arXiv subjects

Narendirakumar Narayanan

Publications and source records attributed to Narendirakumar Narayanan.

5 recordsLinked to original sources

arXiv2026

$Ab$ $initio$ Study of Substitutional Defects in Li$_{3}$OCl Solid Electrolyte for Li-ion Batteries

Improving ion transport in solid electrolytes and cathode coatings remains a key challenge for all-solid-state Li-ion batteries because their room-temperature ionic conductivity is still substantially lower than that of liquid electrolytes. In our previous combined experimental and theoretical study, we showed that thermal neutron irradiation enables defect engineering in LiBO$_2$ through the transmutation of $^6$Li and $^{10}$B, generating lattice vacancies that enhance ionic conductivity. Here, we examine whether this approach can be extended to Li$_3$OCl, a representative antiperovskite solid electrolyte. Using density functional theory, we investigate substitutional defects at Li sites involving B, He, and H, associated with B doping and the neutron-capture reactions $^{6}\mathrm{Li}+n\rightarrow\,^{3}\mathrm{H}+α$ and $^{10}\mathrm{B}+n\rightarrow\,^{7}\mathrm{Li}+α+γ$. We evaluate defect formation energetics, the resulting structural distortions, and compare these substitutional defects with other mono-, di-, and trication substitutions at Li sites. Our results show that substitutional defects associated with neutron irradiation provide a feasible route to tune the defect chemistry of antiperovskite solid electrolytes and support neutron-driven defect engineering as a strategy for developing advanced materials for high-performance all-solid-state Li-ion batteries.

cond-mat.mtrl-sci↗

arXiv2026

Neutron-Induced Enhancement of Ion Transport Through Lithium-Ion Battery Materials

Polycrystalline solid-state ionic conductors (SSICs) are essential energy materials for all-solid-state Li-ion batteries. To date, achieving a room-temperature ionic conductivity of solid electrolytes comparable to that of their liquid counterparts remains a critical challenge. Here, we experimentally demonstrate that thermal neutron irradiation can offer an innovative strategy in that neutron-induced modification in an SSIC model (LiBO$_{2}$ as an effective cathode coating) can facilitate ion transport through the material, enhancing its ionic conductivity. The central concept is that high-flux ($\sim 10^{9}\text{ neutrons}\cdot \text{cm}^{-2}\cdot \text{s}^{-1}$) thermal neutrons ($\sim \text{25 meV}$) selectively transmute strong neutron absorbers [which are $^{10}$B (3840 barns) and $^{6}$Li (940 barns) isotopes and present in their natural abundances of $\sim 19.9\%$ and $\sim 7.5\%$, respectively, in polycrystalline grains of LiBO$_2$] to generate lattice vacancies without compromising their crystallographic long-range order. In addition, by-product gamma photons emitted from $^{10}$B transmutation free electrons to stop atomic displacement and simultaneously neutralize the space charge built up by positively-charged oxygen vacancies at grain boundaries. As a result, the ionic conductivity is increased by nearly 20\% for the grains and more than 80\% for the grain boundaries. This study validates theoretical predictions and highlights a vital strategy for boosting ion transport in ionic solids. Overall, this novel approach establishes a new revenue for broader applications and greater enhancements of advanced functional materials in their related solid-state ionic devices, including all-solid-state lithium-ion batteries.

cond-mat.mtrl-sci↗

arXiv2025

Examining the Spin Structure of Altermagnetic Candidate MnTe Grown with Near Ideal Stoichiometry

Altermagnets are a recently-discovered class of materials with magnetic ordering that have a zero net magnetization and a momentum-dependent spin splitting in their band structure, arising from a collinear spin arrangement with alternating polarizations in the crystal lattice. The nickeline-structured manganese telluride (α-MnTe) is an attractive altermagnet candidate due to its predicted large spin splitting energy and a transition temperature near 300K. In this work, we present a thorough investigation of the spin structure of α-MnTe thin films grown by molecular beam epitaxy with very high crystal quality and low residual magnetization. The epitaxial α-MnTe films have a full-width-at-half-maximum of 0.1° as measured by x-ray-diffraction rocking curves and a root-mean-square roughness below 1 nm. Neutron diffraction measurements confirm the antiferromagnetic order in the α-MnTe film and show a Néel temperature of 307 K. Polarized neutron reflectometry detects a vanishingly small net magnetization which may be confined to the MnTe/InP interface, highlighting the near-ideal stoichiometry in the sample. In vacuo angle resolved photoemission spectroscopy reveals that the bulk band spectrum of the MnTe films is consistent with the weak altermagnetic order as theoretically predicted and observed for the high symmetry nodal plane in the center of the Brillouin zone. This study establishes optimized growth conditions for the synthesis of stoichiometric α-MnTe thin films which exhibit exceptional structural and magnetic ordering, thereby providing a robust platform for the precise characterization of their altermagnetic properties.

cond-mat.mtrl-sci↗

arXiv2025

Vacancy-induced Modification of Electronic Band Structure of LiBO$_{2}$ Material as Cathode Surface Coating of Lithium-ion Batteries

LiBO$_{2}$ is an electronic insulator and a promising surface coating for stabilizing high-voltage cathodes in lithium-ion batteries. Despite its potential, the functional mechanisms of this coating remain unclear, particularly the transport of lithium ions and electrons through LiBO$_{2}$ in the presence of lattice vacancies. This understanding is critical for the design and development of LiBO$_{2}$-based materials. In our previous work [Ziemke $\textit{et al.}$, J. Mater. Chem. A, 2025, $\textbf{13}$, 3146-3162], we used density functional theory (DFT) calculations to investigate the impact of lattice vacancies on Li-ion transport in both tetragonal (t-LBO) and monoclinic (m-LBO) polymorphs of LiBO$_{2}$, revealing that B vacancies in either polymorph enhanced lithium-ion transport. In this study, we expand on these findings by using DFT calculations to examine the effects of lattice vacancies on the electronic properties of both t-LBO and m-LBO polymorphs,focusing on the electronic band structure. Our analysis shows that B vacancies can enhance the electronic insulation of t-LBO while improving the ionic conduction of m-LBO. The combined results of our previous and current works indicate that B vacancy generation in LiBO$_{2}$ may enable t-LBO to function as a promising solid electrolyte and enhance the performance of m-LBO as a conformal cathode coating in lithium-ion batteries. Overall, generating B vacancies, such as through neutron irradiation, would offer a viable strategy to improve the functionality of LiBO$_{2}$ as a promising material for energy storage applications.

cond-mat.mtrl-sci↗

arXiv2020

Magnetic ordering and spin dynamics in $S=5/2$ staggered triangular lattice antiferromagnet Ba$_2$MnTeO$_6$

We report studies of the magnetic properties of a staggered stacked triangular lattice Ba$_2$MnTeO$_6$ using magnetic susceptibility, specific heat, neutron powder diffraction and inelastic neutron scattering measurements, as well as first principles density functional theory calculations. Neutron diffraction measurements reveal an antiferromagnetic order with a propagated vector $\textbf{\emph{k}}=(0.5, 0.5, 0)$ and N{é}el transition temperature of $T_\text{N}\approx20$ K. The dominant interaction derived from the Curie-Weiss fitting to the inverse DC susceptibility is antiferromagnetic. Through modelling the INS spectrum with the linear spin wave theory, the magnetic exchange interactions for the nearest intralayer, nearest interlayer, and next nearest interlayer are determined to be $J_1=0.27(3),J_2=0.27(3),$ and $J_3=-0.05(1)$ meV, respectively, and a small value of easy-axis anisotropy of $D_{zz}=-0.01$ meV is introduced. We derive a magnetic phase diagram that reveals that it is the competition between $J_1, J_2$, and $J_3$ that stabilizes the collinear stripe-type antiferromagnetic order.

cond-mat.str-el↗