RESUMEN
Bi5Ti3FeO15 (pentabismuth trititanium iron pentadecaoxide), which is a multiferroic four-layer Aurivillius phase compound, has received much attention in recent years. However, three mutually inconsistent orthorhombic space groups, i.e. A21am, Fmm2 and Pnn2, have been reported for the room-temperature phase of Bi5Ti3FeO15 by X-ray and neutron diffraction investigations. Here, electron diffraction results are presented and discussed for the first time to unambiguously clarify the room-temperature space group of ceramic Bi5Ti3FeO15. It has been found that all the observed reflections from the ceramic agree with those expected in A21am, while the observed reflections 011, 013 and 015 should be forbidden in the case of Fmm2, and no 107 and 109 reflections were observed although allowed for Pnn2. The present study has demonstrated that the space group of Bi5Ti3FeO15 ceramic is A21am rather than Fmm2 or Pnn2, an identification that proved to be a challenge for X-ray diffraction. On the basis of the space group A21am, the lattice parameters of the Bi5Ti3FeO15 ceramic were calculated from its X-ray diffraction data.
RESUMEN
The unique piezoelectric potential of piezoelectrics could lead to performance gains for electrochemical catalysis. Here, a cuboid-like Na0.5Bi0.5TiO3 (NBTO) piezoelectric micron crystal was synthesized by a hydrothermal process. The piezocatalytic and visible light assisted piezo-photocatalytic activities of NBTO were investigated. Surprisingly, under ultrasonic vibration and visible light irradiation, the NBTO exhibited four times faster degradation rate than that under ultrasonic vibration only, although the NBTO doesn't absorb visible light. An efficient coupling between piezoelectric effect and visible light photoexcitation in NBTO was directly demonstrated. The improved piezo-photocatalytic performance is attributed to the piezoelectric potential and the decrease of bandgap of NBTO micron crystal due to strain induced by ultrasonic vibration. A new fundamental mechanism for the improved degradation of organic dye has been proposed for piezoelectric and photoexcitation coupling. This work extends the application of wide band gap piezoelectric materials in the visible light area.
RESUMEN
Submicron Bi2Fe4O9 crystals were successfully synthesized by a one-step hydrothermal synthesis method and employed effectively as a visible-light-driven photocatalyst for the degradation of methylene blue dye. Scanning electron microscopy and transmission electron microscopy observations revealed that the as-prepared sample consisted mainly of submicron plates and a small quantity of submicron particles. The ultraviolet-visible absorption spectrum of the submicron Bi2Fe4O9 crystals shows two broad absorption edges in the visible region with band gaps of 1.57 and 2.15 eV, respectively. The photodegradation rate of Bi2Fe4O9 is more than twice that of TiO2 for the degradation of methylene blue under visible-light irradiation, demonstrating the excellent photocatalytic activity of these submicron Bi2Fe4O9 crystals. The acquired photocurrent densities are 43.3 and 46.6 µA/cm² for visible-light and ultraviolet-visible irradiation, respectively. These results demonstrate that the submicron Bi2Fe4O9 crystals are potential visible-light photocatalysts for use in environmental purification and solar energy utilization.
RESUMEN
LiNi1/3ZnxCo1/3-xMn1/3O2 (0.000 ≤ x ≤ 0.133) hollow microspheres are synthesized using MnO2 hollow microspheres both as a self-template and Mn source. These hollow microspheres, ~4 µm in diameter, are composed of approximately 300 nm basic nanoparticles. The XRD patterns of LiNi1/3ZnxCo1/3-xMn1/3O2 were analyzed by the RIETAN-FP program, and the obtained samples have a layered α-NaFeO2 structure. Electrochemical performances of the samples were carried out between 2.5 V and 4.5 V. The behavior of the lattice parameters is consistent with Cycling performance and rate performance change with increase of x. Compared with the others, the sample of x = 0.133 exhibits a relatively superior electrochemical performance. The specific capacity of x = 0.133 was increased by 10.7% than no-doped. In addition, the cyclic voltammograms curves of the second cycle show no significant alteration compared with the first cycle and the electrochemical impedance of zinc doping sample showed smaller transfer resistance than the no-doping sample.