Xingxing Yang

In this study LiFePO₄/C composite particles were synthesized using five different carbon sources via a one-step sol-gel method. La-doped LiFePO₄ was also synthesized using the sol-gel method. The XRD pattern of Li_xLa_yFePO₄ (x = 0.9~1.0, y = 0~0.1) after being calcined at 700 °C for 10 h indicates that as the doping ratio increased, the sample’s cell volume first increased then decreased, reaching a maximum value of 293.36 ų (x = 0.94, y = 0.06). The XRD patterns of Li_0.92La_0.08FePO₄ after being calcined at different temperatures for 10 h indicate that with increasing calcination temperature, the (311) diffraction peak drifted toward a smaller diffraction angle. Similarly, the XRD patterns of Li_0.92La_0.08FePO₄ after being calcined at 700 °C for different durations indicate that with increasing calcination times, the (311) diffraction peak drifted toward a larger diffraction angle. The infrared spectrum pattern of Li_xLa_yFePO₄ (x = 0.9~1.0, y = 0~0.1) after being calcined at 700 °C for 10 h shows absorption peaks corresponding to the vibrations of the Li–O bond and PO₄^3- group. An SEM analysis of Li_xLa_yFePO₄ (x = 1, y = 0; x = 0.96, y = 0.04; x = 0.92, y = 0.08) after being calcined at 700 °C for 10 h indicates that the particles were irregular in shape and of uniform size. The hysteresis loops of Li_0.92La_0.08FePO₄ after being calcined at 600 °C, 700 °C, or 800 °C for 10 h indicate that with increasing calcination temperature, the Ms gradually increased, while the Mr and Hc decreased, with minimum values of 0.08 emu/g and 58.21 Oe, respectively. The Mössbauer spectra of Li_xLa_yFePO₄ (x = 1, y = 0; x = 0.96, y = 0.04; x = 0.92, y = 0.08) after being calcined at 700 °C for 10 h indicate that all samples contained Doublet(1) and Doublet(2) peaks, dominated by Fe²⁺ compounds. The proportions of Fe²⁺ were 85.5% (x = 1, y = 0), 89.9% (x = 0.96, y = 0.04), and 96.0% (x = 0.92, y = 0.08). The maximum IS and QS of Doublet(1) for the three samples were 1.224 mm/s and 2.956 mm/s, respectively.

Magnetic Functional Nanomaterials Co_1−yZn_yRE_xFe_2−xO₄ (RE (rare-earth) = La,Sm,Gd) were prepared using the sol–gel combustion method. XRD characterization confirms that the ferrite samples we synthesized are single-phase cubic structures. The variation in the average crystalline size and lattice parameter is related to RE ion doping. The Mössbauer spectra of CoRE_xFe_2−xO₄ are two sets of magnetic six-wire peaks that indicate the ferrimagnetic behavior of the sample. The calcination temperature greatly influences the absorption area of Mössbauer for CoFe₂O₄, indicating that the calcination temperature affects the iron ion content at the octahedral B and tetrahedral A sites. Additionally, scanning electron microscopy measurements of the substituted specimens reveal that the ferrite powders are nanoparticles. With an increase in RE ions, the coercivity increases, and the saturation magnetization changes obviously. The XRD characterization of Co_0.7Zn_0.3La_xFe_2−xO₄ shows that the main crystalline phase of the sample is the cubic spinel structure phase, and there are fewer secondary crystalline phases. The lattice parameter tends to decrease with the substitution of La³⁺ ions. The average grain size decreased significantly with the increase in La content. From ferrimagnetic state transition to relaxation behavior, the hyperfine magnetic field decreases in La concentration by room temperature Mössbauer spectra. With the substitution of La³⁺ ions, both the saturation magnetization and coercivity of the samples were reduced, and the coercivity of all samples was lower.

Cd_xNi_0.5−xCu_0.2Zn_0.3Fe₂O₄ (0 ≤ x ≤ 0.50) ferrite with a spinel structure was prepared using the sol–gel self-propagation method. The effects of Cd²⁺ doping on the structure, morphology, dielectric, and magnetic properties of Ni–Cu–Zn ferrite were examined using XRD, SEM, EDX, FTIR, MPMS, and dielectric tests. The cubic spinel structure was verified by XRD and FTIR analyses. The crystallite size and particle size information of the samples were obtained with XRD and SEM analysis. The sample particle size belonged to a class of nanoscale materials with a particle size range of 1–100 nm. The minor difference between the grain size and particle size indicated that the sample nanoparticles were composed of numerous microcrystals. The EDX spectra indicated that the samples contained all stoichiometric elements. MPMS was used to measure the hysteresis lines of the samples. According to the hysteresis line, the saturation magnetization intensity (M_s), coercivity (H_c), and magnetic moment (μ_B) of the sample increased and then decreased with the increase in cadmium concentration. The magnetization strength (M_s) is between 4–67 emu/g, and the coercivity (H_c) is between 9–46 Oe. The curves of the real part of the dielectric constant (ε′), the imaginary part of the dielectric constant (ε″), and the loss factor (tanδ) with frequency were measured in the frequency range 100 Hz–100 kHz by means of an impedance analyzer. The complex modulus spectrum was analyzed to understand the dynamics of the conduction process.

Perovskite is the largest mineral on earth and has a variety of excellent physical and chemical properties. La_1−xR_xFeO₃ (R = Co, Al, Nd, Sm) were synthesized using the sol-gel method and analyzed by XRD, TG-DTA, and VSM. With the increase in the Co²⁺ doping content, the diffraction peak drifted in the direction of a larger angle. The grain size of La_1−xR_xFeO₃(R = Co) is mainly concentrated between 50.7 and 133.5 nm. As the concentration of Co²⁺ increased, the magnetic loop area and magnetization increased. La_1−xR_xFeO₃(R = Al) is an orthorhombic perovskite structure, the grain size decreased with the increase in Al³⁺ doping concentration, and the minimum crystallite is 17.9 nm. The magnetic loop area and magnetization increased with the increase in Al³⁺ ion concentration. The enclosed area of the M-H curve of the sample decreased, and the ferromagnetic order gradually weakened and tended to be antiferromagnetic, which may be due to the increase in sintering temperature, decrease in the iron oxide composition, and changes in the magnetic properties. Proper doping can improve the magnetization of La_1−xR_xFeO₃(R = Nd), refine the particles, and obtain better magnetic performance. As the Nd³⁺ ion concentration increased, the magnetic properties of the samples increased. Ms of La_0.85Co_0.15FeO₃ prepared by different calcination time increases with the increase in calcination time. As the Sm³⁺ ion concentration increased, the magnetic properties of the samples increased. Proper doping can improve the magnetization of La_1−xR_xFeO₃(R = Sm), refine the particles, and generate better magnetic performance.