Li Pengwei,Li Jie,Wang Yonglun,Yao Kai,Shan Shuo,Suo Xing,Ma Saisai
Praseodymium (Pr)–aluminum (Al)-co-doped M-type barium ferrite with Ba 0.85 Pr 0.15 Fe 12-x Al x O 19 ( x = 0.0–1.0) was prepared by combining solid-phase sintering with high-energy ball milling. The samples were characterized using a thermogravimetric analyzer, X-ray diffractometer, field emission scanning electron microscopy, Fourier transform infrared spectroscopy, and vibrating sample magnetometer. Thermogravimetric analysis indicated that M-type barium ferrite was formed at 1250 °C. X-ray diffraction patterns showed that Al doping did not destroy the crystal structure of barium ferrite. Field emission scanning electron microscopy showed that the samples had a hexagonal crystal structure. The wave numbers of Fourier transform infrared spectroscopy in the 597–607 and 452–459 cm −1 bands represent tetrahedral and octahedral clusters, respectively. With the increase in the amount of Al doping ( x ) from 0.0 to 1.0, the saturation magnetization ( M s ) and residual magnetization ( M r ) decreased continuously, and the magnetic anisotropy field ( H a ) and coercivity ( H c ) increased significantly.
Yang Yu,Li-Dong Wang,Wei-Li Li,Yu-Long Qiao,Yu Zhao,Yu Feng,Tian-Dong Zhang,Rui-Xuan Song,Wei-Dong Fei
Conventional ferroelectric oxides are of generally non-centrosymmetric crystals resulting from paraelectric-ferroelectric transitions. Here, we present a new donor-acceptor ion co-doping route to room-temperature ferroelectricity in rutile TiO 2 , where ionic pair of co-doping ions plays very important roles in generating local broken symmetry and polarization. The (Nb + Al) co-doped TiO 2 sintered with a two-step method exhibits ferroelectricity and piezoelectric response, and it is believed that Nb 5+ -Al 3+ pairs along TiO 2 [001] direction play important role in the ferroelectricity. A large lattice distortion can be induced in the vicinity of the ionic pair, which results in local broken-symmetry. The relative displacements of cations and anions around the ionic pair, induced by the lattice distortion, cause the local polarization. The results and mechanisms presented in this work provide a new approach to the design of new ferroelectrics via doping engineering.
The nickel-rich layered cathode material LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) has high energy density , lower cost and is a promising cathode material currently under development. However, its electrochemical and structural stability is poor during cycling. Among the many modification methods, cation doping has been consistently proven to be an effective strategy for enhancing electrochemical performance . Herein, the NCM811 cathode material was modified by solid-phase reactions with Mg and Al doped. In addition, the corresponding mechanism of NCM811 cathode material-doped modification is explored by density functional theory (DFT) calculations, and we have extended this approach to other ternary cathode materials with different ratios and obtained universal laws. Combined with DFT calculations, the results show that Mg 2+ occupies the Li + site and reduces the degree of Li + /Ni 2+ mixture; Al 3+ acts as a structural support during charging and discharging to prevent structural collapse. The electrochemical properties were tested by an electrochemical workstation and the LAND system, and the results showed that the capacity retention rate increased to varying degrees from 63.66% to 69.87% and 89.05% for NCM811-Mg and NCM811-Al at room temperature after 300 cycles, respectively. This study provides a theoretical basis and design strategy for commercializing cationic-doped modification of nickel-rich cathode materials.
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