Calculated Formation Energies Research Articles

Enhancement of electrochemical stability by molecular cation vacancies of the electrode material CH3NH3NiCl3 for lithium-ion batteries

At present, efforts are being made to find new low-cost materials for photovoltaic, optoelectronic and energy storage applications. In this regard, compounds of the halide perovskite type have been increasingly studied over the past few years. The incorporation of small cations in these compounds and their possible use in rechargeable batteries can be achieved by the electrochemical reversibility technique, where perovskites with large cations are used to obtain a new isostructural compound with smaller cations and large interstitial space or free vacancies for ionic transport. The present work studied the electrochemical reversibility of lithium-ion into CH3NH3NiCl3 (MANiCl3) active material, after the formation of MA+ vacancies or interstitial spaces, taking both experimental and theoretical approaches. The material displayed an anodic behavior and an initial capacity of discharge of ca. 170 mAhg−1 at 0.2C (0.1 mA), a full capacity retention up to the first 25 cycles of charge–discharge, and even reached a retention of up to 80 % of initial capacity at the 80th cycle. First-principles density functional theory calculations show that the shape of the crystal lattice and volume changes of all the different phases involved in the electrochemical process are tiny, at about 3 Å3 per cell. In addition, there are no appreciable elastic contributions to the energy variation during the de-lithiation/lithiation process, indicating that memory effects are not an issue. The calculated formation energies of the lithiated structures and the open circuit voltages are −2.91 eV and 1.33 V for LinMA1-nNiCl3 and −1.41 eV and 2.91 V for Li2nMA1-nNiCl3, respectively. These findings suggest that incorporating one or, at most, to two lithium atoms is favorable for the overall stability and electrochemical performance.

Microscopic damage in eutectic SnPb alloy: First-principles calculations and experiments

This study aims to comprehensively elucidate the microscopic origins of damage in eutectic SnPb alloy through atomic-scale investigations, a crucial endeavor for enhancing the alloy’s properties and furthering the development of Pb-free solders. First-principles calculations based on density functional theory (DFT) were employed to examine the mechanical constants and defect formation energies of the Pb phase, the β-Sn phase, and potential Sn/Pb eutectic phases in the SnPb alloy. The Voigt-Reuss-Hill approximation was utilized to derive the mechanical parameters of the elastically stable structure in SnPb alloy, facilitating the prediction of its mechanical properties. The defect formation energy calculations revealed a higher difficulty in forming vacancy defects in the β-Sn phase compared to the Pb phase. This discrepancy can be attributed to the stronger interactions between Sn atoms, resulting in the formation of more stable Sn-Sn bonds, thereby impeding vacancy generation in the β-Sn phase. Furthermore, the Pb phase exhibited a tendency for Sn atoms to occupy octahedral interstitial sites, whereas in the β-Sn phase, Pb atoms tended to displace neighboring Sn atoms along the [110] orientation into adjacent interstitial sites and occupy their lattice positions. Experimental observations complemented these calculation findings, demonstrating significant Sn element presence, up to 27.22 at%, in the Pb-rich phase, with notable microvoid damage primarily concentrated within this region. This observation aligns with the conclusions drawn from first-principles calculations and unveils the microscopic origins of damage in eutectic SnPb alloys.

A comprehensive investigation of alloying elements on site preferences, elastic properties and electronic structure of Mg17Al12 by first-principles calculations

The effect of elemental doping on the site preference, elastic properties and electronic structure of Mg17Al12 has been systematically investigated by first-principles calculations. And twenty-seven elements (Li, Na, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Sr, Y, Zr, Ag, Cd, In, Sn, Sb, Pb, Bi and La) are considered in this study. The calculations of substitution formation energies indicate that the alkali metal (Li), alkaline earth (Ca, Sr) and rare earth (Sc, Y, La) group elements and Ti, Zr favor to occupy Mg sites, and transition group (Fe, Co, Ni, Cu, Ag, Zn, Cd) elements and Ga, Ge, Sn, Sb prefer to occupy Al site, while Na, K, V, Cr, Mn, In, Pb and Bi are unstable in Mg17Al12 phase. Meanwhile, the results of phonon dispersion curves for the preferentially doped systems show that all doped structures are dynamically stable except for Sr, La and Sn doped systems. The elastic constants indicate that all preferential doping models are mechanically stable, and solute atoms with high bulk modulus lead to an increase in the bulk modulus of Mg17Al12 phase. Simultaneously, the calculated shear modulus/bulk modulus ratio (G/B), Poisson's ratio (v) and Cauchy's pressure (C‾12‐C‾44) indicate that the ductility of doped systems is better than Mg17Al12 alloy. All structures are elastic anisotropic, while the doping of Fe, Co and Ni reduces the degree of anisotropy of Mg17Al12 phase. Furthermore, the electronic structures show a strong hybridization between the p-orbitals of Mg and Al and the d-orbitals of alkaline earth, rare earth and Zr elements, resulting in higher structural stability. Finally, the adsorption behavior of O atom on Mg17Al12(110) surface and the structural stability, lattice constants, and elastic modulus of Mg34Al24-xZnx random solid solution alloys are investigated.

Sliding grain boundary formations and their atomic and electronic structures in 1T’-WTe2

Understanding the complexity of grain boundaries between domains is essential for controlling material properties. While grain boundaries in two-dimensional (2D) materials have revealed a few cases of unique features with chemical reactivity and electronic structures, the intriguing case of one-dimensional (1D) grain boundaries still remains relatively unexplored, in particular, for non-hexagonal structures. Here, sliding grain boundary formation in 1T’-WTe2 has been investigated at the atomic scale. We found that the grain boundary keeps W-Te zigzag atomic rows in one direction. The asymmetric 1D sliding grain boundary formations exhibited an angle of 38° relative to the W-Te zigzag atomic rows, strain near the sliding grain boundary formation, and fluctuations in the local density of states (LDOS). The electronic structure in the asymmetric 1D sliding grain boundary formation shows two-line features in LDOS mapping. The structural models under the directional constraint were constructed with two symmetry operations, sliding and 180°-rotation, which agree well with the experimental results. Calculation of formation energy for the models suggested that the grain boundary formation was formed by 180°-rotated domains meeting during their growth along with sliding. The understanding of the sliding grain boundary formation provides a promising path to chemical applications such as hydrogen evolution reactions.

Insight into structural, electronic, optoelectronic, dynamic, elastic, thermal and magnetic properties of pure and doped LiMgSb by nitrogen: Ab-initio calculations

In this work, ab-initio simulation has been conducted to explore and compare various properties, structural, electronic, optoelectronic, dynamic, elastic and magnetic of the pure bulk unit cell of LiMgSb and substituted by nitrogen (N). Herein, we have optimized the lattice parameter of the structure using the both approximations, generalized gradient approximation (GGA) and self-interaction correction (SIC), finding values of 6.9 and 6.7 Å, respectively. Additionally, the undoped system exhibits characteristics of a non-magnetic P-type semiconductor. The forbidden band of the compound is an indirect one at Γ-X points, aligning with existing literature, and measuring 0.742 eV and 0.95 eV under the GGA and SIC approximations, respectively. We have also investigated how the bandgap varies with the lattice parameter to analyze the influence of atomic interactions on the electronic band structure. Further analyses include the calculation of the energy photon wavelength and refractive index corresponding to the pure LiMgSb band gap. The electronic and dynamic stabilities of the compound have been confirmed through calculations of formation energies and phonon dispersion and total density of states. The bulk modulus, elastic constants, Debye temperature and melting temperature have been determined, indicating elastic stability of the system. Moreover, substitution doping the compound with N in different antisites positions with various concentrations has revealed ferromagnetic stability in Li1-xNxMgSb and LiMg1-xNxSb. Emphasis has been placed on the half-metallic behavior of the doped alloys, with an estimation of the Curie temperature utilizing mean field theory. Hence, the predicted compounds hold potential for multifaceted applications in spintronics and optoelectronics.

Impact of la on steel inclusions: a first-principles investigation into elastic properties and anisotropy

This study employed first-principles calculations based on density functional theory to explore the La-induced modifications in the elastic properties of inclusions at the microscopic level. Initially, through formation energy calculations, stable La2O3, La2O2S, and LaAlO3 inclusions were identified after the treatment with the rare earth element La. Subsequently, the elastic moduli and anisotropy of both the steel matrix and the inclusions were computed. The results revealed a substantial difference in the average elastic moduli between the common inclusions MnS, Al2O3 and the steel matrix, indicating their non-ductile nature. Conversely, La-modified inclusions, such as La2O2S and LaAlO3, exhibited closer average elastic moduli to the steel matrix with reduced anisotropy, mitigating stress concentration. This elucidates one of the reasons behind the enhanced fatigue performance of La-doped steel.

DFT analysis of Cs2NaBiCl6, Cs2NaBiBr6, and Cs2NaBiI6 perovskites for optoelectronic and thermoelectric applications

In this theoretical study, we examined the structural, electronic, optical, elastic, and thermoelectric properties of Cs2NaBiX6 (X = Cl, Br, I) halide double perovskites. The calculated formation energies are negative, affirming the stability of these compounds and their suitability for experimental synthesis. Our investigation has revealed the presence of strong covalent bonds within the [Bi/NaX6] clusters. The electronic properties demonstrate the indirect bandgap of 1.94, 3.15, and 3.24 eV for Cs2NaBiI6, Cs2NaBiBr6, and Cs2NaBiCl6, respectively, calculated using modified Becke-Johnson potential plus spin–orbit coupling (mBJ + SOC) approximation. In the visible spectrum, Cs2NaBiI6, Cs2NaBiBr6, and Cs2NaBiCl6 exhibit average rate transmittance of 53 %, 83 %, and 84 %, respectively. The absorption spectrum, extending from visible to ultraviolet (UV) wavelengths, reaches 25 × 104/cm in the case of the iodine-based perovskite. The thermoelectric characteristics, involving Seebeck coefficient, electrical conductivity, and power factor, demonstrate the use of these perovskites as a suitable for solar cells and solar thermal energy conversion technologies.

First‐principles calculations on LaX3 (X: Sb, Sn) as electrode material for lithium‐ion batteries

AbstractUsing first‐principle calculations, we investigate the rare‐earth intermetallic compound LaX3 (X = Sb and Sn) as a cathode material for rechargeable lithium‐ion batteries (LIBs). The calculations have been performed to look into the stability of the structure and the electronic properties of host LaX3 as well as its lithiated phases, LixLa1−xX3 (0 < x ≤ 1). In this study, we have observed a structural phase transformation of these intermetallic compounds from a cubic to a tetragonal structure upon lithiation to host structure. The ground state energy is calculated using the WIEN2k package to determine the structure stability and volume change due to lithium addition, which is further used to calculate the formation energy, open circuit voltage (OCV), and lithium‐ion storage capacity. The equilibrium structural parameters for all the phases are determined by achieving a total energy convergence of 10−4 Ry. The estimated band structure along high‐symmetry lines in the first Brillouin zone and the total as well as partial density of states demonstrate unequivocally that the addition of lithium does not change the metallic nature of these electrode materials. We have also calculated the theoretical lithium‐ion storage capacity and OCV for all the compounds. Despite a higher value for OCV larger than 5 V, many of the investigated materials could not be found suitable from a synthesis point of view due to positive formation energies. The formation energy calculation shows that LaSb3, with a 50% concentration of Li, is the most stable compound out of those investigated here. The calculated OCV for Li0.5La0.5Sb3 is 4.27 V. This is substantially higher than the value obtained up to this point for LIBs, which ranges from 3.20 to 3.65 V/cell. These improved results related to the most stable alloy (Li0.5La0.5Sb3) investigated in this work indicate that it is necessary to check the experimental feasibility of its synthesis and actual device performance.

The Crystal Structure of Al4SiC4 Revisited.

Al4SiC4 is a ternary wide-band-gap semiconductor with a high strength-to-weight ratio and excellent oxidation resistance. It consists of slabs of Al4C3 separated by SiC layers with the space group of P63mc. The space group allows Si to occupy two different 2a Wykoff sites, with previous studies reporting that Si occupies only one of the two sites, giving it an ordered structure. Another hitherto unexplored possibility is that Si can be randomly distributed on both 2a sites. In this work, we revisit the published ordered crystal structure using experimental methods and density functional theory (DFT). Al4SiC4 was synthesized by high-temperature sintering at 1800 °C from a powder mixture of Al4C3 and SiC. Neutron diffraction confirmed that Al4SiC4 crystallized with the space group of P63mc, with diffraction patterns that could be fitted to both the ordered and the disordered structures. Scanning transmission electron microscopy, however, provided clear evidence supporting the latter, with DFT calculations further confirming that it is 0.16 eV lower in energy per Al4SiC4 formula unit than the former. TEM analysis revealed Al vacancies in some of the atomic layers that can introduce p-type doping and direct band gaps of 0.7 and 1.2 eV, agreeing with our optical measurements. Finally, we propose that although the calculated formation energy of the Al vacancies is high, the vacancies are stabilized by entropy effects at the high synthesis temperature. This indicates that the cooling procedure after high-temperature synthesis can be important in determining the vacancy content and the electronic properties of Al4SiC4.

Pressure influenced electronic phase transition, mechanical, optoelectronic, and transport characteristics of double perovskite Rb2AgSbCl6: A first-principles investigation

In this work, we used density functional theory (DFT) simulations to investigate the structural, elastic, electronic, optical, and transport characteristics of pressure-induced Rb2AgSbCl6. By calculating the octahedral and the tolerance factors, the phase stability has been verified. The calculated formation energy and Gibbs free energy values have demonstrated the thermodynamic stability of the material. The outcomes of the mechanical behavior analysis revealed that the pressure-driven Rb2AgSbCl6 is mechanically stable and sustains ductility as well as anisotropy. Additionally, as the pressure is increased from 0 GPa to 100 GPa, the band gap has been reduced from 2.64 eV to 0 eV. The hydrostatic pressure of 100 GPa was the critical pressure at which the material revealed a metallic nature. The optical properties such as absorbance and optical conductivity shift towards lower energy and comparatively higher at increased pressure with minimal energy loss. The thermoelectric characteristics are examined utilizing the BoltzTraP code at different pressures. The figure of merit (ZT) value was increased from 0.76 to 0.80 with the increase in pressure at room temperature. These characteristics render pressure-influenced Rb2AgSbCl6 favorable candidates for utilization in solar cells as well as thermoelectric devices.

Pressure‐Induced Structural, Electronic, and Optical Properties of Lead‐Free NaGeX3 (X = F, Cl, Br, and I) Perovskites: First‐Principles Calculation

AbstractIn this study, the pressure‐induced structural, electronic, and optical properties of lead‐free inorganic Ge‐based perovskite materials NaGeX3 (X = F, Cl, Br, and I) through density functional theory (DFT) simulations conducted are explored with CASTEP. This research is driven by identifying perovskite materials with a tunable bandgap that are both efficient and non‐toxic for solar cell applications. The materials under consideration are found to be mechanically and thermodynamically stable, as per the Born stability criteria and formation energy calculations. This band structure analysis indicates these compounds exhibit semiconducting behavior with a tunable bandgap. Under ambient conditions, the Ge─X and Na─X bonds display covalent and ionic characteristics, respectively. Substituting halogens from F to I increases lattice parameters and a more covalent nature of the Ge─X bond. Concurrently, the bandgap narrows, transitioning from indirect (F) to direct (Cl, Br, and I). At the same time, the static dielectric constant rises, and both absorption and conductivity are significantly enhanced with a redshift in the optical spectrum. The application of tensile stress (positive pressure) increases both the lattice constant and bandgap, whereas the dielectric constant, absorption, conductivity, and reflectivity decrease. Conversely, compressive stress (negative pressure) induces the opposite effect. Pressure‐induced variations in the bandgap highlight the potential of NaGeX3 materials to significantly impact the next‐generation solar cells’ development, offering a pathway to more sustainable and efficient energy solutions.

The use of nonlocal corrections and SCAN to compute the electronic, optical and thermoelectric properties of XCuF3(X = K, Rb)

The current study is the computational investigations of flouroperovskites, KCuF3 and RbCuF3. The structural optimization has been performed and stability is proved by energy-volume optimization, formation energy calculations, elastic and mechanical criteria and positive phonon frequencies. The electronic band structures, density of states, optical constants and thermoelectric performance have been explored with the variety of density functional methods, ranges from local; Perdew Wang-Local Density Approximations, semi-local; Perdew–Burke–Ernzerhof Generalized Gradient Approximations, nonlocal; revised Vydrov-Voorhis, Van der Waals Density Functional and meta-GGA; Strongly Constrained and Appropriately Normed (SCAN) functionals. The earlier reported results in Usman et al. (2023) are lousy. The discrepancies and lack of accurate calculations ended up rather shocking results. The band gap reported to be 3.42 eV and 3.64 eV for KCuF3 and RbCuF3 with Perdew–Burke–Ernzerhof Generalized Gradient Approximation previously. These values are overestimated and had percentage difference of 20.78% and 24.76% for KCuF3 and RbCuF3 respectively. Surprisingly, the earlier reported band gap value is so overestimated that it matches with the SCAN value, 3.649eV in case of RbCuF3. The optical and thermoelectric parameters of KCuF3 are on the higher side than RbCuF3.

Ferric nitrate-induced phase transformation of Bi2O3 with ion exchange property for enhanced chloride removal from high-salinity wastewater

The bismuth oxide (Bi2O3)-based method for removing chloride (Cl−) ions has garnered considerable interest because of its superior selectivity and efficiency in removing Cl−. However, the slow release of Bi3+ poses a challenge to the effectiveness of Bi2O3. In this study, a novel chloride removal agent composed mainly of Fe3+-doped Bi5O7NO3 (BF-x) was synthesized through the phase transformation of Bi2O3 by ferric nitrate. By optimizing the Fe/Bi mass ratio to 3 %: 1 (BF-3), a remarkable Cl− removal efficiency of 86.4 % was achieved, representing a substantial improvement compared to the 31.2 % removal efficiency observed for pure Bi2O3. The investigation of the mechanism and formation energy calculation revealed the inherent instability of Bi5O7NO3 in comparison to that of Bi2O3, which facilitated the release of Bi3+ and enabled the direct formation of BiOCl precipitate through ion exchange of NO3– with Cl−. The synergistic effect of chemical precipitation and ion exchange contributes to the excellent Cl− removal performance of BF-3. The final Cl− removal product, comprised of BiOCl and FeOOH, exhibited significant photocatalytic efficacy in the decomposition of organic contaminants. This study proposes a novel strategy for designing and preparing high-efficiency Cl− removal agents.

Impurities in 4H silicon carbide: Site preference, lattice distortion, solubility, and charge transition levels

4H Silicon carbide (SiC) is widely recognized as one of the most advanced wide bandgap semiconductors used in the production of high-efficiency power electronic devices. Impurities play a crucial role in achieving the desired electrical properties in 4H-SiC, yet the understanding of impurities in this material remains limited. In this study, first-principles formation-energy calculations were employed to establish a comprehensive database of formation-energy diagrams for impurities in 4H-SiC. This database includes valuable information on site preference, lattice distortion, solubility, and charge transition levels (CTLs) of the impurities. The site preference for each impurity is closely related to factors such as the Fermi energy, chemical potential, and the impurity species itself. To assess the lattice distortion caused by each impurity, a comparison was made between the volume changes before and after doping. Moreover, the solubility of each impurity was determined using the detailed balance theory, thereby enabling a direct measure of the maximum impurity concentration achievable in the material. Based on the CTLs, the impurities in 4H-SiC were classified into four categories: n-type impurities, p-type impurities, amphoteric impurities, and non-electroactive impurities. This comprehensive property database for impurities in 4H-SiC provides valuable insights for tailoring the material properties through controlled doping, thereby ultimately leading to enhanced performance of power electronic devices.

Multi-objective global optimization approach predicted quasi-layered ternary TiOS crystals with promising photocatalytic properties

Abstract Titanium dioxide (TiO2) has attracted considerable research attentions for its promising applications in solar cells and photocatalytic devices. However, the intrinsic challenge lies in the relatively low energy conversion efficiency of TiO2, primarily attributed to the substantial band gaps (exceeding 3.0 eV) associated with its rutile and anatase phases. Leveraging multi-objective global optimization, we have identified two quasi-layered ternary Ti–O–S crystals, composed of titanium, oxygen, and sulfur. The calculations of formation energy, phonon dispersions, and thermal stability confirm the chemical, dynamical and thermal stability of these newly discovered phases. Employing the state-of-art hybrid density functional approach and many-body perturbation theory (quasiparticle GW approach and Bethe–Salpeter equation), we calculate the optical properties of both the TiOS phases. Significantly, both phases show favorable photocatalytic characteristics, featuring band gaps suitable for visible optical absorption and appropriate band alignments with water for effective charge carrier separation. Therefore, ternary compound TiOS holds the potential for achieving high-efficiency photochemical conversion, showing our multi-objective global optimization provides a new approach for novel environmental and energy materials design with multicomponent compounds.

O, P, Se, and Cl-doped monolayer MoS2: A new chapter in Co adsorption properties - An exploration based on first principles

This work uses a first-principles approach to thoroughly examine the impact of O, P, Se, and Cl doping of MoS2 on Co adsorption characteristics. Through structure optimization, formation energy calculations, differential charge analysis, and calculations of energy band structure and density of states, we find that P and Cl doping significantly enhances the adsorption capacity of Co on monolayer MoS2, while O and Se doping has a comparatively minor impact. This result reveals that P and Cl doping can significantly improve the adsorption stability of Co through the formation of stronger chemical bonding, which provides a theoretical basis for the design of 2D materials in adsorption applications.

First-principles study of binary and ternary phases in Mg-Gd-Ni alloys

Given the high demand for magnesium alloys across industries, it's crucial to enhance their performance by developing alloys with superior characteristics. The performance of magnesium alloys is closely related to the properties of the precipitated phase. However, there has been insufficient exploration of the mechanical properties of precipitated phases in Mg-Gd-Ni alloys. Hence, this paper calculates the formation energy, electronic structure, elastic modulus, and elastic anisotropy of the precipitated phase in Mg-Gd-Ni alloys using first principles. Calculations of formation energies and elastic constants demonstrate that MgGdNi4, Mg2Ni, 18R-LPSO, Mg2Gd, and 14H-LPSO possess commendable thermodynamic and mechanical stability. Elastic modulus calculations reveal a significant increase in the elastic modulus of magnesium, especially the bulk modulus, upon the addition of Gd and Ni elements, increasing from 34.5 GPa to a peak of 84.9 GPa. Furthermore, the strength increments of the corresponding precipitated alloys, calculated based on the elastic modulus, underscore MgGdNi4 as exhibiting the most significant strength increment. The elastic anisotropy of each second phase is evaluated using the elastic anisotropy factor, the three-dimensional surface, and the projection onto each two-dimensional plane. The order of elastic modulus anisotropy for shear and Young's modulus is MgGdNi4 > Mg2Ni > 18R-LPSO > Mg2Gd > 14H-LPSO. This study provides valuable data for regulating properties in magnesium alloys.

Semiconducting Characteristic of Antiferromagnetic Al4X3Mn (X = P, As and Sb) Compounds with Ab Initio Simulation Methods

This research reports the electronic characteristics of ternary aluminium-based Al4X3Mn (X=P, As and Sb) compounds for the most stable magnetic order which is A-type antiferromagnetic. The related systems are comforming 215 space number with P-43m space group which is simple cubic crystal structure. The computations in this research have been done within the framework of Density Functional Theory. The calculations utilized Perdew-Burke-Ernzerhof type correlation functionals within the meta-generalized gradient approximation. For considered four different type magnetic orders, the visualized volume-energy plots and the calculated formation energy values imply that the magnetic nature of these compositions is A-type antiferromagnetic. Besides, the investigated electronic natures in the detected stable magnetic phase of these systems are semiconductor since the band gaps were observed in their electronic band structures and density of states (Eg = 0.36 eV for Al4P3Mn, Eg = 0.33 eV for Al4As3Mn, and Eg = 0.18 eV for Al4Sb3Mn).

First principles study on the effects of Li deintercalation on the structural properties of a novel mixed transition metal cathode material LiNi0.75Mn0.125Fe0.125PO4 and investigation of its electric properties

Identifying and developing new cathode materials for Lithium-ion batteries (LIBs) that can achieve the desired balance between performance and environmental requirements is very challenging. Some of the key factors being highly considered in those searches include energy density, voltage, structural stability, cost, and abundance. In this work, ternary doped cathode material LiNi0.75Mn0.125Fe0.125PO4 was synthesized using sol gel method. The structural analysis using Rietveld refinement showed an orthorhombic structure with Pnma space group. The DFT + U calculations were investigated to study the structural and electronic properties during Li deintercalation in Li1-xNi0.75Mn0.125Fe0.125PO4 (0 ≤x ≤ 1). It was found that the material remained structurally stable throughout the deintercalation process. During deintercalation, the Li1-xNi0.75Mn0.125Fe0.125PO4 showed a semiconducting nature for x = 0 and x = 0.25, respectively with Eg = 1.75 eV and 0.57 eV. Then, the material becomes semi-metal for x = 0.5 and x = 0.75 and returns to the semiconducting behavior for x = 1 with Eg = 0.38 eV. The formation energy calculations indicated that the material formed a solid solution throughout the Li concentration range (0 ≤x≤), with values ranging from −17 eV to −1 eV. The voltage decreases from 4.7 eV to 3.4 eV during deintercalation. The Nyquist plot showed the presence of different relaxation processes for LiNi0.75Mn0.125Fe0.125PO4 material. A semiconducting behavior was confirmed. The ac-conductivity as a function of frequency follows the double Jonscher power law. A low dissipation factor was observed, which also decreased with frequency. This shows that LiNi0.75Mn0.125Fe0.125PO4 material could be a good cathode for LIBs.

Dual-Emission Origins in Bi3+-Doped M2O3 Sesquioxides (M = Sc, Y, Gd and Lu): A First-Principles Study.

Bi3+-doped sesquioxides exhibit dual emissions, marked by distinct Stokes shift and bandwidth, meaning unraveling their underlying origins is particularly intriguing. In this study, we employ first-principles calculations to investigate the luminescence mechanisms within the M2O3:Bi3+ (M = Sc, Y, Gd, Lu) series, with the goal of addressing the posed inquiry. Our investigation commences with the analysis of the site occupancy and charge state of bismuth ions in the two cationic sites through formation energy calculations. Additionally, we examine the local coordination environments for various excited states of Bi3+ dopants, including the 3P0,1 state and two types of charge transfer states, by evaluating their equilibrium geometric structures. The utilization of the hybrid functional enables us to obtain results of electronic structures and optical properties comparable with experiments. Importantly, the calculated energies for the 6s-6p transitions of Bi3+ dopants in the M2O3 series align well with the observed dual-emission energies. This alignment challenges the conventional spectroscopic sense that emission bands with large Stokes shifts can be exclusively ascribed to charge transfer transitions. Consequently, the integration of experimental and theoretical approaches emerges as the optimal strategy for designing novel Bi3+-doped phosphors.