165 research outputs found
Anomalous Thermal Transport of SrTiO Driven by Anharmonic Phonon Renormalization
SrTiO has been extensively investigated owing to its abundant degrees of
freedom for modulation. However, the microscopic mechanism of thermal transport
especially the relationship between phonon scattering and lattice distortion
during the phase transition are missing and unclear. Based on deep-potential
molecular dynamics and self-consistent \textit{ab initio} lattice dynamics, we
explore the lattice anharmonicity-induced tetragonal-to-cubic phase transition
and explain this anomalous behavior during the phase transition. Our results
indicate the significant role of the renormalization of third-order interatomic
force constants to second-order terms. Our work provides a robust framework for
evaluating the thermal transport properties during structural transformation,
benefitting the future design of promising thermal and phononic materials and
devices
Universality of the surface magnetoelectric effect in half-metals
An electric field applied to a ferromagnetic metal produces a surface magnetoelectric effect originating from the spin-dependent screening of the electric field which results in a change in the surface magnetization of the ferromagnet
Size dependent electric voltage-controlled magnetic anisotropy in multiferroic heterostructures: Interface-charge and strain co-mediated magnetoelectric coupling
We present a phenomenological scheme to study the size-dependent electric
voltage-controlled magnetic anisotropy in ferromagnetic (FM)/ferroelectric (FE)
heterostructures. The FM layers are either metallic Fe(001), Ni(001), Co(0001),
or half-metallic (La, Sr)MnO3 films. Two magnetoelectric mechanisms, i.e.,
interface-charge and strain-mediated couplings, are considered. We show that
the interface-charge mediated coupling is the main mechanism for the
magnetoelectic coupling when the FM film thickness is below a certain
transition thickness dtr while the strain-mediated coupling dominates above
dtr.Comment: 10 pages, 4 figure
Nanoscale Bandgap Tuning across an Inhomogeneous Ferroelectric Interface
We report nanoscale bandgap engineering via a local strain across the
inhomogeneous ferroelectric interface, which is controlled by the
visible-light-excited probe voltage. Switchable photovolatic effects and the
spectral response of the photocurrent were explore to illustrate the reversible
bandgap variation (~0.3eV). This local-strain-engineered bandgap has been
further revealed by in situ probe-voltage-assisted valence electron energy-loss
spectroscopy (EELS). Phase-field simulations and first-principle calculations
were also employed for illustration of the large local strain and the bandgap
variation in ferroelectric perovskite oxides. This reversible bandgap tuning in
complex oxides demonstrates a framework for the understanding of the
opticallyrelated behaviors (photovoltaic, photoemission, and photocatalyst
effects) affected by order parameters such as charge, orbital, and lattice
parameters
High‐Entropy Lithium Argyrodite Solid Electrolytes Enabling Stable All‐Solid‐State Batteries
Superionic solid electrolytes (SEs) are essential for bulk-type solid-state battery (SSB) applications. Multicomponent SEs are recently attracting attention for their favorable charge-transport properties, however a thorough understanding of how configurational entropy (ΔSconf) affects ionic conductivity is lacking. Here, we successfully synthesized a series of halogen-rich lithium argyrodites with the general formula Li5.5PS4.5ClxBr1.5-x (0≤x≤1.5). Using neutron powder diffraction and 31P magic-angle spinning nuclear magnetic resonance spectroscopy, the S2−/Cl−/Br− occupancy on the anion sublattice was quantitatively analyzed. We show that disorder positively affects Li-ion dynamics, leading to a room-temperature ionic conductivity of 22.7 mS cm−1 (9.6 mS cm−1 in cold-pressed state) for Li5.5PS4.5Cl0.8Br0.7 (ΔSconf=1.98R). To the best of our knowledge, this is the first experimental evidence that configurational entropy of the anion sublattice correlates with ion mobility. Our results indicate the possibility of improving ionic conductivity in ceramic ion conductors by tailoring the degree of compositional complexity. Moreover, the Li5.5PS4.5Cl0.8Br0.7 SE allowed for stable cycling of single-crystal LiNi0.9Co0.06Mn0.04O2 (s-NCM90) composite cathodes in SSB cells, emphasizing that dual-substituted lithium argyrodites hold great promise in enabling high-performance electrochemical energy storage
Magnetic-dielectric properties of NiFe2O4/PZT particulate composites
Particulate composites of lead–zirconate–titanate (PZT) and NiFe2O4 were prepared using conventional ceramic processing. The measured magnetoelectric (ME) response demonstrated strong dependence on the volume fraction of NiFe2O4 , the magnetic field, and the angle between the magnetic field and polarization in the ceramics. A large ME voltage coefficient of about 80 m V cm −1 Oe−1 was observed for 0.32NiFe2O4/0.68PZT composite ceramic. In particular, at low magnetic fields, the ceramics were found to have a large ME response, linearly varying with both dc and ac magnetic fields
Photocatalytic and Magnetic Behaviors Observed in BiFeO 3
Perovskite-type BiFeO3 nanofibers with wave nodes-like morphology were prepared by electrospinning. The nanofibers show a highly enhanced visible-light-active photocatalytic property. The results also showed that the diameter could affect the band gap and photocatalytic performances of nanofibers. Additionally, weak ferromagnetic behaviors can be observed at room temperature, which should be correlated to the size-confinement effect on the magnetic ordering of BiFeO3 structure
Single-atom-layer traps in a solid electrolyte for lithium batteries
In order to fully understand the lithium-ion transport mechanism in solid electrolytes for batteries, not only the periodic lattice but also the non-periodic features that disrupt the ideal periodicity must be comprehensively studied. At present only a limited number of non-periodic features such as point defects and grain boundaries are considered in mechanistic studies. Here, we discover an additional type of non-periodic feature that significantly influences ionic transport; this feature is termed a “single-atom-layer trap” (SALT). In a prototype solid electrolyte Li0.33La0.56TiO3, the single-atom-layer defects that form closed loops, i.e., SALTs, are found ubiquitous by atomic-resolution electron microscopy. According to ab initio calculations, these defect loops prevent large volumes of materials from participating in ionic transport, and thus severely degrade the total conductivity. This discovery points out the urgency of thoroughly investigating different types of non-periodic features, and motivates similar studies for other solid electrolytes
Atomically Intimate Contact between Solid Electrolytes and Electrodes for Li Batteries
Solid electrolytes, as a promising replacement for the flammable liquid electrolyte in conventional Li-ion batteries, may greatly alleviate the safety issues and improve the energy density. However, mainstream electrodes are also solid. If solid electrolytes were employed, creating intimate electrode-electrolyte contact similar to that between solid and liquid would be quite difficult. Here we discovered that, by forming epitaxial interfaces, such a seamless solid-solid contact can happen between two widely studied systems: the Li-rich layered electrode and perovskite solid electrolyte. Atomic-resolution electron microscopy unambiguously demonstrated that the former can be epitaxially embedded into the latter. The solid-solid composite electrode formed this way exhibited a rate capability no lower than the one based on solid-liquid contact. With the periodic misfit dislocations reconciling structural differences, such epitaxy can tolerate large lattice mismatch, and thus may occur between many layered electrodes and perovskite solid electrolytes
Improved electrochemical performance of 5 V spinel LiNi0.5Mn1.5O4 microspheres by F-doping and Li4SiO4 coating
AbstractPorous spinel LiNi0.5Mn1.5O4 microspheres were synthesized by a co-precipitation method. F-doping and Li4SiO4-coating were used as two effective ways to enhance the electrochemical performance of LiNi0.5Mn1.5O4 at both room temperature and elevated temperature. All the samples were characterized by thermogravimetric analysis/differential scanning calorimetry (TG/DSC), X-ray diffraction (XRD), inductive coupled plasma-atomic emission spectroscopy (ICP-AES), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical tests, respectively. According to the SEM images, the LiNi0.5Mn1.5O4 microspheres are hollow with porous shell, and each microsphere is made up of nano-sized spinel grains. This hollow and porous structure favors the sufficient contact between electrolyte and the cathode material. It is indicated that 2 wt.% Li4SiO4-coated LiNi0.5Mn1.5O3.98F0.02 exhibits more superior performance than the pristine one. The doped fluorine ions that enhance the bonding can stabilize the structure of cathode material. The Li4SiO4 coating can suppress side reactions between electrolyte and cathode material as a protective material, and it is a superionic conductor with a three-dimensional lithium ion transfer network to decrease the charge-transfer resistance. The discharge capacity retention of 2 wt.% Li4SiO4-coated LiNi0.5Mn1.5O3.98F0.02 is 97.8% at 25 °C and 94.2% at 55 °C after 150 cycles, respectively
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