Optimized Lattice Constants Research Articles

A DFT study of physical properties of the double halide perovskite Cs2AgBiCl6 under strain effects

ABSTRACT The structural, electronic, optical and thermodynamic properties of the halide perovskite material Cs2AgBiCl6 have been investigated using the density functional theory (DFT) method. As a first step, the structural properties of Cs2AgBiCl6 were examined to determine an optimized lattice constant, which was then used to calculate other physical properties. Analysis of the electronic band structure reveals that Cs2AgBiCl6 exhibits semiconductor characteristics. Optical properties, in particular the refractive index, have been investigated in the 1–3 eV energy range, corresponding to the bandgap region of the material. In addition, thermodynamic properties were analyzed using the quasi-harmonic Debye model over a temperature range of 0–600 K and a pressure range of 0–8 GPa. It was found that the Debye temperature decreases with increasing temperature but increases with increasing pressure.

The electronic and optical properties of group III-V semiconductors: Arsenides and antimonides

Investigating the structural, electronic, and optical properties of zinc-blende III-V semiconductors, particularly arsenides, and antimonides, which are crucial for optoelectronic devices such as transistors, infrared detectors, and quantum technologies due to their wide range of direct bandgaps. In this work, we have employed a first-principles approach integrating G0W0 with the HSE06 hybrid functional and spin–orbit coupling (SOC) to study their fundamental properties. Traditional Density Functional Theory (DFT) methods, particularly those using Generalized Gradient Approximation (GGA) PBE functionals, tend to underestimate bandgaps, leading to discrepancies with experimental results. To address this, our study corrects the bandgap underestimation and refines the calculation of optical constants, including the dielectric function, refractive index, extinction coefficient, and absorption coefficient. Moreover, the optimized lattice constants and electronic properties derived from our computational model strongly correlate with experimental data, demonstrating the model’s reliability in predicting material properties. The findings suggest that our methods can be applied to arsenides and antimonides, offering a pathway to designing materials with optoelectronic properties involving III-V compounds and their complex heterostructures for advanced device applications.

Exploring the structural, electronic, mechanical, magnetic and optical properties of Cs-based hydride-perovskites CsXH3 (X = Cr, Mn) for hydrogen storage application

Low cast hydride-perovskites are more efficient in power conversion and for energy storage. Here in, structural investigation, electronic, mechanical and optical properties of hydrogen based CsXH3 (X = Cr, Mn) compounds using the density functional theory. The result shows that both materials crystallize into cubic structure. The thermodynamic and dynamic stabilities are conformed through formation energy and phonon dispersion curve. The optimized lattice constants are 3.52 Å and 3.54 Å for CsCrH3 and CsMnH3 respectively. Both materials are found to be half metallic in nature. IR-Elast package are used to obtain elastic constants. The elastic study presents that both materials are ductile and have anisotropic nature. The optical parameters are studied in the range of 0–10 eV. The optical results show that both materials have an excellent optical absorption. The values obtained of gravimetric hydrogen storage capacity for these compounds are 1.55 % and 1.58 % for CsMnH3 and CsCrH3 respectively indicating that these materials can be an excellent candidate for hydrogen energy storage.

First-Principles insights to probe structural and opto-electronic properties of [formula omitted] (Y=Mg, Sr) halide perovskites with variety of DFT methods

This study reports the structural, electronic, optical, phonon, thermodynamic and thermoelectric properties of AgYF3 (X=Mg, Sr) for photovoltaic and energy applications. We performed first principles calculations using full potential linearized augmented plane wave, FP-LAPW method implemented in Wien2k. The generalized gradient approximations of Perdew–Burke–Ernzerhof PBE-GGA, and PBE revised for solids, PBEsol, is employed for structural optimization of these lead free halide perovskites. The Birch–Murnaghan energy volume curve fitting comprehend the structural stability. The optimized lattice constant of AgMgF3 and AgSrF3 obtained with PBE-GGA(PBEsol) is 3.99(3.92)Å and 4.42(4.65)Å. The stability is further tested with the help of formation energy and positive phonon dispersion curves calculations. For the calculations of explicit electronic and optical properties, we also employed Tran–Blaha modified Beck–Johnson (TB-mBJ) and Strongly Constrained but Appropriately Normed, SCAN, exchange and correlations functionals. The electronic band gap of AgMgF3 computed with PBEsol, TB-mBJ and SCAN is 1.96 eV, 5.25 eV and 2.59 eV exhibiting M-Γ indirect band gap. The band gap energy of AgSrF3 is 2.06 eV, 6.42 eV and 2.70 eV with PBEsol, TB-mBJ and SCAN. The indirect band gap nature of AgSrF3 is confirmed by PBEsol and TB-mBJ while it anticipated direct band gap behavior with meta-GGA SCAN. The different optical parameters like dielectric constant, optical conductivity, energy loss function, absorption, reflectivity and refractive index are calculated to assess optical activity of both perovskites. Comprehensive electronic and optical analysis advocates the utility of AgMgF3 and AgSrF3 for different applications is solar technology and optoelectronic devices.

Density functional analysis of structural, mechanical, electronic, and hydrogen storage properties of thermodynamically stable lead-free hydrides [formula omitted](X = Cs, Fr): A perspective of clean energy and fuel

A density functional theory based calculations are performed to investigate structural, hydrogen storage, mechanical, electronic and thermodynamical properties of lead-free hydride perovskites XGeH3 (X=Cs, Fr). The optimized lattice constant and hence volume against the minimum energy is obtained and found to be 4.176 Å and 4.184 Å for CsGeH3 and FrGeH3 respectively. The gravimetric and volumetric hydrogen storage capacity of 1.43% and 1.00%, 72.81(g.H2/L) and 73.21(g.H2/L) for CsGeH3 and FrGeH3 respectively. The density of states and electronic band structure predicted the metallic nature of both hydrides which was affirmed by the Fermi Surfaces. The calculation of Poisson’s, Pugh’s ratio and Cauchy’s pressure suggested their brittle nature. The Debye temperature decreases with the increase of temperature while volume and entropy increase by increasing applied temperature. The present study shows the potential of lead-free hydride perovskites in hydrogen storage applications due to rather suitable gravimetric hydrogen capacity and high stability.

A DFT study to explore structural, elastic, mechanical, electronic and optical properties of inverse perovskite SbPMg3 for solar cell applications

This study presents the structural, mechanical and optoelectronic properties of inverse perovskite SbPMg3 for optoelectronic applications. The structural optimization is carried out by employing Generalized Gradient Approximation of Wu–Cohen, Perdew–Burke–Ernzerhof and PBE revised for solids. The optimized lattice constant and bulk modulus of SbPMg3 is 4.85 Å and 54.20 GPa with WC-GGA scheme. The positive phonon frequencies are indicating that SbPMg3 is dynamically stable. The mechanical properties were calculated by obtaining elastic constants C11, C12 and C44. The structural stability is evaluated according to Born–Huang stability criteria. The band gap, static dielectric constant and static refractive index is 1.70 eV, 8.23 and 2.87 calculated with WC-mBJ exchange and correlation functional. The band structures show that inverse perovskite SbPMg3 possesses direct band gap nature. The absorption peaks in visible and ultraviolet energy region anticipates that SbPMg3 is promising novel material for optoelectronic applications.

A DFT study to explore structural, elastic, mechanical, phonon, electronic and optical properties of halide perovskites AgXF3(X=Be,Ca)$$ {\mathrm{AgXF}}_3\left(\mathrm{X}=\mathrm{Be},\mathrm{Ca}\right) $$ with PBEsol, TB‐mBJ and SCAN functionals

AbstractFirst principles calculations have been performed using full potential linearized augmented plane wave, FP‐LAPW, within Wien2k to elucidate structural, elastic, mechanical, phonon, electronic and optical properties of lead free halide perovskites . The energy volume curve fitting is used to examine structural stability. For structural optimization and mechanical properties, we employed Perdew–Burke–Ernzerhof generalized gradient approximation and PBEsol, revised for solids, exchange and correlation functional. The optimized lattice constant of and is 3.631 and 4.349Å. The elastic constant , and are computed to extract different mechanical parameters like Poisson's ratio, Pugh's ratio, bulk modulus, shear modulus, Young's modulus, anisotropic ratio, Cauchy pressure and shear constant. The mechanical parameters exhibit greater structural, mechanical and dynamical stability of than . The electronic and optical properties are calculated by using TB‐mBJ and SCAN potentials in addition to PBEsol. The electronic band gap of and is 4.71 and 6.01 eV with TB‐mBJ and both perovskites are indirect band gap materials. The optical response of these perovskites against wide range of incident electromagnetic radiation is assessed by calculating absorption, reflection, optical conductivity, dielectric constant, energy loss function and refraction. Strong absorption, high optical conductivity and low reflectivity indicates that and are promising materials for photovoltaic applications.

Theoretical prediction of perovskite ARH3 (A = K, Li, Rb; R[dbnd]Ca, Sr) hydride materials for hydrogen storage applications: A DFT investigation

Hydrogen (H2) storage has attracted the greatest attention in the contemporary day because of the shortage of fuel. The water splitting is considered less cost-effective and lead-free energy production by the photocatalytic process to produce hydrogen as a fuel for vehicles, petroleum refining, Pharmaceuticals, and glass purification. Perovskite materials play a vital role in H2 storage and production applications. The density functional theory (DFT) using the CASTEP code is used to study the various structural, electrical, optical, mechanical, and hydrogen (H2) capacity properties of ARH3 (A = K, Li, Rb; RSr, Ca) compounds. The compounds under investigations are optimized in the cubic structure; for ARH3 (A = K, Li, Rb; RSr, Ca), the optimized lattice constants are 3.924, 4.302, 4.559, 4.817, 4.647, and 4.884 Å, respectively. Since these hydrides are thermally stable, their formation energy is exhibited negative values. ARH3 may find usage in H2 storage applications due to its high gravimetric H2 storage densities (6.042 and 3.678 wt% for LiCaH3 and KCaH3, respectively). Furthermore, band gaps of 2.71, 2.38, 3.27, 2.73, 1.85, and 2.83 eV for ARH3 (A = K, Li, Rb; RCa, Sr) respectively, confirm the semiconductor behavior. These substances satisfy born stability criteria due to its mechanical parameters which derived from elastic constant values such as Pugh's ratio and modulus. Additionally, Pugh's ratio and Cauchy pressure demonstrate that, in contrast to other compounds, the KCaH3 compound has a ductile character (0.29). According to our analyses, studied compounds are observed a potential candidate for hydrogen storage devices.

Novel vacancy-ordered RbKGeCl6 and RbKGeBr6 double perovskites for optoelectronic and thermoelectric applications: an ab-initio DFT study

The present study examines the key characteristics of new vacancy-ordered halide double perovskites, RbKGeCl6 and RbKGeBr6, encompassing the elastic, structural, mechanical, optoelectronic, and thermoelectric properties. The Density Functional Theory (DFT) was employed to perform the calculation of the properties, facilitating the evaluation of their potential applications in optoelectronic and thermoelectric devices. The DFT calculation was conducted using the Quantum Espresso package alongside the thermo_pw tool and the BoltzTraP codes. The results revealed that the two proposed compounds possess both chemical and mechanical stability with optimized lattice constants recorded at 10.14 Å and 10.72 Å for RbKGeCl6 and RbKGeBr6, respectively. The evaluation of the elastic properties of the materials suggested reasonably high mechanical moduli of the materials. Based on the calculated electronic properties, the materials are classified as direct gap semiconductors, with energy gap values of 2.11 eV for RbKGeCl6 and 0.80 eV for RbKGeBr6 using the GGA-PBE functional. Furthermore, the use of the SCAN approximation yields more reliable energy gap of 2.51 eV and 1.08 eV for the respective compounds. The materials exhibited a high absorption coefficient and a significantly low reflectivity within the visible-ultraviolet energy spectrum. These findings strongly suggest the promising properties of the materials under study for optoelectronic applications. Furthermore, the calculated thermoelectric properties of the materials, particularly the figure of merit, revealed the materials’ potential use as thermoelectric materials. The calculated figure of merit values of RbKGeCl6 and RbKGeBr6 were found to range from 0.73 to 0.75, respectively, between 300 K and 800 K. Despite being lower, these values are comparable to those of some well-established materials including SiGe alloys (0.95), Bi2Te3 (≈0.90), and PbTe (≈0.80).

First-principles screening of XSbF3 (X = Ba and Ra) fluoroperovskites: an insight into structural, optoelectronic and thermal properties

This work presents a computational study of the physical properties such as structural, electronic, optical and thermal properties of XSbF3 (X = Ba and Ra) fluoroperovskites. The calculations were performed using the density functional theory (DFT) calculations in conjunction with Quantum Espresso code. The stability of the crystal structure XSbF3 compounds is determined by binding energy (Eb) computations. The Eb values for BaSbF3 and RaSbF3 compounds are −19.25 and −20.04eV respectively, indicating that both studied compounds are stable. The optimized lattice constants for BaSbF3 and RaSbF3 compounds are 5.03 and 5.06 Å, respectively. The evaluation of electronic properties is conducted by electronic band structure, total density of states (DOS), and partial density of states (PDOS). It is observed from the PDOS plots that the p-states of Sb and F whereas the d-states of X atoms have the major contribution in the formation of the band structure. Various optical properties have been computed and compared. The static value of ε10 highlights the metallic nature of the studied compounds while RaSbF3 stands out for having the highest recorded value of ε20. The maximum nω values for BaSbF3 and RaSbF3 are 8.46 and 6.86 respectively indicating their potential for photoelectric applications. Furthermore when examining the properties it is evident that the BaSbF3 compound stands out as a material for energy storage because of its higher electron energy at 2.36 KJ/N.mol and lower electron free energy of −2.55 KJ/N.mol compared to the RaSbF3 compound. On the other hand, the RaSbF3 compound is an efficient material for catalysis due to its high ability to absorb heat energy from the external source, as compared to the BaSbF3 compound. This study is the first computational investigation of XSbF3 (X is Ba and Ra) compounds, which provides valuable insights into the physical properties of sb-based fluroperovskites and their potential applications.

First-principles prediction of antimony based XSbF3 (X = Be, Mg, Ca and Sr) fluoroperovskites: An insight into structural, optoelectronic and thermal properties

First-principles computations have been carried out to explore the structural, optoelectronic and thermodynamic characteristics of antimony-based fluoroperovskites XSbF3 (X = Be, Mg, Ca, Sr) compounds. The optimized lattice constants of 4.46, 4.60, 4.72 and 4.81 Å are obtained for BeSbF3, MgSbF3, CaSbF3 and SrSbF3 compounds, respectively. The negative values of the binding energy of these compounds advocate that these compounds are structurally and thermodynamically stable. The electronic properties such as band structures, density of states and partial density of states reveal the metallic character of the studied compounds. Various optical and thermal parameters have been discussed in detail. To the best of our knowledge, this is the first theoretical attempt to study the physical properties of XSbF3 (X = Be, Mg, Ca, Sr) fluoroperovskite compounds. The findings of this study yield useful insights into the potential implementation of these compounds for the development of lenses, anti-reflection coatings and other valuable optoelectronic devices.

Predicting structural, elastic, and optoelectronic properties of oxide perovskites HfXO3 (X =Be, Mg) employing the DFT approach

This study conducts a comprehensive exploration of the structural, electronic, elastic, and optical properties of HfXO3 (X=Be, Mg) perovskite compounds, employing density functional theory (DFT) within the WIEN2k code. Employing the Birch Murnaghan fitting technique, our structural evaluation establishes the structural stability of these materials, with optimized lattice constants underscoring their stability at specific values. By harnessing the capabilities of the IRelast software, we have determined elastic constants and characterized the anisotropic tendencies, disclosing that both compounds exhibit a pronounced degree of anisotropy. Moreover, an in-depth investigation into electronic attributes, facilitated by the modified Becke–Johnson potential, uncovers these materials as indirect narrow band gap semiconductors, with calculated band gaps of 1.14 eV for HfBeO3 and 0.8 eV for HfMgO3 serving as vital indicators of their electronic character. Furthermore, we delve into the optical traits of these materials, revealing their photon transparency within the energy spectrum of 0 eV to 15 eV. These key optical properties encompass dielectric functions, refractive index, optical conductivity, absorption coefficient, extinction coefficient, energy loss function, and reflectivity. This comprehensive exploration offers a holistic understanding of the optical behaviors exhibited by these materials. By skillfully combining structural, electronic, elastic, and optical analyses, this study significantly contributes to the comprehension of HfXO3 (X=Be, Mg) perovskites, forging a path for their potential applications and serving as a foundation for future research endeavors.

Novel ternary halide perovskite AMX3(A/M=Li, Na, K, Rb, Be, Mg, Ca, Sr, Ba, X=Br, Cl, F, I) for optoelectronic applications

In this article, we present the first principle calculations on 40 AMX3 perovskite compounds - AMX3 composition, where X = Br, Cl, F or I, and M = an alkali or alkali-earth elements. These compounds are not reported until now either theoretically or experimentally. From the literature reports of ANN, the structures were relaxed for minimum energy, and the optimized lattice constants were used to perform calculations for GGA_PBE. In this work, apart from the novel AMX3 compound's structural and electronic property investigation, we are interested in studying the impact of spin and orbital angular momentum of electrons over these AMX3 materials. So, SOC and TB_mBJ have been included in this work. The results of volume optimization, i.e., bulk modulus, pressure derivative, volume, and total energy, are tabulated. The four cases of study GGA_PBE, GGA_PBE+SOC, GGA_PBE+TB_mBJ, and GGA_PBE+SOC+TB_mBJ are compared for all the 40 compounds. The trends the band gap exhibits are studied for halides, alkalis, and alkali-earth elements. Among the compounds, the band gap of seven of the compounds studied in this work matches approximately with the Schockley-Queisser limit(Eg≈1.34 eV). The compounds presented and discussed in this article can potentially contribute to advancements in solar cell and semiconductor research.

Investigating the structural, electronic, magnetic, thermodynamic, and optical properties of rare earth-based halide perovskites CsMCl3 (M = U, Np, Pu)

A detailed study of the physical properties of caesium-based halide perovskites, specifically CsUCl3, CsNpCl3, and CsPuCl3, by full-potential linearized augmented plane wave method has been performed. The stability of the compounds is ensured after energy optimization in two different phases, viz. ferromagnetic and non–magnetic, wherefrom we concluded these perovskites are energetically more stable in the ferromagnetic phase. By adopting the optimized lattice constant, we have determined different electronic, magnetic, thermodynamic, optical, and transport properties. The GGA+ mBJ approximation predicts the half-metallic character of these compounds. The M-sited atom is the foremost contributor to the ferromagnetic nature of these compounds. We have also calculated thermodynamic parameters like thermal expansion, Gruneisen parameter, specific heat capacity, and Debye temperature by employing the quasi-harmonic Debye model. Further optical properties of the compounds are examined in terms of dielectric constant, absorption coefficient, and refractive index. The obtained results from the study signify that these materials are apt for electro-optic and spintronics devices.

Optoelectronic and thermoelectric properties of novel stable lead-free cubic double perovskites A2NaIO6 (A = Ca, Sr) for renewable energy applications.

Over the past decade, perovskites have received considerable attention because of their record power conversion efficiency (25.7%) in solar cells. These materials have also received recent research interest in thermoelectrics, most likely due to their high carrier mobility, large power factor, and ultralow thermal conductivity. Therefore, in the present work, we have examined the optoelectronic and thermoelectric properties of A2NaIO6 (A = Ca, Sr) double perovskites using first-principles calculations. Stability has been confirmed using reliable and accurate descriptors of formation energy and phonon calculations. The optimized lattice constant and volume show an increasing tendency with changing A site cation (Ca → Sr). The computed band structures depict the semiconducting nature with direct band gap values of 2.64 eV (Ca2NaIO6) and 2.48 eV (Sr2NaIO6). The absorption was found to start in the visible range where the reflectivity was less than 10%. Moreover, the high Seebeck coefficient, large electrical conductivity, and fairly low thermal conductivity result in ZT values of 0.724 for Ca2NaIO6 and 0.686 for Sr2NaIO6 at 1000 K. With their optimum band gap, excellent light absorption capacity, and high ZT values, A2NaIO6 emerge as promising candidates for optoelectronic and thermoelectric applications.

Ab Initio Calculations of Structural, Lattice Dynamical, and Thermodynamic Properties of Zinc‐Blende HgSe and CdSe

The structural, dynamical, and thermodynamic properties of zinc‐blende (ZB) mercury selenide (HgSe) and cadmium selenide (CdSe) were systematically explored using an ab initio pseudopotential approach based on the density functional theory (DFT). The optimized lattice constants are in excellent agreement with the available experimental and theoretical results. The electronic properties show semiconducting behavior with a direct bandgap of 0 and 0.36 eV for HgSe and CdSe, respectively. Also, using the linear response approach, the detailed vibration properties of HgSe and CdSe are obtained. According to the calculated phonon dispersion, it is concluded that HgSe and CdSe are dynamically stable in the ground state; several peculiarities in the dispersion curves of these materials are generally similar, but the zone‐boundary frequencies and zone‐center optical frequencies of HgSe are lower than those of CdSe. The phonon frequencies at the high‐symmetry points Γ, X, and L for HgSe and CdSe are in good agreement with the other theoretical reported. On the other hand, the dielectric properties are investigated and discussed. The results show that the dielectric tensor is diagonal, and the Born effective charge tensor is also isotropic. Finally, based on the lattice dynamical properties, we investigate the thermodynamic properties of both compounds, such as Helmholtz free energy F, internal energy E, entropy S, and specific heat Cv. The results show that HgSe and CdSe exhibit similar but slightly different behaviors in terms of its thermodynamic properties, which is expected because the atoms Hg and Cd are in the same group and exhibit a different atom mass. Most of the results presented in this study are novel and should provide a useful reference for future studies.

The Electronic, Optical, and Mechanical Properties of Quasi-One-Dimensional Molybdenum Sesquisulfide Mo2S3: A Density Functional Theory Study

In this work, a study on structural, electronic, optical, and mechanical properties of monoclinic-type Mo2S3 (space group P21/M) has been examined. Optimized lattice constants of [Formula: see text][Formula: see text]Å, [Formula: see text][Formula: see text]Å, [Formula: see text][Formula: see text]Å and bond angles of [Formula: see text], [Formula: see text] have been calculated, and it appears that they are in close match to other theoretical and experimental data. Our bandstructure and density of states confirm the metallic properties of the molybdenum sesquisulfide, which also agrees well with other theoretical data. Importantly, the electron orbitals found in conduction (valence) bands can provide an explanation of covalent Mo–Mo (Mo–S) bonding inside the Mo2S3 lattice. For optical properties, a high absorption coefficient of [Formula: see text] has been obtained, suitable for applications within the vacuum ultraviolet (VUV) range. Our high reflectivity calculation suggests the use of metallic coating on other materials to reflect light. For mechanical properties, our elastic data also confirm the material’s stability mechanically, identifying it as covalent, anisotropic, and brittle. The micro-machinability parameter calculated further suggests that such material could be used as lubricants or oils for applications in mechanical engineering.

Structural, optoelectronic and thermodynamical insights into 2H-ZrO2: A DFT investigation

The monolayer transition metal dichalcogenides have appeared to be an intriguing area of ongoing research in two-dimensional materials. In this study, we have investigated the structural, lattice dynamic, optoelectronic and thermodynamic properties of 2H-ZrO2 monolayer using first-principle calculations. The negative value of cohesive energy (-0.42 eV) manifests that 2H-ZrO2 is structurally stable and can be fabricated experimentally. The optimized lattice constant is found to be 3.15 Å. Lattice dynamic stability is assessed by the phonon dispersion curves and phonon density of states, which indicating that 2H-ZrO2 monolayer is dynamic stable. In order to analyze the thermal stability of 2H-ZrO2, we have computed thermodynamic properties within the range of 0–1000 K. The negative values of free energy indicate the thermal stability of the monolayer. Various electronic parameters such as density of states, partial density of states and electronic band structure have been obtained. It is found that 2H-ZrO2 is a p-type semiconductor, which possesses an indirect bandgap of 1.58 eV between valence and conduction bands. A number of in-plane and out-of-plane optical spectra have been discussed in detail. This study suggested that monolayer 2H-ZrO2 is a suitable candidate for energy related applications and may aid in the creation of effective optoelectronic devices.

Site occupancy and electronic properties of NbCo2 Laves phases doped with Re

In the present work, we have carried out an extensive first-principles study of Re doped C14, C15 and C36 type NbCo2 Laves phases, respectively. The geometric optimized lattice constants of Laves phases decrease as Re replaces Nb site, while increase as Re replaces Co site. The binding energy and the formation energy indicate that Re will promote the formation of Laves phases. The results of electronic properties (density of states and charge density difference) reveal that Re has a strong bond with its NN (nearest neighborhood) Co and NN Nb atoms, which were mainly attributed to the d-d hybridization. Besides, as Re doping Co site, the increase of charge density between Re and its NN atoms indicates that Re prefers to occupy the Co site.

High-performance ε-VOPO4 cathode materials for sodium ion battery applications

The nanoscale ε-VOPO4 materials were successfully prepared by hydrothermal synthesis of H2VOPO4 precursors and further calcination. XRD and AFM characterization showed that the prepared nano-ε-VOPO4 belonged to monoclinic crystalline system with high purity of physical phase and an average particle size of 150 nm. FT-IR spectroscopy showed that the characteristic peak of the H2VOPO4 precursor (at 797 cm−1) disappeared after calcination and a characteristic peak representing ε-VOPO4 was captured at 914 cm−1. Furthermore, the XPS results showed that the V in the prepared ε-VOPO4 was mainly +5 valence. In order to further evaluate the potential of ε-VOPO4 as an energy storage material, it was applied as cathode material in sodium ion battery system. Electrochemical tests have demonstrated that ε-VOPO4 has satisfactory electrochemical performance as cathode material for sodium ion batteries. The initial capacities of ε-VOPO4 electrode materials reached 162.3, 135.1, 86.7, 51.4, and 29.7 mAh g−1 at 0.05, 0.2, 1, 2, and 5 C, respectively, and the long-cycle performance results showed that the electrochemical stability was still superior after 200 cycles at a current density of 0.5 C. Meanwhile, the density functional theory calculation shows that the optimized lattice constants (a = 7.279 Å, b = 6.896 Å and c = 7.268 Å) are in good agreement with the experimental data. Notably, the experimental ε-VOPO4 material has a higher voltage plateau than the theoretical calculation, which shows the potential advantage of ε-VOPO4 as a new generation electrode material for high energy storage systems.