Measurements Of Magnetic Properties Research Articles

Temperature influence on NiFeMo nanoparticles magnetic properties and their viability in biomedical applications.

NiFeMo alloy nanoparticles were synthesized by co-precipitation in the presence of organic additives. Nanoparticles thermal evolution shows that there is a significant increase in the average size (from 28 to 60 nm), consolidating a crystalline structure of the same type as the Ni3 Fe phase but with lattice parameter a=0.362 nm. Measurements of magnetic properties follow this morphological and structural evolution increasing saturation magnetization (Ms) by 578% and reducing remanence magnetization (Mr) by 29%. Cell viability assays on as-synthesized revealed that nanoparticles (NPs) are not cytotoxic up to a concentration of 0.4μg/mL for both non-tumorigenic (fibroblasts and macrophages) and tumor cells (melanoma).

Magnetic property measurement and analysis of high-frequency soft magnetic materials under non-sinusoidal excitation considering temperature effect

Electrical equipment operates under various temperatures and non-sinusoidal excitation, which makes magnetic properties of soft magnetic materials quite different from those under room temperature and sinusoidal excitation. Magnetic properties and loss characteristics of the ferrite (N87) and nanocrystalline alloy (FT-3KL) are measured and analyzed in the range of 25 °C to 125 °C from 5 kHz to 20 kHz under both square and rectangular excitation with different duty ratios. The temperature dependence of these materials under different conditions is systematically compared with normalization method. The comprehensive performance of core materials is discussed in combination with the experimental phenomena and results.

Measurement of magnetic properties of grain-oriented electrical steel under bending stress in a wide frequency range

To clarify the mechanism of the magnetic properties deterioration and the increasing loss of the Grain-Oriented (GO) electrical steel wound cores under serving conditions, the effect of the bending stress in a wide frequency range should be thoroughly investigated. In this paper, a magnetic properties measuring system for GO electrical steel under different bending stress from 50 Hz to 1000 Hz is proposed. To ensure the accuracy and reproductivity of the measurements, the waveform of magnetic flux densities should be controlled to be sinusoidal. However, the bending stress aggravates the material’s nonlinear properties, making waveform control very difficult. To solve this problem, a frequency-domain adaptive dual-loop feedback control algorithm is developed. Obtained results show that the proposed method has a good effect on waveform control under bending stress, and the loss of the material under different magnetizing conditions is then analyzed.

Impact of manganese diffusion into non-oriented electrical steel on power loss and permeability at different temperatures

Minimising power losses and their consequences is a significant matter in electrical steel applications. Increasing the resistivity of the steel strips has been confirmed as a successful method to overcome the problem of power losses. To increase the resistivity of the strip, different effective methods have been proposed and tested. In this work, a new material has been proposed to achieve the objective of increasing the resistivity of the steel samples by adding Manganese (IV) oxide based on a diffusion technique. The surface of the samples is to be coated with the proposed Manganese oxide. This should guarantee an increase in the resistivity of the samples, which in turn reduces the power losses caused by the eddy current. The samples tested were of non-oriented electrical steels containing 2.4 wt% Si-Fe (with a thickness of 0.305 mm*300 mm*30 mm). It was measured for losses and permeability before and after treatment by a Single Strip Tester (SST) at 0.5–1.7 T using an Alternating Current magnetic properties measurement system under controlled sinusoidal at different frequencies. The obtained results revealed that the depth of Manganese oxide diffusion is inversely proportional to the increase in the temperature. It was demonstrated that the best amount of diffusion of the element into the strips was achieved at 525°C, which was 60 weight % in comparison with 700°C which was 20 wt%. Likewise, at 800°C it was 7 wt%. However, the depth of diffusion of the manganese was the same at those tested temperatures, which were equal to 200 µm deep on each of the side strips. The diffusion of the material was investigated using Scanning Electron Microscope (SEM) coupled with Energy Dispersive X-ray Spectroscopy (EDS). Furthermore, from the results, it was concluded that the power losses in the coating samples were improved by 9% as compared with uncoated samples.

Efficient peroxymonosulfate activation by magnetic CoFe2O4 nanoparticle immobilized on biochar toward sulfamethoxazole degradation: Performance, mechanism and pathway

Utilizing biomass waste to create highly efficient biochar-based catalysts has drawn intensively interest since it adheres to the idea of waste recycling in environmental conservation. Herein, CoFe2O4 nanoparticles immobilized on biochar (BC) derived from rape straw were synthesized and applied in degrading sulfamethoxazole (SMX) by activating peroxymonosulfate (PMS). Experimental results indicated that the 30 wt% CoFe2O4/BC composite catalyst had the best catalytic activity with the SMX degradation efficiency of 93% within 20 min, which was probably the fact that BC as a carrier not only effectively inhibited the agglomeration of CoFe2O4 nanoparticles and increased the active sites, but also could simultaneously participate in the catalytic degradation reaction as an activator of PMS. In addition, cycle experiments illustrated that the as-prepared catalyst possessed the excellent stability, and the magnetic property measurements implied that they were convenient for separation and recovery. According to quenching experiments, electron paramagnetic resonance (EPR) and electrochemical studies, both radical and non-radical process participated into degrading SMX, where the generated SO4·-, ·OH and O2·- as the major radical active species while 1O2 and direct electron transfer were responsible for the non-radical route. Besides, using high-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis, a potential SMX degradation pathway was suggested. The present CoFe2O4/BC composite would be a promising PMS activation catalyst for environmental remediation.

Anomalous Hall effect in Pt/La<sub>0.67</sub>Sr<sub>0.33</sub>MnO<sub>3</sub> heterojunctions

Many emergent and novel phenomena occur in nonmagnetic/ferromagnet heterostructures. In particular, Pt/ferromagnet heterostructures where the Pt has strong spin-orbit coupling and thus can convert spin current into charge current, has attracted a great attention recently. The anomalous Hall effect (AHE) has been found in many Pt/ferromagnet heterostructures. However, the underlying physics remains elusive, so it is necessary to find more heterostructures in order to provide more experimental data. In this work, we investigate anomalous Hall resistances (AHRs) in Pt thin films sputtered on epitaxial La<sub>0.67</sub>Sr<sub>0.33</sub>MnO<sub>3</sub> (LSMO) ferromagnetic films. High-quality Pt/LSMO heterojunctions are fabricated by pulsed laser deposition and RF-magnetron sputtering. The physical properties of LSMO films are characterized by the measurements of magnetic and transport properties. The AHR mainly contributed by Pt in the Pt/LSMO heterojunction increases sharply with temperature decreasing and changes its sign below 40 K. Furthermore, the AHR decreases sharply with the increase of Pt thickness. Those facts suggest that the ferromagnetism of Pt originates from interface due to magnetic proximity effect. Interestingly, this heterojunction can exhibit possible signal of topological Hall effect under low applied magnetic field. The above results provide an experimental basis for further understanding the interactions between electron spin and charge transport in nonmagnetic/ferromagnetic heterostructures.

Structure and Magnetic Properties of SrFe12−xInxO19 Compounds for Magnetic Hyperthermia Applications

In this work, complex studies of the structure and magnetic properties of SrFe12-xInxO19 powders obtained by the mechanochemical and citrate methods were carried out. The solubility of In in strontium hexaferrite SrFe₁₂O₁₉ at 1200 °C was determined. The structure and properties of the powders were studied using X-ray diffraction analysis, Mössbauer spectroscopy and scanning electron microscopy. Measurements of magnetic properties in magnetic fields up to 1600 kA/m were also performed. Additionally, the hyperthermia effect was investigated. The possibility of controlling the coercivity of the samples in the range from 188.9 kA/m to 22.3 kA/m and saturation magnetization from 63.5 A·m2/kg to 44.2 A·m2/kg with an increase in the degree of In doping was also demonstrated. Investigation of the magnetic hyperthermia of the samples was carried out by temperature measurement with an IR camera when they were introduced into alternating magnetic fields of various frequencies (144, 261 and 508 kHz) and amplitudes (between 11.96 and 19.94 kA/m). According to the study result, there was detected the heating of the SrFe12-xInxO19 sample (x = 1.7). The highest values of magnetic hyperthermia of the sample were observed in a 19.94 kA/m magnetic field and a frequency of 261 kHz. At a concentration of 56.67 g/L, the sample was heated from 23 to 41 °C within 2 min. The parameters SLP (specific loss power) and ILP (intrinsic loss power) were calculated.

Magnetic structure and spin dynamics of the quasi-two-dimensional antiferromagnet Zn-doped copper pyrovanadate

Magnetic properties of the antiferromagnet Zn$_{0.15}$Cu$_{1.85}$V$_2$O$_7$ (ZnCVO) have been thoroughly investigated on powder and single-crystal samples. The crystal structure determination using powder x-ray and neutron diffraction confirms that ZnCVO with Zn = 0.15 is isostructural with $\beta$-Cu$_{2}$V$_2$O$_7$ ($\beta$-CVO) with small deviation in the lattice parameters. Macroscopic magnetic properties measurements also confirm the similarity between the two compounds. The Cu$^{2+}$ spins were found to align along the crystallographic $c$-axis, antiparallel to their nearest neighbors connected by the leading exchange interaction $J_1$. Spin dynamics reveals a typical symmetric spin-wave dispersion with strong interactions in the $bc$-plane and weak interplane coupling. The exchange interaction analysis indicates that the spin network of ZnCVO is topologically consistent with the previous DFT prediction but the values of leading exchange interactions are contradictory. Furthermore, rather than the predicted 2D honeycomb structure, the spin network in ZnCVO could be better described by the anisotropic 2D spin network composing of $J_1$, $J_5$, and $J_6$ interactions, four bonds per one spin site, coupled by weak interplane interactions.

High-Pressure Synthesis and Magnetic and Electrical Properties of Fe-Doped Bi3Re3O11 and Bi3Os3O11

Under high-pressure and high-temperature conditions, doped Bi3Re3O11 and Bi3Os3O11 with Fe up to 29 atomic % were synthesized. The crystal structures and chemical compositions of Bi3Os2.45Fe0.55O11 and Bi3Re2.13Fe0.87O11 were determined by synchrotron powder X-ray diffraction and electron probe microanalysis. Both crystal structures were explained by a KSbO3-type model with the space group Pn3̅. Magnetic and electronic transport property measurements showed that Bi3Os2.45Fe0.55O11 exhibited a ferrimagnetic transition at the highest magnetic ordering temperature of 490 K in the KSbO3-type, while Bi3Re2.13Fe0.87O11 exhibited a spin glassy behavior below 22 K. The magnetoresistance at 5 K and 90 kOe was almost zero for Bi3Os2.45Fe0.55O11, but -10% for Bi3Re2.13Fe0.87O11. These results suggest that KSbO3- type 5d oxides, which exhibit only weak temperature-dependent paramagnetism to date, are a group of compounds that can be converted into spintronic materials by doping with 3d elements, leading to the development of new KSbO3-type materials with both theoretical and practical significance.

Magnetic solid-phase extraction based on GO/Fe3O4 coupled with UPLC-MS/MS for determining nitroimidazoles and their metabolites in honey

A magnetic graphene oxide (GO/Fe3O4) nanocomposite was synthesized in one step by a chemical coprecipitation method, which was further used for magnetic solid-phase extraction (MSPE). This study aimed to combine GO/Fe3O4 with ultra-high-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) to detect the nitroimidazoles (NDZs) and their three major metabolites in honey samples. GO/Fe3O4 was characterized by transmission electron microscopy (TEM), Fourier transform-infrared (FT-IR) spectroscopy, and magnetic property measurement system (MPMS), and the influencing parameters such as adsorbent amount, pH of the dissolved sample solution, sample volume, type and volume of the eluent, shaking speed, and adsorption and desorption time were optimized. Under the optimized conditions, the limits of detection (LOD) and quantitation (LOQ) of the method were 0.003–0.08 μg kg−1 and 0.009–0.3 μg kg−1, respectively, with good linearity reported in the range of 0.5–20 μg kg−1 (R2 ≥ 0.9991). The average recoveries of 10 analytes were in the range of 66.0%–90.8% with relative standard deviations (RSD) lower than 6.9% (n = 6). The preparation of GO/Fe3O4 and the extraction process were convenient and rapid, and consumed small amounts of organic solvents. The optimized method was successfully applied for extracting NDZs and their three major metabolites from honey samples with good accuracy.

Co-precipitation synthesis of LaFe1-xAlxO3 (x = 0–0.2) on structure and electromagnetic properties

The synthesis of LaFe1-xAlxO3 (x = 0–0.2) on the structure and electromagnetic properties using the co-precipitation method were evaluated. LaFe1-xAlxO3 (x = 0–0.2) materials were synthesized using lanthanum chloride and natural iron sand powders. The mixing process of precursors was held with a hotplate temperature of 60 °C. The calcination process was done at 400 °C for 2 h. Then samples were analyzed using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Vibrating Sample Magnetometer (VSM), and CV meter. The XRD patterns result in two phases of LaFeO3 and Fe2O3. SEM images were performed that the powders are porous agglomerates. The particle size distribution is shown in the histogram that the samples are in the range of 50–500 nm, respectively. Then, the magnetic properties measurement of VSM analysis studied the substitution of Fe to Al ions decreases magnetic properties and BHmax in LaFe1-xAlxO3 (x = 0–0.2). The I-V measurements conducted the substitution of Fe to Al ions increase with a nonlinear reversal current in LaFeO3. These results show that LaFe1-xAlxO3 (x = 0–0.2) was recommended as the magnetic permanent material and perovskite material based on electromagnetic properties.

An optimized sono-heterogeneous Fenton degradation of olive-oil mill wastewater organic matter by new magnetic glutarlaldehyde-crosslinked developed cellulose.

The present study highlights the olive mill wastewater (OMW) treatment characteristics through a sono-heterogeneous Fenton process using new designed [GTA-(PDA-g-DAC) @Fe3O4] and characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), magnetic properties measurements, and point of zero charge (pH pzc) analysis. A preliminary removal study showed significant degradation efficiency (75%) occurred combining the magnetic synthesized catalyst [GTA-(PDA-g-DAC)@Fe3O4] ([catalyst] = 2 g/L) with US /H2O2 and maintaining 500WL-1 ultrasonic power (US). The values obtained by US only were (13%), H2O2/US (18%), US/Fe3O4 (28%), and US /Fe3O4/H2O2(35%). The catalytic findings have shown that [GTA-(PDA-g-DAC)@Fe3O4] exhibited good properties for OMW compound's degradation. The sonocatalytic process coupling and extra oxidant addition resulted in the degradation substantial levels. For instance, the concomitant effect of degradation optimized parameters; H2O2 10 mM, [GTA-(PDA-g-DAC) @Fe3O4] nanocomposites 2.5 g/L, at pH 3, and T 35 °C for 70 min resulted in an almost complete mineralization of aqueous OMW solution followed by a significant decolorization. Oxidation results exhibited efficient degradation rates in total phenolic compounds (TPC), total amino compounds (TAC), and chemical oxygen demand (COD) oxidation rate were 89.88, 92.75, and 95.66 respectively following the optimized sono-heterogeneous catalytic Fenton process. The prepared magnetic catalyst exhibited a good stability during repeated cycles. The gathered findings gave the evidence that sono-heterogeneous catalytic Fenton process is a promising treatment technology for OMW effluents.

Magnetocaloric properties of transition metal doped high entropy LaFe11Si2 alloys on Fe sites

The working temperature range of magnetic refrigeration (MR) is severely limited by the narrow range of magnetic entropy change (ΔSM) of magnetocaloric (MC) materials, which especially hinders MR applications near room temperature. Here, high-entropy La(Fe, Si)13 based MC materials with increasing number of equimolar transition metal elements such as Mn, Co, Ni, and Cr occupying Fe sites were synthesized using arc melting and annealing, to stabilize the La(Fe, Si)13 phase, and to increase δFWHM. Atomic resolution aberration corrected scanning transmission electron microscopy and elemental mapping confirmed that the doped transition metal elements uniformly occupy the Fe sites. Due to enhanced configuration entropy, the high entropy alloy has achieved La(Fe, Si)13 single phase structure. Magnetic property measurements reveal that the working temperature range of the high entropy alloy has increased by 141.3%. This work provides a new method to design novel MC materials for better stability and larger temperature range.

Comparison between machine linear regression (MLR) and support vector machine (SVM) as model generators for heavy metal assessment captured in biomonitors and road dust

Exposure to suspended particulate matter (PM), found in the air, is one of the most acute environmental problems that affect the health of modern society. Among the different airborne pollutants, heavy metals (HMs) are particularly relevant because they are bioaccumulated, impairing the functions of living beings. This study aimed to establish a method to predict heavy metal concentrations in leaves and road dust, through their magnetic properties measurements. For this purpose, machine learning, automatic linear regression (MLR), and support vector machine (SVM) were used to establish models for the prediction of airborne heavy metals based on leaves and road dust magnetic properties. Road dust samples and leaves of two common evergreen species (Cupressus lusitanica/Casuarina equisetifolia) were sampled simultaneously during two different years in the Great Metropolitan Area (GMA) of Costa Rica. MLR and SVM algorithms were used to establish the relationship between airborne heavy metal concentrations based on single (χlf) and multiple (χlf y χdf) leaf magnetic properties and road dust. Results showed that Fe, Cu, Cr, V, and Zn concentrations were well-simulated by SVM prediction models, with adjusted R2 values ≥ 0.7 in both training and test stages. By contrast, the concentrations of Pb and Ni were not well-simulated, with adjusted R2 values < 0.7 in both training and test stages. Heavy metal predicción models using magnetic properties of leaves from Casuarina equisetifolia, as collectors, yielded better prediction results than those based on the leaves of Cupressus lusitanica and road dust, showing relatively higher adjusted R2 values and lower errors (MAE and RMSE) in both training and test stages. SVM proved to be the best prediction model with variations between single (χlf) and multiple (χlf y χdf) magnetic properties depending on the element studied.

ZnII-DyIII single-molecule magnets constructed by salen-type ligand, acetate and β-diketonate

A series of ZnII-DyIII complexes with molecular formula [LZn(CH3COO)Dy(hfac)2] (1), [LZn(CH3COO)2Dy(dbm)]·CH2Cl2 (2), [LZn(CH3COO)Dy(btfa)2]·CH2Cl2 (3), (H2L = N,N'-bis(3-methoxysalicylidene)-1,2-phenylenediamine, hfac = hexafluoroacetylacetone, dbm = dibenzoylmethane, btfa = benzoyltrifluoride acetone) were structurally and magnetically characterized. They have similar ZnII-DyIII structural cores bridged by N and O atoms of the hexadentate salen type ligand (L). The main difference between them is the peripheral β-diketonate co-ligands surrounding DyIII ion. Dynamic magnetic properties measurements revealed that complexes 1-3 exhibit the field-induced SMM behavior with relaxation energy barriers Ueff/kB of 45.49 K, 69.28 K and 101.34 K, respectively. The ac magnetic susceptibility of diluted sample 3Dy0.05Y0.95 confirmed the single molecule original relaxation, in which the quantum tunneling of magnetization (QTM) was suppressed efficiently and a butterfly-shaped hysteresis loop at 1.8 K was observed.

Amplified and suppressed regional imprints of global warming events on the southeastern Tibetan Plateau during MIS 3–2

Large amplitude, rapid climate oscillations, the so-called Dansgaard-Oeschger (D-O) events, are characteristic of the last glacial period. However, lithological evidence of D-O warming events is rare, mainly due to their brevity. Although the Tibetan Plateau (TP) is regarded as especially sensitive to climate change owing to its fragile cryosphere and ecological systems, little is known about the variability of the Indian summer monsoon (ISM) over the TP on millennial to centennial timescales. Here, we use a well-dated loess-paleosol sequence (LPS) in the Niyang River valley on the southeastern TP (SE TP), China, to determine the patterns and timing of millennial-to centennial-scale variations in paleomonsoon strength and to identify their causes. This stratigraphic sequence developed between 39.2 and 21.8 cal kyr BP, covering the late marine isotope stage (MIS) 3/2 transition. Ten paleosol units were identified within the sequence, based on field observations, high-resolution measurements of color, grain size and magnetic properties, as well as mineralogical and geochemical evidence. These paleosol units provide unambiguous evidence of D-O-like abrupt warming events and repeated climatic instability, associated with large-amplitude, abrupt changes of the ISM system over the SE TP. The amplitudes, duration, and frequency of these abrupt ISM strengthening events over the SE TP present unique features, including irregular spacing and varying amplitudes. In general, the amplitude of ISM oscillations was larger during MIS 2 than in the late MIS 3 period. Four well-developed paleosol units suggest that ISM intensity at ∼38.7, 28.3, 25.9 and 23.5 cal kyr BP was notably higher compared to the climate of the Holocene, including the present-day. However, two substantial abrupt warming events of global scale are not recorded within the LZ2 LPS. We suggest that this was because of the amplification and suppression of global warming events over the SE TP, caused by the interplay of global and regional climatic dynamics. Warming amplification occurred during intervals with less snow and glacier ice cover, whereas warming suppression was the result of unusually large snow and glacier ice cover on the TP. We suggest that anomalous fluctuations of the India-Burma Trough of the westerlies to the south of the TP during winter may have played a crucial role in determining the snowfall, snow cover, glacier accumulation, and the transition from warming amplification to warming suppression. Therefore, the anomalous ISM oscillations in the SE TP were the result of the coupling of global and local processes.

The effect of thickness of niobium isolation layer on properties of copper-based Nb3Sn films

Copper-based Nb3Sn film is a promising material for applications in the field of superconducting radio frequency (SRF). However, the interdiffusion of copper (Cu) from the substrates into the Nb3Sn films affects the superconductivity of the samples, and the preparation of Nb3 Sn–Nb–Cu composite films is a good solution. In this paper, the effects of the niobium (Nb) layer thickness on Cu interdiffusion and the critical temperature of Nb3Sn film were investigated. Nb3 Sn–Nb films were deposited on Cu substrates by magnetron sputtering. The obtained samples have been characterized via focused ion beam (FIB), time of flight secondary ion mass spectrometry (TOF-SIMS), and magnetic property measurement system (MPMS). It was found that the thicker the Nb isolation layer, the stronger the hindrance effect on the Cu interdiffusion and the higher the critical temperature. A suitable Nb isolation layer thickness was 2.6μm, which effectively hindered the Cu interdiffusion, corresponding to a critical temperature of 16.6 K for the samples.

Localized magnetic properties measurement of interlocking core laminations

PurposeIn rotational alternating current machines, interlocking is a commonly used manufacturing method to fix laminated silicon steel cores. The purpose of this study is to measure the localized magnetic properties more comprehensively and to analyze the deteriorated magnetic properties caused by interlocking more accurately.Design/methodology/approachA movable B–H sensor is designed in this paper. The localized magnetic properties measurement was performed to investigate the magnetic properties around the interlocks with various sizes, various orientations and various numbers of laminations. Then, the damaged area caused by the interlocking was quantified, and the magnetic degradation of different degrees is layered.FindingsThe measurement results have shown that the interlocks with larger sizes, along the transverse direction and on 10-layer laminate, will lead to more serious magnetic degradation, and the maximum loss increment can reach up to 70%.Originality/valueThis work is an improvement and optimization based on the previous overall magnetic measurement of the interlock. The quantitative results of the localized magnetic measurement will have a certain significance for the accurate modeling and simulation of the electrical machines and provide valuable guidance for the optimization of the actual production process of the motor.

Macrospin model of an assembly of magnetically coupled core-shell nanoparticles

Highly sophisticated synthesis methods and experimental techniques allow for precise measurements of magnetic properties of nanoparticles that can be reliably reproduced using theoretical models. Here, we investigate the magnetic properties of ferrite nanoparticles by using theoretical techniques based on Monte Carlo methods. We introduce three stages of sophistication in the macromagnetic model. First, by using tailor-made hamiltonians we study single nanoparticles. In a second stage, the internal structure of the nanoparticle is taken into consideration by defining an internal (core) and external (shell) region, respectively. In the last stage, an assembly of core/shell NPs are considered. All internal magnetic couplings such as inter and intra-atomic exchange interactions or magnetocrystalline anisotropies have been estimated. Moreover, the hysteresis loops of the aforementioned three cases have been calculated and compared with recent experimental measurements. In the case of the assembly of nanoparticles, the hysteresis loops together with the zero-field cooling and field cooling curves are shown to be in a very good agreement with the experimental data. The current model provides an important tool to understand the internal structure of the nanoparticles together with the complex internal spin interactions of the core-shell ferrite nanoparticles.

Investigation of Structural and Electronic Changes Induced by Postsynthesis Thermal Treatment of LiNiO2

Postsynthesis thermal treatments at various temperatures in air have been applied to LiNiO2, and the induced structural and electronic changes have been uncovered. Except for the familiar decomposition process at higher temperatures, a series of transformations also take place under mild conditions. To identify such subtle changes, ex situ and in situ synchrotron radiation diffraction, ex situ 7Li nuclear magnetic resonance spectroscopy, and ex situ measurements of magnetic properties have been performed. We show that the reaction between LiNiO2 and CO2 starts already at a temperature of 200 °C, forming Li1–zNi1+zO2 layers. If the thickness of this layer is well adjusted, the electrochemical performance of LiNO2 can be improved. A cation off-stoichiometry of [Li0.90Ni0.10]NiO2 is identified at 600 °C even before the decomposition occurs. We also investigate the interplay of the reaction between LiNiO2 and CO2 with the decomposition at 700 °C. The changes in the Ni oxidation state and local Li environments are also monitored during the whole process.