Yun He

Olivine-type LiFePO₄ is a promising cathode candidate for lithium-ion batteries. In this study, undoped and a series of Co-substituted Li_xCoᵧFePO₄ (x = 0.85–1.00, y = 0–0.15) nanocomposites were synthesised by sol–gel auto-combustion using organic–inorganic hybrid xerogel precursors. The effects of sol pH, calcination temperature, calcination holding time and Co²⁺-doping content on crystal structure, phase composition, crystallinity, particle morphology, magnetic-hysteresis performance and Fe valence-state distribution were systematically explored using TG-DTA, XRD, FT-IR, SEM, VSM and Mössbauer spectroscopy. XRD analyses reveal that intermediate-pH conditions (pH 6.5–7.5) readily produce crystalline impurities including LiFeO₂ and Fe₂O₃, whereas high-pH environments (pH 8.5–9.5) facilitate the formation of pure-phase olivine-structured products. Diffraction-peak sharpness increases with rising calcination temperature, indicating improved crystallinity, and the samples treated at 800 °C exhibit the sharpest diffraction signals. As the doping level increases, the (311) diffraction peak first shifts toward lower and then higher angles; correspondingly, the unit-cell volume first increases to a maximum and then declines, whereas the crystallite size varies non-monotonically, confirming that Co doping predominantly modifies the lattice geometry. For the heavily doped Li_0.85Co_0.15FePO₄, carbothermal reduction induced by excessive thermal treatment (T > 700 °C or extended holding) yields a secondary phosphide phase that is tentatively indexed as Co₂P from two weak reflections. Within the Co-substituted series, the 700 °C—10 h condition gives a single-phase product with the highest saturation magnetisation (Ms = 3.45 emu·g⁻¹), which decreases to 2.07 emu·g⁻¹ at 800 °C. VSM results demonstrate a decoupling between the saturation magnetisation (Ms) and the coercivity (Hc); the weak ferromagnetic hysteresis observed in all samples signals trace ferromagnetic secondary phases—most plausibly amorphous or nanoscale products of xerogel thermal decomposition that lie below the XRD detection limit—rather than indicating phase purity; this attribution is indirect and is critically assessed below. Mössbauer spectroscopy validates the coexistence of dominant high-spin Fe²⁺ and minor Fe³⁺ species within the samples. High-level Co substitution (y = 0.15) lowers the relative proportion of the Fe³⁺ impurity species to 7.2% and alters the local Fe coordination environments without generating magnetically ordered sextet components. This work demonstrates that the sol–gel-derived hybrid xerogel is a tunable platform for fabricating phosphate-based battery nanocomposites and provides insights for the gel-precursor-directed design of energy-storage functional materials.

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.

A_yB_1−yC_xFe_2−xO₄ (C=Ho,Gd,Al) ferrite powders have been synthesized by the sol-gel combustion route. The X-ray diffraction of the CoHo_xFe_2−xO₄ (x = 0~0.08) results indicated the compositions of single-phase cubic ferrites. The saturation magnetisation of CoHo_xFe_2−xO₄ decreased by the Ho³⁺ ions, and the coercivity increased initially and then decreased with the increase of the calcination temperature. The Mössbauer spectra indicated that CoHo_xFe_2−xO₄ displays a ferrimagnetic behaviour with two normal split Zeeman sextets. The magnetic hyperfine field tends to decrease by Ho³⁺ substitution owing to the decrease of the A–B super-exchange by the paramagnetic rare earth Ho³⁺ ions. The value of the quadrupole shift was very small in the CoHo_xFe_2−xO₄ specimens, indicating that the symmetry of the electric field around the nucleus is good in the cobalt ferrites. The absorption area of the Mössbauer spectra changed with increasing Ho³⁺ substitution, indicating that the substitution influences the fraction of iron ions at tetrahedral A and octahedral B sites. The X-ray diffraction of Mg_0.5Zn_0.5C_xFe_2−xO₄(C=Gd,Al) results confirmed the compositions of single-phase cubic ferrites. The variation of the average crystalline size and lattice constant are related to the doping of gadolinium ions and aluminum ions. With increasing gadolinium ions and aluminum ions, the coercivity increased and the saturation magnetization underwent a significant change. The saturation magnetization of AlMg_0.5Zn_0.5FeO₄ ferrite reached a minimum value (M_S= 1.94 mu/g). The sample exhibited ferrimagnetic and paramagnetic character with the replacement with Gd³⁺ ions, that sample exhibited paramagnetic character with the replacement with Al³⁺ ions, and the isomer shift values indicated that iron is in the form of Fe³⁺ ions.

LiFePO₄ takes advantage of structure stability, safety and environmental friendliness, and has been favored by the majority of scientific researchers. In order to further improve the properties of LiFePO₄, AO-type metal oxides (MgO and ZnO) and LiFePO₄/C composites were successfully prepared by a two-step sol-gel method. The effects of AO-type metal oxides (MgO and ZnO) on LiFePO₄/C composites were studied. TG, XRD, FTIR, SEM and VSM analysis showed that the final product of the MgO and LiFePO₄/C composite was about 70.5% of the total mass of the precursor; the complete main diffraction peak of LiFePO₄ and MgO can be found without obvious impurity at the diffraction peak; there is good micro granularity and dispersion; the particle size is mainly 300 nm; the saturation magnetization (Ms), the residual magnetization (Mr) and the area of hysteresis loop are increased with the increase in MgO content; and the maximum Ms is 11.11 emu/g. The final product of ZnO and LiFePO₄/C composites is about 69% of the total mass of precursors; the complete main diffraction peak of LiFePO₄ and ZnO can be found without obvious impurity at the diffraction peak; there is good micro granularity and dispersion; the particle size is mainly 400 nm; and the coercivity (Hc) first slightly increases and then gradually decreases with the increase of zinc oxide.

A new system for preparing ¹⁴C samples was established for a compact accelerator mass spectrometer (GXNU-AMS) at Guangxi Normal University. This sample preparation system consists of three units: a vacuum maintenance unit, a CO₂ purification unit, and a CO₂ reduction unit, all of which were made of quartz glass. A series of radiocarbon (¹⁴C) preparation experiments were conducted to verify the reliability of the system. The recovery rate of graphite obtained was more than 80%. The carbon content in the commercial toner and wood sample was linearly fitted to the CO₂ pressure in the measurement unit of the system. The results showed a good linear relationship, indicating that the reliability of the sample preparation system. AMS measurements were conducted on a batch of standard, wood, and dead graphite samples prepared using this system. The results showed that the beam current of ¹²C- for each sample was more than 40 μA, the carbon contamination introduced during the sample preparation process was ∼ 2 × 10^–15, and that the new sample preparation system is compact, low-contamination, and efficient and meets the GXNU-AMS requirements for ¹⁴C samples.

Many waterflooding oil fields, injecting water into an oil-bearing reservoir for pressure maintenance, are in their middle to late stages of development. To explore the geological conditions and improve oilfield recovery of the most important well group of the Hu 136 block, located on the border areas of three provinces (Henan, Shandong, and Hebei), Zhongyuan Oilfield, Sinopec, central China, a ¹⁴C cross-well tracer monitoring technology was developed and applied in monitoring the development status and recognize the heterogeneity of oil reservoirs. The tracer response in the production well was tracked, and the water drive speed, swept volume of the injection fluid were obtained. Finally, the reservoir heterogeneity characteristics, such as the dilution coefficient, porosity, permeability, and average pore-throat radius, were fitted according to the mathematical model of the heterogeneous multi-layer inter-well theory. The ¹⁴C-AMS technique developed in this work is expected to be a potential analytical method for evaluating underground reservoir characteristics and providing crucial scientific guidance for the mid to late oil field recovery process.

Water loss of the gel polymer electrolytes (GPEs) and dendrites growth on Zn anode are overriding obstacles to applying flexible zinc‐air batteries (ZABs) for wearable electronic devices. Nearly all previous efforts aim at developing novel GPEs with enhanced water retention and therefore elongate their lifespan. Herein, a facile interface engineering strategy is proposed to retard the water loss of GPE from the half‐open structured air cathode. In detail, the poly(ethylene vinyl acetate)/carbon powder (PEVA‐C) nanofiber composite interface layer with features of hydrophobicity, high conductivity, air permeability, and flexibility are prepared on the carbon cloth and set up between the GPE and electrode. The as‐assembled ZAB with simple alkaline PVA GPE exhibits an impressive cycle life of 230 h, which outperforms ZAB without the PEVA‐C nanofibers interface layer by 14 times. Additionally, the growth of Zn dendrites can be suppressed due to the tardy water loss of GPE.