band situated at around 850.4 cm1, which is associated to the Mo–O antisymmetric stretching vibrations into the [MoO4] clusters. UV–vis absorption spectra indicated a reduction in the intermediary energy levels within band gap with the processing time evolution. First-principles quantum mechanical calculations based on the density functional theory were employed in order to understand the electronic structure (band structure and density of states) of this material. The powders when excited with different wavelengths (350 nm and 488 nm) presented variations. This phenomenon was explained through a model based in the presence of intermediary energy levels (deep and shallow holes) within the band gap.
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R. C. Silva,A. F. Gouveia,J. C. Sczancoski,R. S. Santos,J. L. S. Sá,E. Longo,L. S. Cavalcante 대한금속·재료학회 2019 ELECTRONIC MATERIALS LETTERS Vol.15 No.5
This letter reports the synthesis of RuO2nanocrystals by the anionic surfactant-assisted hydrothermal method at 90 °C for24 h followed by heat treatment at 500 °C for 1 h. These crystals were structurally characterized by means of X-ray diffraction(XRD) and Rietveld refinement analysis. Field emission scanning electron microscopy (FE-SEM) was employed to observethe morphological features these crystals. The optical behavior was investigated by ultraviolet–visible (UV–Vis) spectroscopy. First-principles quantum mechanical calculations based on the density functional theory at the B3LYP level wereemployed to obtain the electronic band structure and density of states. For electrochemical behavior, the supercapacitorproperties of RuO2crystals were investigated by cyclic voltammetry. XRD patterns and Rietveld refinement data indicatethat RuO2crystals have a rutile-type tetragonal structure. FE-SEM images showed the presence of sphere-like RuO2crystalswith an average crystal sized at around 19.13 nm. The experimental band gap energy (Egap[exp]) was estimated at 2.60 eV byusing UV–Vis spectroscopy, while the theoretical calculations indicate an Egap[theo] at 1.92 eV. These calculations revealed aband structure predominantly composed of O 2p orbitals (valence band) and Ru 4d orbitals (conduction band). The specificcapacitance measured for RuO2film was 193 F g−1 at 5 mV s−1 in an electrode with 0.5 mg of electroactive material in 1 MNa2SO4solution.
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