Chromium (Cr) doped cobalt ferrite (Co1−xCrxFe2O4:x = 0.0, 0.02, 0.04, 0.06, 0.08, 0.1, denoted as to CCFO) hollow nanotubes were synthesized by electrospinnig method followed by, calcining treatment at 700 °C in air. The samples exhibited a single phase cubic spinel phase. The lattice constant of the samples was found to initially decreased and thereafter increases with increased of Cr content. The morphology analysis indicated that the samples displayed a disordered arrangements of hollow structures and the relevant surfaces were rough and porous. Transmission electron microscopy (TEM) paragraph confirmed that the doped CCFO nanotubes had a polycrystalline nature and exhibited the changes in the corresponding crystal structure. X-ray photoelectron spectroscopy (XPS) confirmed that Cr doping affect the crystal structure and atomic-binding energy. The analysis of magnetic hysteresis loop indicated an obvious reduction in the saturation magnetization (Ms) of cobalt ferrite with increasing in Cr substitution. The remanent magnetization (Mr) and coercivity were increased at first and then decreased with increasing of Cr content, which was elucidated by the surface effect and magnetic moment direction. The switching field distribution analysis indicated the magnetically crystal soft phase and there were multiple-step processes to reach magnetic reversal.
The effects of transition metal (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) doping on the stability, electronic structure and optical properties of β-Ga2O3 have been studied using GGA and GGA + U. The results show that the U value can correct the strong interaction of the d-layer, causing orbital hybridization and affecting the position and number of impurity energy levels. It can move the conduction band to higher energy levels and weaken the role of Ga-3p in the valence band. The Ti-doped β-Ga2O3 is easily formed, followed by V, Cr, Sc, Fe, Mn, Co, Ni, Cu, and Zn doping. Some bands change regularly with the increase of atomic number. All systems become degraded semiconductors after doping. All doping will make the β-Ga2O3 red shift. Among them, the absorption intensity of Cu doping in the visible light range is significantly improved.
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