Anomalous Thermal Transport of SrTiO3_3 Driven by Anharmonic Phonon Renormalization

SrTiO$_3$ 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

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

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

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

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

Screening Spin Lattice Interaction Using Deep Learning Approach

Atomic simulations hold significant value in clarifying crucial matters such as phase transitions and energy transport in materials science. Their success stems from the presence of potential energy functions capable of accurately depicting the relationship between system energy and lattice changes. In magnetic materials, two atomic scale degrees of freedom come into play: the lattice and the magnetic moment. Nonetheless, precisely portraying the interaction energy and its impact on lattice and spin-driving forces, such as atomic force and magnetic torque, remains a formidable task in the computational domain. Consequently, there is no atomic-scale approach capable of elucidating the evolution of lattice and spin at the same time in magnetic materials. Addressing this knowledge deficit, we present DeepSPIN, a versatile approach that generates high-precision predictive models of energy, atomic forces, and magnetic torque in magnetic systems. This is achieved by integrating first-principles calculations of magnetic excited states with advanced deep learning techniques via active learning. We thoroughly explore the methodology, accuracy, and scalability of our proposed model in this paper. Our technique adeptly connects first-principles computations and atomic-scale simulations of magnetic materials. This synergy presents opportunities to utilize these calculations in devising and tackling theoretical and practical obstacles concerning magnetic materials.Comment: 8 pages, 4 figure