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The anionic (oxygen) redox is known responsible for the high specific capacity and the transition metal (TM) migration of the Li- and Mn-rich (LMR) layer-structured oxide cathode materials. The reversibility of the TM redox was taken for granted; less attention has been paid to the relationship between structural degradation (TM migration and oxygen loss) and the redox behavior of the TM ions at low potentials. In combination of the crystalline and electronic structural characterizations and the electrochemical evaluation, we revealed in this article that the TM migration (Li-TM mixing) and the intensive anionic oxidation at high potentials suppress the Co2+/3+ redox and trigger the Mn3+/4+ redox at low potentials. The Mn3+/4+ redox accelerates the structural distortion and reduces the average discharge potential though both the Co2+/3+ and Mn3+/4+ redox contribute to charge compensation and the total capacity. Slightly decreasing the initial delithiation (charge cut-off potential decreases to 4.6 V vs. Li+/Li) mitigates the TM migration in Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 and significantly improves its structural stability and cycling performance after the charge cut-off potential recovers to the "normal" value (4.8 V) in the subsequent cycling. The dependence of the electronic structure of the Co 3d and Mn 3d orbitals on structural degradation is clarified with the density functional theory (DFT) calculations. It was shown that the TM migration in LMR results in the decrease of the unoccupied states of the Co 3d orbitals and the shifting of the unoccupied states of the Mn 3d orbital towards the Fermi energy level. These findings reveal the correlation between the structural degradation and the behavior of the low-potential TM redox, and will inspire ways to excavate a higher capacity in LMRs by activating more TM redox couples. [Display omitted] • The behavior of the Mn3+/4+ and Co2+/3+ redox is correlated with the structural degradation of Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2. • The TM migration (Li-TM mixing) and the intensive anionic oxidation at high potentials suppress the Co2+/3+ redox and trigger the Mn3+/4+ redox at low potentials. • The activation of Co2+/3+ redox by mitigating the structural degradation further improves the capacity of Li-rich cathodes (314 mAh g-1 at 0.1 C). [ABSTRACT FROM AUTHOR]

The Ni-rich layer-structured oxide is one of the most promising candidate cathode materials for the high energy-density Li-ion batteries. However, the commercial applications of these materials are hindered with drawbacks such as structural instability and poor cycling performance at high potentials. Herein, we comprehensively studied the oxygen redox reaction and the structural reversibility of LiNi 0.83 Co 0.12 Mn 0.05 O 2 at deep delithiation using the synchrotron X-ray absorption spectroscopy, scanning transmission electron microscopy and density functional theory calculations. The oxygen redox occurs due to the cation mixing upon delithiation in this material though there are no Li-O-Li configurations in its pristine form. The formation of the I 4 1 structure was attributed to the migration of the transition metals in the deeply delithiated material, extending the route of the phase transformation from the layered to the rock-salt structure. These findings are helpful to enrich the understanding of the origin of the oxygen redox and reveal its impact on the structural transformations in the Ni-rich layered oxides. These will spur new strategies to enhance the performance of the cathode materials for the next-generation Li-ion batteries. [Display omitted] • Oxygen redox can occur in the LiNi 0.83 Co 0.12 Mn 0.05 O 2 without Li-O-Li configurations at deep delithiation. • The partially reversible I 4 1 structure are formed near the surface in the deeply delithiated material. • Oxygen redox is coupled with the cation mixing. [ABSTRACT FROM AUTHOR]

Anionic redox is another way of charge compensation to boost the energy density of the cathode materials. In addition to the conventional Li–O–Li configurations in the well-known layered Li-rich transition metal oxides, both the Na–O–Mg and Na–O-vacancy configurations have been found effective in triggering the oxygen redox for charge compensation. Therefore, it will be interesting to compare their superiority in activating the anionic redox reaction. Herein, P2-type Na 2/3 [Mn 7/9 Mg 1/9 □ 1/9 O 2 (□ for vacancy) is designed that contains both vacancies and magnesium ions in its transition metal (TM) layer. The co-existence of equal quantity of vacancies and Mg2+ ions makes it possible to compare the superiority of these two configurations. Soft X-ray absorption spectroscopy and density functional theory calculations demonstrate that the vacancies are superior in facilitating the oxygen redox at low voltage. In addition, the asymmetry and flexibility of the vacancy-containing TMO 6 octahedrons ensure the high structural stability of the material. It delivers a reversible capacity of 212 mAh g−1 between 1.5 and 4.5 V and the reversibility of oxygen redox in 50 cycles between 2.1 V and 4.4 V. The capacity retention is good in 50 cycles between 2.1 V and 4.4 V. The strategy of introducing vacancies in the TMO 2 slab to stabilize the structure and to enhance the anionic redox will inspire new ideas in seeking and designing advanced cathode materials with superior performances. The existence of equal quantities of the Mg2+ ions and vacancies in the TM layer of P2-type Na 2/3 [Mn 7/9 Mg 1/9 □ 1/9 O 2 provides an opportunity to compare their superiorities in triggering the oxygen redox and in stabilizing the structure. Our findings will inspire new ideas in designing new cathode materials with high energy densities and performance stability. Image 1 • A P2-type Na 2/3 [Mn 7/9 Mg 1/9 □ 1/9 O 2 was prepared as a cathode material for the Na-ion batteries. • It contains equal quantities of the Mg2+ ions and vacancies in the TM layer. • The vacancies are found superior to the Mg2+ ions in charge compensation. [ABSTRACT FROM AUTHOR]

Recently, a novel rechargeable Al ion battery (AIB) with high performance has been developed. Owing to its low cost, high-rate capability, excellent cyclability, and non-flammability, AIB provides a safe alternative to many commercial batteries used in the energy storage system. To improve its performance, identifying molecular structure and arrangement of chloroaluminate anion (AlCl 4 −) intercalated in the graphite layer remains a great challenge. In this work, operando analysis of X-ray diffraction (XRD) measurement and X-ray absorption (XAS) spectroscopy were performed to investigate the intercalation of AlCl 4 − anion and related molecular arrangement in the graphite layers. The intercalated stage and intercalant gallery height of graphite cathode electrode during AIB battery operation were observed to be stage 3 and 9.22 Å, respectively. Furthermore, the spectral evolution from ex-situ XAS at the Al and Cl K-edge was associated with closely packed intercalation of AlCl 4 − molecules. With density functional theory (DFT) calculation, three simulated models of intercalated AlCl 4 − molecules in the graphite layer were revealed successfully, which explained possible molecular structures at different charging states. This analytical methodology paves the way for better understanding the structural transformation of molecular ions de-/intercalation in graphite layers. The molecular arrangement structure of AlCl 4 − intercalating into graphite layers under different charging and discharging states has been revealed by operando X-ray spectroscopic technique and core level spectra of DFT simulation. These approaches can also be applied to investigate other intercalating molecular structure of anion or cation molecules in graphite layers for developing next-generation batteries. Image 1 [ABSTRACT FROM AUTHOR]

Stoichiometric gallium ferrite (GFO) is a promising single-phase multiferroic material at room temperature. Nevertheless, simultaneous magnetism and ferroelectricity in a single GFO at room temperature has not been demonstrated yet. In this work, single-phase GFO thin films with different amount of excessive Fe have been successfully grown using a dual target pulsed laser deposition (PLD) process, and the magnetic transition temperature is found to be above room temperature with excessive Fe distributed among the available cation sites of GFO unit cell. Ferroelectricity of GFO films have been confirmed by second harmonic generation (SHG), polarization hysteresis, pyroelectric reversal, and piezoresponse force microscopy (PFM), and magnetoelectric (ME) coupling has been demonstrated by increase in piezoresponse induced via external magnetic field applied in-plane, all measured at room temperature. From the data, it is theorized that the magnetic properties of GFO originate from the superexchange interaction mediated via the Fe1-O-Fe2 bond, and an additional Fe1-O-Fe* bond can form from excess Fe atoms. Under a magnetic field applied along c axis, the magnetic moment of Fe2 and Fe* increase while that of Fe1 decreases, and these changes in magnetic moment result in larger distortion of Fe2 and Fe* octahedrons along the b-axis, and thus enhanced polarization and piezoresponse. This series of studies thus confirm single-phase GFO with excessive Fe as a multiferroic material at room temperature with ME coupling, paving way for its potential functional applications in microelectronic and spintronic devices. [ABSTRACT FROM AUTHOR]

The exchange bias (EB) effect, which is the shift of the hysteresis loop of a ferromagnet in direct contact with an antiferromagnet, is highly advantageous for the development of spintronics applications. Carbon (C) has been considered as a potential material in next generation electronics production as well as spintronics devices beyond silicon. Here we show experimental evidence for an EB in C/Co composites. The significant EB needs thermal annealing to occur. X-ray absorption spectra and transmission electron microscopy data of these samples reveal that Co carbides in as grown samples decompose and form graphitic C/Co interfaces after annealing. Using x-ray magnetic circular dichroism we have detected the C spins that are responsible for the EB. These results inspire a theoretical model to investigate the magnetic interactions in graphitic C/Co interfaces and interpret the observed results. [ABSTRACT FROM AUTHOR]

The present study demonstrates the modification of magnetic anisotropy in cobalt ferrite (CoFe 2 O 4 ) thin films induced by swift heavy ion irradiations of 200 MeV Ag-ion beams. The study reveals that both magnetizations and coercive field are sensitive to Ag-ions irradiation and to the fluences. The magnetic anisotropy enhanced at low fluence of Ag-ions due to domain wall pinning at defect sites created by ion bombardment and at high fluence, this magnetic anisotropy ceases and changes to isotropic behavior which is explained based on the significant structural and morphological changes. An X-ray absorption and x-ray magnetic circular dichroism studies confirms the inverse spinel structure of these compounds. [ABSTRACT FROM AUTHOR]

Understanding the interfacial behavior at FM-OSC-FM hybrid structures for both the bottom contact (Alq 3 adsorption on Co, Co/Alq 3 ) and the top contact (Co atop Alq 3 , Alq 3 /Co) is crucial for efficient spin filtering with transport of spin-polarized charge carriers through these interfaces. X-ray photoelectron spectroscopy (XPS) spectra indicate a symmetry of charge transfer from Co to Alq 3 and the corresponding orbital hybridization to a certain extent at both contacts. The alignment of energy levels at both Alq 3 /Co and Co/Alq 3 heterostructures is depicted with ultraviolet photoelectron spectroscopy (UPS). Through magnetic images acquired with a X-ray photoemission electron microscope (XPEEM), the strong hybridization of the top contact presents no micromagnetic domain but still shows magnetic coupling, to some extent, to the bottom contact in the Co–Alq 3 –Co trilayer structure. Measurements of X-ray magnetic circular dichroism (XMCD) demonstrate the induced spin-polarization of non-magnetic Alq 3 at both contacts, proving Alq 3 a unique and promising organic material for spin filtering in OSV. [ABSTRACT FROM AUTHOR]

Abstract: X-ray absorption measurements have been made on CuL3 and OK edges for two transition metal substituted Hg based oxycarbonates Hg0.5Mo0.5Sr4Cu2(CO3)O6+ δ and Hg0.4Cr0.6Sr4Cu2(CO3)O6+ δ . Despite a much lower T c (37K) the Cr sample has a much higher diamagnetic fraction than the Mo sample (T c∼74K). CuL3 and OK edge spectra clearly indicate the presence of substantial number of doping holes in both the samples characteristic of their superconducting properties. But interestingly, the density of holes (DOH) are almost the same for the two samples. If the DOH correlated with the T c solely, one would expect it be nearly double in Mo sample than the Cr one. Thus the present study presents a strong evidence for the dependence of DOH upon diamagnetic fraction over and above its dependence upon their transition temperature in the cuprate perovskites. Also the results of resistivity and susceptibility studies made earlier on these samples have been mentioned briefly. [Copyright &y& Elsevier]