Search

In this work, Nd (0.5, 1.0, 1.5, and 2.0 at%)-doped TiO2 thin films were synthesized on Si (100) substrates using a sol–gel spin-coating technique. The formation of the anatase phase was demonstrated by X-ray diffraction and Raman spectroscopy. It was also demonstrated that the doping of the Nd element resulted in a TiO2 crystal structure. X-ray photoelectron spectroscopy proved that the doping of Nd element promoted the transfer of Ti4+ to Ti3+, which facilitates the photocatalytic performance of the TiO2 films. Scanning electron microscope and atomic force microscope demonstrated that all of the Nd-doped film surfaces showed different degrees of aggregation relative to the pure TiO2 film surface. It was verified that the doping of Nd altered the lattice structure of TiO2 thin films, resulting in lattice defects on the surface and changing the grain size of the films. Meanwhile, the lattice defects and changes in the chemical state affect the photocatalytic performance of TiO2 films, and the highest photoactivity was observed for an Nd doping concentration of 1.0 at%. Nd doping causes lattice defects conducive to the formation of more Ti3+ oxidation centers and reduces the photogenerated electron–hole recombination rate, resulting in the improved photocatalytic performance of TiO2 films.

TiO2 thin films were prepared by sol-gel spin-coating (SGSC) and electron beam-physical vapor deposition (EB-PVD) methods and annealed at different temperatures (Ta). X-ray diffraction spectroscopy (XRD) results show that the TiO2 films prepared by the SGSC method transformed from the anatase single phase to the coexistence of anatase and rutile with the increase of Ta. However, TiO2 films prepared by the EB-PVD method existed only in the anatase phase, and the crystalline strength was enhanced with the increase of Ta. Meanwhile, particles of TiO2 targets annealed at different Ta showed a rutile phase for TiO2 target particles in the EB-PVD method. The results indicate that the EB-PVD method hinders the nucleation growth and phase transformation of TiO2 films. Scanning electron microscopy and atomic force microscopy also show that the grain size and R ms of TiO2 thin films prepared by the SGSC method increased with the increase of Ta, and the grain size becomes inhomogeneous when the rutile phase is formed. Ultraviolet–visible results show that the forbidden bandwidth and light absorption capacity increase with increasing Ta. For the EB-PVD method, the grain size and surface roughness gradually increased when the Ta of the films was less than 800 °C, while annealing at 800 °C changed the direction of growth and nucleation, and also produced surface cracks; XRD verified the hypothesis that the EB-PVD method hinders the nucleation growth as well as the phase transition of the films. Weak differences in the optical absorption properties and bandgap values of the films also indicate that the EB-PVD method hinders the phase transformation of TiO2 films. Finally, the results of degradation of methylene blue (MB) under simulated visible light showed that the films prepared by the SGSC method gradually improved the photocatalytic performance with the enhancement of the crystalline strength of the anatase phase. The TiO2 films prepared by the EB-PVD method improved the photocatalytic performance with the increase of the active area. [ABSTRACT FROM AUTHOR]

Multiferroic Bi1-x Gd x FeO3 (0≤x≤0.15) samples were prepared using the solid-state reaction method. The influence of Gd substitution on the crystal, the electronic structure, and the magnetic properties of Bi1-x Gd x FeO3 was studied. X-ray diffraction spectra show that Gd substitution changes the crystal structure of the Bi1-x Gd x FeO3 system from a rhombohedral to an orthorhombic phase. According to Fe L-edge X-ray absorption spectra (XAS), Fe ions are found to be formally trivalent for any value of x in Bi1-x Gd x FeO3. Based on a careful examination of Fe L and O K-edge XAS spectra, it was found that the enhanced magnetization which results from increasing Gd content is attributed to a reduced degree of hybridization between Fe 3d-O 2p orbitals. The crystal and electronic structures exhibit a causal relationship between themselves and demonstrated intrinsic mutual dependence in their corresponding variations. [ABSTRACT FROM AUTHOR]

The structural and magnetic characterization of pure and N-doped TiO2 nanowires prepared by hydrothermal method was reported. The X-ray absorption near edge structure and X-ray powder diffraction measurements show that N was doped into TiO2 host after annealing in NH3. It is found that doping with N has no effect on the anatase structure of TiO2 nanowires and N related secondary phase is not formed. Magnetization studies reveal that the doped and undoped TiO2 exhibited room temperature ferromagnetism and that saturation magnetization increased with N-doping. Thus, the results indicate the oxygen vacancies and crystallinity play a crucial role in room temperature ferromagnetism of TiO2 nanowires. [ABSTRACT FROM AUTHOR]

The chalcopyrite structure is a rich source for the exploration of new IR materials. However, not all of the compounds with a chalcopyrite-type structure exhibit satisfactory optical properties, which may originate from their different microstructure features. In this work, we selected four classical chalcopyrite materials, A I GaS 2 (A I = Ag, Cu) with normal structures and A II Ga 2 S 4 (A II = Zn, Hg) with defect structures, to study their electronic structures, optical properties including the contribution of ions and ion groups to their band gaps, SHG responses and birefringences by the first-principles method. The results uncover that the different band gaps are mainly caused by the d orbitals of A* (A* = A I , A II )-site atoms and dp hybridizations between the A*-site and S atoms. In addition, the more powerful covalent bonds of A II -S and Ga-S in the A II Ga 2 S 4 lead to the larger SHG responses of ZnGa 2 S 4 and HgGa 2 S 4 . For the birefringences, the sizes of the A*-site atoms make sense, namely larger size will lead to higher distortion of tetrahedra, then result in large birefringences. All the above analyses conclude that the A*-site atoms in the chalcopyrite structures play a modulation role in determining the optical properties., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)