Pristine Phase Research Articles

First-principles study of the electronic structure, Z2 invariant, and quantum oscillation in the kagome material CsV3Sb5

This work presents a detailed study of the electronic structure, phonon dispersion, Z2 invariant calculation, and Fermi surface of the newly discovered kagome superconductor CsV3Sb5, using density functional theory. The phonon dispersion in the pristine state reveals two negative modes at the M and L points of the Brillouin zone, indicating lattice instability. CsV3Sb5 transitions into a structurally stable 2 × 2 × 1 charge density wave (CDW) phase, confirmed by positive phonon modes. The electronic band structure shows several Dirac points near the Fermi level, with a narrow gap opening due to spin–orbit coupling (SOC), although the effect of SOC on other bands is minimal. In the pristine phase, this material exhibits a quasi-2D cylindrical Fermi surface, which undergoes reconstruction in the CDW phase. We calculated quantum oscillation frequencies using Onsager’s relation, finding good agreement with experimental results in the CDW phase. To explore the topological properties of CsV3Sb5, we computed the Z2 invariant in both pristine and CDW phases, resulting in a value of (ν0; ν1ν2ν3) = (1; 000), suggesting the strong topological nature of this material. Our detailed analysis of phonon dispersion, electronic bands, Fermi surface mapping, and Z2 invariant provides insights into the topological properties, CDW order, and unconventional superconductivity in AV3Sb5 (A = K, Rb, and Cs).

Origin of competing charge density waves in kagome metal ScV6Sn6

Understanding competing charge density wave (CDW) orders in the bilayer kagome metal ScV6Sn6 remains challenging. Experimentally, upon cooling, short-range order with wave vector q2=(13,13,12)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{{{\\bf{q}}}}}_{2}=(\\frac{1}{3},\\frac{1}{3},\\frac{1}{2})$$\\end{document} forms, which is subsequently suppressed by the condensation of long-range q3=(13,13,13)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{{{\\bf{q}}}}}_{3}=(\\frac{1}{3},\\frac{1}{3},\\frac{1}{3})$$\\end{document} CDW order at lower temperature. Theoretically, however, the q2 CDW is predicted as the ground state, leaving the CDW mechanism elusive. Here, using anharmonic phonon-phonon calculations combined with density functional theory, we predict a temperature-driven structural phase transitions from the high-temperature pristine phase to the q2 CDW, followed by the low-temperature q3 CDW, explaining experimental observations. We demonstrate that semi-core electron states stabilize the q3 CDW over the q2 CDW. Furthermore, we find that the out-of-plane lattice parameter controls the competing CDWs, motivating us to propose compressive bi-axial strain as an experimental protocol to stabilize the q2 CDW. Finally, we suggest Ge or Pb doping at the Sn site as another potential avenue to control CDW instabilities. Our work provides a full theory of CDWs in ScV6Sn6, rationalizing experimental observations and resolving earlier discrepancies between theory and experiment.

Antithermal-Quenching All-Inorganic Perovskite Crystals with Green Ultralong Persistent Luminescence for Advanced Anticounterfeiting Applications.

Long persistent luminescence (PersL) materials have revolutionized many fields of optoelectronics and photonics due to their applications in anticounterfeiting, information encryption, and in vivo bioimaging. Here, we reported a novel PersL crystal prepared by the heterovalent doping of Sb3+ into perovskite tetragonal phase RbCdCl3, comparing with the pristine non-perovskite orthorhombic phase analogue without PersL property. Surprisingly, under the UV light irradiation, the title crystals concurrently exhibit green ultralong PersL (>2400 s), high photoluminescence quantum yield (49.1%), and antithermal quenching in the range from 148 to 328 K. It was revealed by experimental results and theoretical analyses that green ultralong PersL and antithermal quenching of perovskite-phase RbCdCl3/Sb3+ crystals originate from the electron transition between the 5s2 level of the dopant Sb3+ and the electronic defect-induced trap states. Enlightened by the excellent optical properties, the tetragonal perovskite-phase RbCdCl3/Sb3+ PersL materials show promising application prospects in anticounterfeiting and encryption of information.

Significantly Enhanced Thermoelectric Performance of p-Type Mg3Sb2 via Zn Substitution on Mg(2) Site: Optimization of Hole Concentration Through Ag Doping.

n-Type Mg3Sb2-based thermoelectric materials have recently garnered significant interest due to their superior thermoelectric efficiency. Yet, the advancement of p-type Mg3Sb2 for thermoelectric applications is impeded by its lower dimensionless figure of merit (zT). In this study, we demonstrate the improved thermoelectric performance of p-type Mg3Sb2 through the strategic optimization of Zn content and Ag doping on the Mg/Zn(2) site. Initially, samples of Mg3-xZnxSb2 (x = 0, 0.5, 1.0, and 1.5) were synthesized via elemental reactions within a Pyrex tube, followed by densification through hot pressing. X-ray diffraction analysis confirmed that the Mg3-xZnxSb2 phases retain the same Pm1 space group as the pristine Mg3Sb2 phase. The strategic substitution of Zn improved the power factor via band convergence and reduced lattice thermal conductivity by introducing point defect phonon scattering. This led to a peak zT of 0.5 at 725 K, with an average zT of 0.25 across the 325-725 K range. Enhancement in carrier concentration was achieved by doping Ag onto the Zn site, culminating in a peak zT of 0.95 at 725 K and an average zT of 0.46 between 325 and 725 K for the Mg2Zn0.97Ag0.03Sb2 sample. This performance surpasses that of most p-type Mg3Sb2-based materials, markedly advancing the potential for Mg3Sb2-based materials in midtemperature heat recovery thermoelectric generators.

Characterizations and Energy Analysis of Hydroxyl Group Functionalized Graphene (Nanomaterial) Mixed with Paraffin Wax (Polymer Pcm) as Thermal Energy Storage Materials And Applications

This work comprised of Paraffin wax as phase change material mixed/doped with functionalized graphene (hydroxyl group) for countering the poor thermal conductivity of the pristine phase change material. Firstly, Experiments were conducted on Thermal energy storage system during charging (melting) of the doped PCM. The main outcomes of these experiments were that as the volume concentrations of doped PCM and flow rate of the heat transfer fluid (HTF) were increased the charging time decreases along with increments in PCM temperature and accumulated energies. In case of OH functionalized graphene mixed with paraffin wax the charging time decreases by 38.4% to 84.61% for the HTF flow rate 25 ml/s over pure paraffin wax. Secondly, the advanced functional materials i.e., Paraffin wax mixed with functionalized hydroxyl group graphene was characterized by FTIR, XRD, TGA, DSC and FESEM, . The latent heat of melting obtained was 179.36 J/g for 1% graphene doping by DSC.

Photoelectromagnetic multimode triggered phase change materials for thermotherapy

AbstractNeither pristine phase change materials (PCMs) nor metal‐organic frameworks (MOFs) can be driven by optical/electrical/magnetic triggers for multiple energy conversion and thermal storage, which cannot satisfy the requirements of multi‐scenario applications. Herein, a three‐dimensional interconnected forest‐type array carbon network anchored by Co nanoparticles serving as optical/electrical/magnetic multimode triggers was developed through in situ growth of two‐dimensional MOF nanosheet arrays on pre‐carbonized melamine foam and subsequent high‐temperature carbonization. After the encapsulation of polyethylene glycol, the resulting composite PCMs simultaneously integrate fascinating photothermal, electrothermal, magnetothermal conversion and storage for personal thermotherapy. Benefiting from the synergistic enhancement of forest‐type array carbon heterostructure and Co nanoparticles, composite PCMs exhibit high thermal/electrical conduction and strong full‐spectrum absorption capacities. Resultantly, low‐energy photoelectric triggers are sufficient to drive high‐efficiency photothermal/electrothermal conversion and storage of composite PCMs (93.1%, 100 mW/cm2; 92.9%, 2.5 V). Additionally, composite PCMs also exhibit excellent encapsulation stability without liquid phase leakage, long‐term thermal reliability and multiple energy conversion and storage stability after multiple cycles. The proposed photoelectromagnetic multimode triggers are aimed to inspire innovation and accelerate major breakthroughs in advanced responsive composite PCMs toward multiple energy utilization and personal thermotherapy.

Abnormally High Graphitic Crystallization of Cellulose Nanocrystals.

Cellulose nanocrystals (CNCs) are currently of great interest for many applications, such as energy storage and nanocomposites, because of their natural abundance. A number of carbonization studies have reported abnormal graphitization behavior of CNCs, although cellulose is generally known as a precursor for hard carbon (nongraphitizable carbon). Herein, we report a spray-freeze-drying (SFD) method for CNCs and a subsequent carbonization study to ascertain the difference in the structural development between the amorphous and crystalline phases. The morphological observation by high-resolution transmission electron microscopy of the carbonized SFD-CNC clearly shows that the amorphous and crystalline phases of CNC are attributed to the formation of hard and soft carbon, respectively. The results of a reactive molecular dynamics (RMD) study also show that the amorphous cellulose phase leads to the formation of fewer carbon ring structures, indicative of hard carbon. In contrast, the pristine crystalline cellulose phase has a higher density and thermal stability, resulting in limited molecular relaxation and the formation of a highly crystalline graphitic structure (soft carbon).

Scattered Co-anchored MoS2 synergistically boosting photothermal capture and storage of phase change materials

Pristine phase change materials (PCMs) suffer from inherent deficiencies of poor solar absorption and photothermal conversion. Herein, we proposed a strategy of co-incorporation of zero-dimensional (0D) metal nanoparticles and two-dimensional (2D) photothermal materials in PCMs for efficient capture and conversion of solar energy into thermal energy. Highly scattered Co-anchored MoS2 nanoflower cluster serving as photon and phonon triggers was prepared by in-situ hydrothermal growth of ZIF67 polyhedron on 2D MoS2 and subsequent high-temperature carbonization. After encapsulating thermal storage unit (paraffin wax), the obtained composite PCMs integrated high-performance photothermal conversion and thermal energy storage capability. Benefiting from the synergistic enhancement of 0D Co nanoparticles with localized surface plasmon resonance effect, carbon layer with the conjugation effect and 2D MoS2 with strong solar absorption, composite PCMs exhibited a high photothermal conversion efficiency of 95.19%. Additionally, the resulting composite PCMs also demonstrated long-term thermal storage stability and durable structural stability after 300 thermal cycles. The proposed collaborative co-incorporation strategy provides some innovative references for developing next-generation photothermal PCMs in solar energy utilization.

Pressure-induced magnetic phase and structural transition in SmSb2

Abstract Motivated by the recent discovery of unconventional superconductivity around a magnetic quantum critical point in pressurized CeSb2, here we present a high-pressure study of an isostructural antiferromagnetic (AFM) SmSb2 through electrical transport and synchrotron x-ray diffraction measurements. At P C ~2.5 GPa, we found a pressure-induced magnetic phase transition accompanied by a Cmca→P4/nmm structural phase transition. In the pristine AFM phase below P C, the AFM transition temperature of SmSb2 is insensitive to pressure; in the emergent magnetic phase above P C, however, the magnetic critical temperature increases rapidly with increasing pressure. In addition, at ambient pressure, the magnetoresistivity (MR) of SmSb2 increases suddenly upon cooling below the AFM transition temperature and presents linear nonsaturating behavior under high field at 2 K. With increasing pressure above P C, the MR behavior remains similar to that observed at ambient pressure, both in terms of temperature- and field-dependent MR. This leads us to argue an AFM-like state for SmSb2 above P C. Within the investigated pressure of up to 45.3 GPa and the temperature of down to1.8 K, we found no signature of superconductivity in SmSb2.

Optimizing Performance in Supercapacitors through Surface Decoration of Bismuth Nanosheets.

Bismuth (Bi) exhibits a high theoretical capacity, excellent electrical conductivity properties, and remarkable interlayer spacing, making it an ideal electrode material for supercapacitors. However, during the charge and discharge processes, Bi is prone to volume expansion and pulverization, resulting in a decline in the capacitance. Deposition of a nonmetal on its surface is considered an effective way to modulate its morphology and electronic structure. Herein, we employed the chemical vapor deposition technique to fabricate Se-decorated Bi nanosheets on a nickel foam (NF) substrate. Various characterizations indicated that the deposition of Se on Bi nanosheets regulated their surface morphology and chemical state, while sustaining their pristine phase structure. Electrochemical tests demonstrated that Se-decorated Bi nanosheets exhibited a 51.1% improvement in capacity compared with pristine Bi nanosheets (1313 F/g compared to 869 F/g at a current density of 5 A/g). The energy density of the active material in an assembled asymmetric supercapacitor could reach 151.2 Wh/kg at a power density of 800 W/kg. These findings suggest that Se decoration is a promising strategy to enhance the capacity of the Bi nanosheets.

Electrical-Driven Directed-Evolution of Copper Nanowires Catalysts for Efficient Nitrate Reduction to Ammonia.

The electrocatalytic conversion of nitrate (NO3 -) to NH3 (NO3RR) at ambient conditions offers a promising alternative to the Haber-Bosch process. The pivotal factors in optimizing the proficient conversion of NO3 - into NH3 include enhancing the adsorption capabilities of the intermediates on the catalyst surface and expediting the hydrogenation steps. Herein, the Cu/Cu2O/Pi NWs catalyst is designed based on the directed-evolution strategy to achieve an efficient reduction of NO3‾. Benefiting from the synergistic effect of the OV-enriched Cu2O phase developed during the directed-evolution process and the pristine Cu phase, the catalyst exhibits improved adsorption performance for diverse NO3RR intermediates. Additionally, the phosphate group anchored on the catalyst's surface during the directed-evolution process facilitates water electrolysis, thereby generating Hads on the catalyst surface and promoting the hydrogenation step of NO3RR. As a result, the Cu/Cu2O/Pi NWs catalyst shows an excellent FE for NH3 (96.6%) and super-high NH3 yield rate of 1.2molh-1gcat. -1 in 1m KOH and 0.1m KNO3 solution at -0.5V versus RHE. Moreover, the catalyst's stability is enhanced by the stabilizing influence of the phosphate group on the Cu2O phase. This work highlights the promise of a directed-evolution approach in designing catalysts for NO3RR.

A High‐Voltage Solid State Electrolyte Based on Spinel‐Like Chloride Made of Low‐Cost and Abundant Resources

AbstractRecently, halide solid state electrolytes (SSEs) have received great attention owing to their fast ionic conductivity, high oxidation potential, and good chemical and electrochemical compatibility with high voltage cathode materials. However, most of reported halide SSEs contain rather rare and expensive elements, which hinders their sustainable utilizations in practical batteries. Here in this work, under the guidance of systematic modelling based on the density functional theory (DFT), a low‐cost alternative is developed through optimizing the lattice chemistry in a recently identified spinel‐like chloride Li2CrCl4 into Li5/3Cr1/3Zr1/3Cl4 for remarkably enhanced ionic conductivity and stable electrochemical window with respect to the Li‐anode. This new phase has then been synthesized successfully, delivering an ionic conductivity over 1200 times of that of the pristine phase Li2CrCl4, in addition to a high oxidation potential (up to 4.1 V vs Li/Li+) to enable outstanding interfacial compatibility with high voltage cathodes. Such a high‐voltage and fast Li‐ion conducting solid‐state electrolyte is expected to provide a highly desirable basis toward developing high energy‐density all solid‐state batteries (ASSBs) using economical and Earth‐rich elements.

Effect of novel fin distribution on the melting process of thermal storage units

Thermal storage units play a crucial role in storing excess energy and utilizing it when required. Enhancing the thermal performance of these units is of utmost importance for better thermal energy management. Therefore, this paper suggests introducing new fin distributions to decrease the thermal resistance of the storage unit and, thus, enhance the melting process. An octagonal tube and shell unit with nanoparticle-enhanced phase change material are suggested. Three considered fin distributions to improve the heat transfer inside the unit are straight dual-radial fins, tree-like fins, and roots-like fins. Also, since copper has high thermal conductivity, its nanoparticles are incorporated with the phase change material with different concentrations, i.e., 0, 4, and 8 vol%. The Galerkin finite element technique is employed to model the storage unit. The results show that using roots-like fins has a significant effect in reducing the phase change material melting time by 56% and 91% lower than dual-radial fins and tree-like fins, respectively. The higher nanoparticle concentration (8 vol%) can also improve the thermal storage unit performance by 28.9% compared to the pristine phase change materials. Thus, this study recommends using roots-like fins with nanoparticles in the thermal storage units to enhance thermal performance.

Evaluation of MXene Ti3C2 Charge–Discharge Behaviors as an Electrode Material for Intercalation Batteries

Eliminating A element from the MAX phases, the resulted 2D structure, named MXene, can be used as the electrode material for the intercalation, namely, Li‐ion, Na‐ion, K‐ion, and Mg‐ion batteries. MXene Ti3C2, produced by etching Ti3AlC2, is a promising intercalation electrode material, which is systematically evaluated in this article by taking data from literature. The diagrams provide a manner to assess and compare the most important characterizations, i.e., rate‐capability and performance. The evaluations show that the synthesis methods of the pristine MAX phase as well as the final MXene play vital roles on the properties. The rank of synthesis methods and also commercial pristine material is recognized and reported based on the analyzed properties. Moreover, effectiveness of the additives, dopants, compositing, nanosizing, and etching is assessed precisely. Also, comparison between different types of intercalation batteries regarding the usage of MXene as the electrode is performed. This article paves the way for future studies and evaluations of this kind of electrode materials. It guides the researchers to modify, design, and engineer their manufactured electrodes to meet higher quality of the properties.

Hydrogen production from dry reforming of methane, using CO2 previously chemisorbed in the Li6Zn1-xNixO4 solid solution

Li6ZnO4 was chemically modified by nickel addition, in order to develop different compositions of the solid solution Li6Zn1-xNixO4. These materials were evaluated bifunctionally; analyzing their CO2 capture performances, as well as on their catalytic properties for H2 production via dry reforming of methane (DRM). The crystal structures of Li6Zn1-xNixO4 solid solution samples were determined through X-ray diffraction, which confirmed the integration of nickel ions up to a concentration around 20 mol%, meanwhile beyond this value, a secondary phase was detected. These results were supported by XPS and TEM analyses. Then, dynamic and isothermal thermogravimetric analyses of CO2 capture revealed that Li6Zn1-xNixO4 solid solution samples exhibited good CO2 chemisorption efficiencies, similarly to the pristine Li6ZnO4 chemisorption trends observed. Moreover, a kinetic analysis of CO2 isothermal chemisorptions, using the Avrami-Erofeev model, evidenced an increment of the constant rates as a function of the Ni content. Since Ni2+ ions incorporation did not reduce the CO2 capture efficiency and kinetics, the catalytic properties of these materials were evaluated in the DRM process. Results demonstrated that nickel ions favored hydrogen (H2) production over the pristine Li6ZnO4 phase, despite a second H2 production reaction was determined, methane decomposition. Thereby, Li6Zn1-xNixO4 ceramics can be employed as bifunctional materials.

Structural and Electrochemical Investigation of 3D Tunnel Type Li0.44MnO2 Cathode Material for Secondary Li-Ion Batteries

The design of new cathode materials remains a key goal in the development of (post) Li-ion batteries. In that regard, densely packed structures like Li0.44MnO2 are judicious for study. The presence of Mn as a transition metal makes it more attractive due to its sustainable nature, low cost, elemental abundance, structural diversity/polymorphism, and rich oxidation states (2+ to 7+) offering tunable redox potential [1]. Here, we have investigated Mn-based tunnel-type Li0.44MnO2 oxide for secondary LIBs. i) Li44MnO2 (LMO) was prepared by a soft chemical method using the corresponding sodium manganese oxide (Na0.44MnO2) as a parent compound [2]. The crystal structure of Li0.44MnO2 maintains the parent Na0.44MnO2-type tunnel structure which is analogous to Na4Mn4Ti5O18 having an orthorhombic (s.g. Pbam) crystal system [3]. To understand redox chemistry, this material was studied for both cationic (Mn) and anionic (O) redox reactions using ex-situ X-ray photoelectron spectroscopy. The lithium (de)insertion mechanism of Li0.44MnO2 was explored involving ab initio calculations and in-situ X-ray diffraction experiments. Combined with electrochemical measurements, structural characterizations, and first principles DFT calculations revealed the capacity correlated strongly with both cationic and anionic redox reactions. ii) We have studied the phase transition of Li44MnO2 from a 3D tunnel-type structure to a cubic spinel structure by in-situ X-ray diffraction and Raman spectroscopy. The mechanism of transformation was elucidated by employing transmission electron microscopy. In this case, diffusion-less transformation occurs involving the rearrangement of atoms during heating [4]. An increase in the average redox potential from the pristine orthorhombic phase to the final spinel phase was observed by electrochemical studies. iii) Further to improve the electrochemical performance of Li0.44MnO2, Ti was used as a dopant. The Li0.44[Mn1-xTix]O2 (x=0, 0.11, 0.22, 0.33, 0.44, 0.56) series were obtained with chemical ion exchange from Na precursors. The Na precursors (Na0.44[Mn1-xTix]O2) were prepared via a simple solid-state route. Ti-substituted compositions exhibited similar crystal structures to their parent LMO i.e. orthorhombic framework with Pbam symmetry. A tunnel-type morphology was observed in all cases. The electrochemical performance of Ti-substituted LMO as cathode material for LIBs was studied in a half-cell configuration. The structure and electrochemical properties of Ti-doped LMO, reaching the highest capacity of 128 mAh/g, will be described. Keywords: batteries; cathode; tunnel type manganese oxides; phase transformation; doping

Significant strength enhancement of high-entropy alloy via phase engineering and lattice distortion

The extraordinary mechanical properties of high-entropy alloys (HEAs) hold great promise for their applications under extreme conditions (high pressure, high temperature, etc.). However, investigations on the mechanical properties of HEAs under extreme conditions (especially at high pressures) are extremely scarce, preventing their future applications. In this study, significant strength enhancement of Cantor (CoCrFeMnNi) HEA is achieved via phase engineering by using high-pressure techniques. The pressure-induced fcc-hcp phase transition of Cantor HEA leads to a strength increase of 65 % across the phase transition. Consequently, the hcp-Cantor HEA behaves as strongly as typical superhard ceramic B4C and surpasses corundum at moderate pressures. Moreover, the hcp-Cantor HEA quenched to ambient pressure is 47 % harder than the pristine fcc phase. In addition, by substituting the Mn atom with the Pd atom to introduce a severe lattice distortion in Cantor HEA, the CoCrFePdNi HEA turns out to be almost twice harder than Cantor HEAs at ambient pressure. The excellent mechanical properties of HEAs promise their potential applications at high pressures. These results also demonstrate that phase engineering and the introduction of severe lattice distortion represent two promising methods of developing high-strength HEAs in the future.

In situ insight into temperature-dependent microstructure evolution of carbon doped phase change materials

Carbon-doped Ge2Sb2Te5 (CGST) is a potential candidate in phase change random access memory (PCRAM) with superb thermal stability and ultrahigh cycle endurance. Direct observation of the microstructure evolution of CGST is desirable to uncover the phase transformation mechanism on the relationship of nucleation/crystalline behaviors of the crystalline phase at elevated temperatures and the pristine amorphous phase at room temperature. Here, we investigate the structural evolution of CGST using combined in situ techniques. Our in situ x-ray diffraction and ellipsometry results demonstrate that CGST exhibits a much higher phase transition temperature than undoped one. Temperature-dependent in situ transmission electron microscopy observations further reveal that carbon doping plays a critical role in tailoring the properties of GST by tuning the stochasticity of nucleation/crystallization, stabilizing amorphous and crystalline GST via isolating and refining the grain size at room temperature and elevated temperature. Our work provides detailed information for understanding the microscopic origin of crystallization kinetics of carbon-doped phase change materials toward high-performance PCRAM.

Electrochemical properties of Li-rich ternary cathode material Li1.20Mn0.44Ni0.32Co0.04O2 and its oxygen-deficient phase

As the cathode material of lithium-ion batteries, Li-rich ternary layered oxides usually suffer from high first cycle irreversible capacity, low rate capability, and structural instability during charge–discharge. Recent studies show that Ni-rich Li1.20Mn0.44Ni0.32Co0.04O2 material has good structural stability. In this paper, the electrochemical performance of Li1.20Mn0.44Ni0.32Co0.04O2 and its oxygen-deficient phase Li1.20Mn0.44Ni0.32Co0.04O1.83 are studied by the first-principles calculations. The results show that, for the pristine phase Li1.20Mn0.44Ni0.32Co0.04O2, the theoretical delithiation capacity is 380 mAh/g and the highest charging voltage platform is 4.99 V. The O ions are found to participate in the charge compensation significantly. Ni ions can only contribute 118 mAh/g of the delithiation capacity, and the remaining charging capacity is contributed by O ions. For the oxygen-deficient phase Li1.20Mn0.44Ni0.32Co0.04O1.83, the highest voltage platform is reduced by 0.21 V, O ions are also found to participate in the charge compensation obviously. Compared to the pristine phase, transition metal (TM) ions in the oxygen-deficient phase exhibit higher chemical activity, while the contribution of O ions to charge compensation is relatively reduced. The oxygen-deficient phase has a slightly higher theoretical capacity (392 mAh/g) than the pristine phase.

Performance analysis of P-SnS thin films fabricated using CBD technique for photo detector applications

In the present work, SnS thin films were prepared using the CBD technique at room temperature and varying annealing temperaturesfrom300 to 450 °C for photo detector applications. The prepared samples were characterized using different techniques for analyzing the structural, optical, morphological, and photo sensing properties of the samples. From XRD analysis, the diffraction pattern of all the prepared thin films shows the pristine SnS phase of the samples possessing an orthorhombic phase without the presence of any impurity phases. Among the fabricated thin films, the SnS thin film annealed at a temperature of 350 °C reveals the highest crystallite size. The Raman results showed the vibrational modes of SnS films and with the increase in growth temperature, the peaks are slightly shifted towards the lower wavelength region. Morphological results show that the SnS thin films exhibit a uniform morphology of 2-D petal-like morphology with different sizes. The UV-vis spectroscopic study shows the decrease in the bandgap value of the samples with the increase in annealing temperature. The photo sensing properties of the fabricated samples show the SnS sample annealed at 400 °C has a higherresponsivityvalueof6.40×10⁻²AW⁻¹,externalquantumefficiency(EQE)valueof14.9%, and the detectivity value of 6.05 × 10⁹ Jones. Finally, the transient photo response results suggest that the SnS annealed at 350 °C shows a rise and fall time of 1.5 and 2.5 s compared to the othersampleswhichwouldbebettersuitedforphotodetectorapplications. The electrical conductivity and photo-conductivity of the films increase by more than two orders with increase of film thickness from 170 nm to 915 nm. Hall Effect measurements confirm the p-type nature of the as-prepared SnS thin films.