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Avdeev, Maxim

Publications and source records attributed to Avdeev, Maxim.

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Structural and Electrochemical Impacts of Mg/Mn Dual Dopants on the LiNiO 2 Cathode in Li-Metal Batteries

Doping chemistry has been regarded as an efficient strategy to overcome some fundamental challenges facing the “no-cobalt” LiNiO 2 cathode materials. By utilizing the doping chemistry, we evaluate the battery performance and structural/chemical reversibility of a new no-cobalt cathode material (Mg/Mn-LiNiO 2 ). The unique dual dopants drive Mg and Mn to occupy the Li site and Ni site, respectively. We report the Mg/Mn-LiNiO 2 cathode delivers smooth voltage profiles, enhanced structural stability, elevated self-discharge resistance, and inhibited nickel dissolution. As a result, the Mg/Mn-LiNiO 2 cathode enables improved cycling stability in lithium metal batteries with the conventional carbonate electrolyte: 80% capacity retention after 350 cycles at C /3, and 67% capacity retention after 500 cycles at 2 C (22 °C). We then take the Mg/Mn-LiNiO 2 as the platform to investigate the local structural and chemical reversibility, where we identify that the irreversibility takes place starting from the very first cycle. The highly reactive surface induces the surface oxygen loss, metal reduction reaching the subsurface, and metal dissolution. Our data demonstrate that the dual dopants can, to some degree, mitigate the irreversibility and improve the cycling stability of LiNiO 2 , but more efforts are needed to eliminate the key challenges of these materials for battery operation in the conventional carbonate electrolyte.

25 ENERGY STORAGE↗
DOE OSTI2020

Ultralow thermal conductivity from transverse acoustic phonon suppression in distorted crystalline α-MgAgSb

Low thermal conductivity is favorable for preserving the temperature gradient between the two ends of a thermoelectric material, in order to ensure continuous electron current generation. In high-performance thermoelectric materials, there are two main low thermal conductivity mechanisms: the phonon anharmonic in PbTe and SnSe, and phonon scattering resulting from the dynamic disorder in AgCrSe2 and CuCrSe2, which have been successfully revealed by inelastic neutron scattering. Using neutron scattering and ab initio calculations, we report here a mechanism of static local structure distortion combined with phononanharmonic-induced ultralow lattice thermal conductivity in α-MgAgSb. Since the transverse acoustic phonons are almost fully scattered by the compound’s intrinsic distorted rocksalt sublattice, the heat is mainly transported by the longitudinal acoustic phonons. The ultralow thermal conductivity in α-MgAgSb is attributed to its atomic dynamics being altered by the structure distortion, which presents a possible microscopic route to enhance the performance of similar thermoelectric materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Dopant Distribution in Co-Free High-Energy Layered Cathode Materials

The practical implementation of Co-free, LiNiO 2 -derived cathodes has been prohibited by their poor cycle life and thermal stability, concluded from the structural instability, phase transformations, reactive surfaces, and chemomechanical breakdown. With the hierarchical distribution of Mg/Ti dual dopants in LiNiO 2 , we report a Co-free layered oxide that exhibits enhanced bulk and surface stability. Ti shows a gradient distribution and is enriched at the surface, whereas Mg distributes homogeneously throughout the primary particles. The resulting Mg/Ti codoped LiNiO 2 delivers a material-level specific energy of ~780 W h/kg at C/10 with 96% retention after 50 cycles. The specific energy reaches ~680 W h/kg at 1C with 77% retention after 300 cycles. Furthermore, the Mg/Ti dual dopants improve the rate capability, thermal stability, and self-discharge resistance of LiNiO 2 . Our synchrotron X-ray, electron, and electrochemical diagnostics reveal that the Mg/Ti dual dopants mitigate phase transformations, reduce nickel dissolution, and stabilize the cathode–electrolyte interface, thus leading to the favorable battery performance in lithium metal and graphite cells. The current study suggests that engineering the dopant distribution in cathodes may provide an effective path toward lower cost, safer, and higher energy density Co-free lithium batteries.

25 ENERGY STORAGE↗
DOE OSTI2019

An Ordered P2/P3 Composite Layered Oxide Cathode with Long Cycle Life in Sodium-Ion Batteries

Developing stable cathode materials represents a crucial step toward long-life sodium-ion batteries. P2-type layered oxides are important as cathodes for their reversibility, but their long-term performance in full cells remains a key challenge. Herein, we report Na 0.75 Co 0.125 Cu 0.125 Fe 0.125 Ni 0.125 Mn 0.5 O 2 with an intergrowth of ordered P2 and P3 phases, studied by neutron diffraction and Rietveld refinement. A stable electrochemical performance is achieved in Na half cells with 100% capacity retention at a rate of C/10 after 100 cycles (initial capacity of 90 mAh/g), 96% capacity retention at a rate of 1 C after 500 cycles (initial capacity of 70 mAh/g), and 85% capacity retention at a rate of 5 C after 1000 cycles (initial capacity of 55 mAh/g). Stable full cell performance is achieved with 84.2% capacity retention after 1000 cycles at a rate of 1 C. Synchrotron X-ray diffraction, spectroscopy, and imaging are applied to elucidate the relationship between chemical/structural evolution and battery performance. A reversible local and global structural evolution is observed during initial cycles. Meanwhile, the challenges with enabling prolonged cycling (beyond 1000 cycles) may be associated with Fe dissolution and formation of a copper oxide phase. This study implies that cathodes with complex chemical and structural formations may stabilize electrochemical performance and highlights the importance of decoupling the contribution of each transition metal to performance degradation.

25 ENERGY STORAGE↗
DOE OSTI2019

Neutron scattering study of the quasi-one-dimensional antiferromagnet Ba 2 CoSi 2 O 7

Magnetization and neutron scattering measurements have been carried out on an antiferromagnet Ba 2 CoSi 2 O 7 . The observed magnetic excitation is almost dispersionless, and the neutron intensity is only modulated along the [101] direction. The dispersionless magnetic excitation suggest that the Ba 2 CoSi 2 O 7 system is a quasi-one-dimensional antiferromagnet. Classical spin-wave theory for a one-dimensional antiferromagnet can explain the dispersionless spin excitation. Additionally, the magnetic structure determined by the measurement of the neutron powder diffraction is consistent with no observation of the multiferroic property in this system.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Correlated Migration Invokes Higher Na + ‐Ion Conductivity in NaSICON‐Type Solid Electrolytes

Abstract Na super ion conductor (NaSICON), Na 1+ n Zr 2 Si n P 3– n O 12 is considered one of the most promising solid electrolytes; however, the underlying mechanism governing ion transport is still not fully understood. Here, the existence of a previously unreported Na5 site in monoclinic Na 3 Zr 2 Si 2 PO 12 is unveiled. It is revealed that Na + ‐ions tend to migrate in a correlated mechanism, as suggested by a much lower energy barrier compared to the single‐ion migration barrier. Furthermore, computational work uncovers the origin of the improved conductivity in the NaSICON structure, that is, the enhanced correlated migration induced by increasing the Na + ‐ion concentration. Systematic impedance studies on doped NaSICON materials bolster this finding. Significant improvements in both the bulk and total ion conductivity (e.g., σ bulk = 4.0 mS cm −1 , σ total = 2.4 mS cm −1 at 25 °C) are achieved by increasing the Na content from 3.0 to 3.30–3.55 mol formula unit −1 . These improvements stem from the enhanced correlated migration invoked by the increased Coulombic repulsions when more Na + ‐ions populate the structure rather than solely from the increased mobile ion carrier concentration. The studies also verify a strategy to enhance ion conductivity, namely, pushing the cations into high energy sites to therefore lower the energy barrier for cation migration.

Zhang, Zhizhen↗
DOE OSTI2019

Surface Characterization of Li-Substituted Compositionally Heterogeneous NaLi 0.045 Cu 0.185 Fe 0.265 Mn 0.505 O 2 Sodium-Ion Cathode Material

The understanding of surface chemical and structural processes can provide some insights into designing stable sodium cathode materials. Herein, Li-substituted and compositionally heterogeneous NaLi 0.045 Cu 0.185 Fe 0.265 Mn 0.505 O 2 is used as a platform to investigate the interplay between Li substitution, surface chemistry, and battery performance. Li substitution improves the initial discharge capacity and energy density. Yet, there is no noticeable benefit in the long-term cycling stability of this material. The Li substitution in the transition-metal (TM) layer also seems to influence the transition-metal (TM) 3d–oxygen (O) 2p hybridization. Upon desodiation, the surface of active particles undergoes significant transition-metal reduction, especially Mn. Furthermore, the presence of electrolyte drastically accelerates such surface degradation. In general, the Li-substituted material experiences severe surface degradation, which is partially responsible for the performance degradation upon long-term cycling. While some studies have introduced the benefits of Li substitution, the present study suggests that the effectiveness of the Li substitution strategy depends on the TM compositional distribution. More efforts are needed to improve the surface chemistry of Li-substituted sodium cathode materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Spatially limited antiferromagnetic order in a cluster glass compound Tb2Ni0.90Si2.94

In the present study, the synthesis of a new ternary intermetallic compound Tb2Ni0:90Si2:94 has been reported. The detailed studies on structure, static and dynamical magnetic properties of the compound have been investigated by means of powder x-ray diffraction, compositional analysis, dc & ac magnetization, non-equilibrium dynamics, heat capacity and neutron diffraction measurements. The dc & ac magnetic susceptibility reveal that the compound undergoes spin cluster-glass behaviour below 9.9 K. The frequency dependence of the freezing temperature have been analyzed on the basis of dynamic scaling laws such as power-law divergence and Vogel-Fulcher law, which further con rm the cluster-glass state formation for the compound. A detailed study on non-equilibrium dynamical behaviour associated with cluster-glass state has been carried out through magnetic relaxation behaviour along with magnetic memory effect in zero-field-cooled (ZFC) as well as field-cooled (FC) conditions and associated aging effect. The zero-field neutron diffraction study reveals the presence of a spatially limited antiferromagnetic phase in addition to the magnetically frustrated cluster-glass state. This result has also been supported through zero-field heat capacity studies. The variation in local electronic environment among the magnetic rare- earth ions caused by the structural disorder associated with Ni/Si ions have been argued to be responsible for the coexistence of different magnetic phases.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Crystal structure and monoclinic distortion of glaserite-type Ba{sub 3}MnSi{sub 2}O{sub 8}

Highlights: • Glaserite-type Ba{sub 3}MnSi{sub 2}O{sub 8} is hexagonal P-3m1 at room temperature. • Below ~ 250 K the structure undergoes transition to monoclinic C2/c. • The transition is driven by in-plane displacement of the apical oxygen atoms. • No magnetic transition was observed down to 1.6 K but expected at lower temperature. - Abstract: Crystal structure and magnetic properties of glaserite-type Ba{sub 3}MnSi{sub 2}O{sub 8} were investigated using variable temperature neutron powder diffraction and magnetometry. At room temperature the composition is hexagonal and the crystal structure is best described by the P-3m1 space group (a~ 5.7 Å, c~ 7.3 Å) with the apical oxygen atom modelled on a split site. On cooling below ~ 250 K the structure undergoes a phase transition into a monoclinic C2/c form (√3a{sub hex}, a{sub hex}, 2c{sub hex}, β~ 90°). Analysing diffraction data in terms of symmetry-adapted distortion modes suggests that the transition is primarily driven by increasing in-plane displacements of O1, which in turn results in the coupled tilting of [SiO{sub 4}] and [MnO{sub 6}] octahedra and in-plane displacements of Ba1 atoms. Magnetic susceptibility measurements and neutron powder diffraction data show no evidence for long-range magnetic ordering down to 1.6 K, although the development of magnetic diffuse scattering suggests that a magnetic transition may take place at lower temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Magnetic properties of CeM{sub 1.5}M’{sub 0.5}Ge{sub 4}O{sub 12} (M = Mn, Co; M’ = Ni, Cu)

Highlights: • marked composition dependence of magnetic structure. • metamagnetic transition in CeCo{sub 1.5}Cu{sub 0.5}Ge{sub 4}O{sub 12}. • neutron diffraction in an applied field. - Abstract: A study of the solid solutions CeM{sub 2-x}M’{sub x}Ge{sub 4}O{sub 12} (M = Mn, Co; M’ = Ni, Cu) by X-ray diffraction and magnetometry is described. For M = Co the introduction of Ni and Cu was possible for x ≤ 0.5; for M = Mn attempts to introduce Cu were unsuccessful but CeMn{sub 1.5}Ni{sub 0.5}GeO{sub 4} was obtained as a single phase. These compositions crystallise in the space group P4/nbm with a ~9.76, c ~4.85 Å. They all order antiferromagnetically with T{sub N}1.5 Ni{sub 1.5}Ge{sub 4}O{sub 12} and CeCo{sub 1.5}Cu{sub 0.5}Ge{sub 4}O{sub 12} were shown by neutron diffraction to be the same as those adopted by CeMn{sub 2}Ge{sub 4}O{sub 12} and CeCo{sub 2}Ge{sub 4}O{sub 12}, respectively. The in-field metamagnetic transition of the latter to a weakly ferromagnetic phase was shown to persist in the Cu-doped composition. The available data suggest that the anisotropy associated with the Co{sup 2+} cation plays a dominant role in determining the magnetic behaviour of these compounds.

36 MATERIALS SCIENCE↗
DOE OSTI2018

On Disrupting the Na + -Ion/Vacancy Ordering in P2-Type Sodium–Manganese–Nickel Oxide Cathodes for Na + -Ion Batteries

An investigation of the electrochemical and structural properties of layered P2-Na 0.62 Mn 0.75 Ni 0.25 O 2 is presented. The effect of changing the Mn:Ni ratio (3:1) from what is found in Na 0.67 Mn 0.67 Ni 0.33 O 2 (2:1) and consequently the introduction of a third metal center (Mn 3+ ) was investigated. X-ray diffraction ( in-situ and powder) revealed the lack of Na+-ion/vacancy ordering at the relevant sodium contents (x = 0.33, 0.5 and 0.67). The Mn 3+ in Na 0.62 Mn 0.75 Ni 0.25 O 2 introduces defects into the Ni-Mn inter-plane charge order that in turn disrupts the ordering within the Na-plane. The material underwent a P2-O2 and P2-P2’ phase transition at high (4.2 V) and low (~ 1.85 V) voltages, respectively. The material was tested at several different voltage ranges in order to understand the effect of the phase transitions on the capacity retention. Interestingly, the inclusion of both phase transitions demonstrated comparable cycling performance to when both phase transitions were excluded. As a result, excellent rate performance was demonstrated between 4.3 – 1.5 V with a specific capacity of 120 mAh/g delivered at 500 mA/g current density.

25 ENERGY STORAGE↗
DOE OSTI2018

Synthesis and structural characterization of the vividly colored first row transition metal-containing oxyfluoride antiperovskites Sr3-xMnxMO4F and Sr3-xMnxMO4-αF1-δ (M = Al, Ga)

Highlights: • Substitution of Mn{sup 2+} demonstrates Sr{sub 3-x}A{sub x}MO{sub 4}F can tolerate divalent first row transition metals. • The colors of these materials vary from green to purple depending on anion stoichiometry. • Intense colors are likely due to small amounts of Mn{sup 3+} on the tetrahedral Al site. • Structural data is consistent with preferential occupation of eight-coordinate Sr(2) site by Mn{sup 2+}. • Large off-center displacements are observed on the underbonded ten-coordinate Sr(1) site. - Abstract: Incorporation of dopant amounts of the divalent transition metal cation Mn{sup 2+} into the oxyfluoride material Sr{sub 3-x}Mn{sub x}MO{sub 4}F (M = Al, Ga; 0 ≤ x ≤ 0.1) yields green powders which vary in hue depending on the identity of M. Treatment of these phases with post-synthesis annealing under reducing conditions produces anion deficient phases according to Sr{sub 3-x}Mn{sub x}MO{sub 4-α}F{sub 1-δ} displaying vivid purple coloration. Intense colors are likely due to small amounts of Mn{sup 3+} on the tetrahedral M site. Full structural characterization based upon powder X-ray diffraction (PXRD), neutron powder diffraction (NPD), and thermogravimetric analysis (TGA) data are presented herein, demonstrating that the Sr{sub 3-x}A{sub x}MO{sub 4}F (A = Ca, Sr, Ba; M = Al, Ga) anti-perovskite structure can readily accommodate first row transition metals.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Magnetic properties of the 6H perovskite Ba{sub 3}Fe{sub 2}TeO{sub 9}

A polycrystalline sample of Ba{sub 3}Fe{sub 2}TeO{sub 9} having the 6H perovskite structure has been prepared in a solid-state reaction and studied by a combination of electron microscopy, Mössbauer spectroscopy, magnetometry, X-ray diffraction and neutron diffraction. Partial ordering of Fe{sup 3+} and Te{sup 6+} cations occurs over the six-coordinate sites; the corner-sharing octahedra are predominantly occupied by the former and the face-sharing octahedra by a 1:1 mixture of the two. On cooling through the temperature range 18 < T/K < 295 an increasing number of spins join an antiferromagnetic backbone running through the structure while the remainder show complex relaxation effects. At 3 K an antiferromagnetic phase and a spin glass coexist. - Graphical abstract: On cooling an increasing number of spins join an antiferromagnetic backbone running through the structure while the remainder show complex relaxation effects. Display Omitted - Highlights: • Rapid spin relaxation occurs over a wide temperature range below the Néel temperature. • Magnetic moments on two cation sublattices develop at significantly different rates. • Centrosymmetric structure is confirmed by electron microscopy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Synthesis and structural characterization of the hexagonal anti-perovskite Na{sub 2}CaVO{sub 4}F

The structural details of the ordered hexagonal oxyfluoride Na{sub 2}CaVO{sub 4}F prepared by solid-state synthesis using stoichiometric amounts of V{sub 2}O{sub 5}, CaCO{sub 3}, Na{sub 2}CO{sub 3} and NaF were characterized using high-resolution neutron powder diffraction. The structural changes between 25 °C and 750 °C revealed that the two structural subunits in this material behave different when heated: there is an expansion of the face-shared FNa{sub 4}Ca{sub 2} octahedra while the VO{sub 4} tetrahedra due to increased thermal disorder reveal marginal bond contractions. Bond valences and the global instability index point to significant structural disorder at 750 °C. - Graphical abstract: The structure of the novel oxyfluoride Na{sub 2}CaVO{sub 4}F is studied at room temperature and high-temperatures. The structure can be viewed as layers of compression and elongation of polyhedral subunits, which change as a function of temperature. - Highlights: • The novel oxyfluoride, Na{sub 2}CaVO{sub 4}F, is synthesized via solid-state method. • High-resolution neutron diffraction data is used to analyze the structure of Na{sub 2}CaVO{sub 4}F. • Structural subunits exhibit expansion and contraction with increasing temperature. • Higher temperatures increase instability within the structure of Na{sub 2}CaVO{sub 4}F.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

The impact of chemical doping on the magnetic state of the Sr{sub 2}YRuO{sub 6} double perovskite

The impact of chemical doping of the type Sr{sub 2−x}A{sub x}YRuO{sub 6} (A=Ca, Ba) on the low temperature magnetic properties of Sr{sub 2}YRuO{sub 6}, probed using variable temperature magnetic susceptibility, neutron diffraction and heat capacity measurements, are described. Specific-heat measurements of un-doped Sr{sub 2}YRuO{sub 6} reveal two features at ∼26 and ∼30 K. Neutron scattering measurements at these temperatures are consistent with a change from a 2D ordered state to the 3D type 1 AFM state. Magnetic and structural studies of a number of doped oxides are described that highlight the unique low temperature behavior of Sr{sub 2}YRuO{sub 6} and demonstrate that doping destabilizes the intermediate 2D ordered state. - Graphical abstract: Neutron diffraction measurements of the ordered double perovskite Sr{sub 2}YRuO{sub 6}reveal a with a change from a 2D ordered state to the 3D type 1 AFM state upon cooling. The impact of chemical doping Sr{sub 2−x}A{sub x}YRuO{sub 6} (A=Ca, Ba) on the low temperature magnetic properties have also been investigated and these highlight the unique low temperature behavior of Sr{sub 2}YRuO{sub 6} with doping destabilizing the intermediate 2D ordered state. - Highlights: • Crystal and Magnetic Structure of Sr{sub 2}YRuO{sub 3} was studied using Neutron Diffraction. • Effect of doping on the magnetic ground state established. • Origin of two low temperature transitions discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Structural and spectroscopic studies of Ba{sub 2}Y{sub 1−δ}UO{sub 6+x}

A combination of S-XRD and NPD demonstrate the structure of Ba{sub 2}Y{sub 0.879}UO{sub 6+x} to be monoclinic in space group I2/m. That the U is hexavalent is evident from the U L{sub 2}-edge XANES measurements. This appears to be a rare example of a double perovskite containing vacancies at the octahedral B-sites and interstitial oxygen defects, which combine to stabilise hexavalent U and appears to be a consequence of the preparation of the sample in air. The Y vacancies, coupled with anion disorder, results in a distortion of the BO{sub 6} octahedra. - Graphical abstract: The structure of Ba{sub 2}Y{sub 0.879}UO{sub 6+x} is shown to be a rare example of a double perovskite containing vacancies at the octahedral B-sites and interstitial oxygen defects. - Highlights: • Structure of Ba{sub 2}Y{sub 0.879}UO{sub 6+x} refined. • U L-edge XANES demonstrates the U is hexavalent. • Rare example of a perovskite containing vacancies at the octahedral B-site. • Y vacancies result in a distortion of the BO{sub 6} octahedra.

36 MATERIALS SCIENCE↗