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Trivalent samarium activated β-Wollastonite (β-CaSiO3:Sm3+) nanostructured phosphor powders have been synthesized by modified sol-gel method at various concentrations (0.0, 0.2, 0.4, 0.6, 0.8 and 1 mol %) employing rice husk ash (RHA) and eggshell (ES) as the precursors for SiO2 and CaO respectively. The powder x-ray diffraction peaks disclose structure of sintered samples as monoclinic structure with space group P1 21/c1. The average crystallite sizes were determined by Debye scherrer's formula in the range of 26–34 nm. The average particle size was 84.5 nm found from TEM images. The photoluminescence excitation (PLE) spectra recorded high intensity peak at 400 nm was owing to 6H5/2 → 4K11/2 transition. The emission (PL) spectra of prepared samples exhibit intense orange–red color emission peak at 602 nm due to 4G5/2 → 6H7/2 transition. All the prepared samples emission tuned towards white region of the CIE diagram with the increment of Sm3+ content. This new nanostructured phosphor material could be a probable candidate for white light display and solid-state lighting (SSL) applications.

In the present study, CaZrO3 nanophosphors were sensitized with lanthanum (La) at different concentrations (0.5, 1.0, 1.5, 2.0, and 2.5) prepared using polyvinyl alcohol as the chelating agent through the sol-gel method. To study their structural and optical properties, samples were characterized by X-ray diffractometry (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and photoluminescence (PL). The XRD results revealed that samples were well crystallized and average crystallite sizes were calculated. The average crystallite size value was in good agreement with the value obtained from TEM analysis. Energy dispersive spectroscopy and FE-SEM confirmed the existence of La in the prepared samples. In the PL spectra, La-sensitized samples exhibited three bands at 402 nm, 438 nm, and 463 nm in the visible range when excited at the 260 nm wavelength. As the proportion of La increased, the intensity of bands at 438 nm and 463 nm decreased, whereas the band at 402 nm remained stable. Time-resolved PL spectra illustrated the lifetime of the samples. Corresponding CIE co-ordinates for La-sensitized CaZrO3 were calculated.

Fast sodium ion conducting Na11Sn2PSe12 solid electrolyte was prepared by a mechanochemical method. This is the first tin based selenide prepared by room temperature ball milling instead of conventional synthesis in a sealed quartz tube under vacuum. Our approach is safe and easy to scale up. Samples were synthesized systematically using various intervals of ball milling and annealing time to maximise phase purity and ionic conductivity. The highest room temperature bulk ionic conductivity of the mechanochemically synthesized Na11Sn2PSe12 was 1.0 mS cm−1 observed for a sample prepared by ball milling for 15 h followed by 6 h annealing at 550 °C. This fast-ion conducting Na11Sn2PSe12 allowed to demonstrate the first Na–Se all-solid-state batteries Na/Na11Sn2PSe12/C–Se and Na3Sn/Na11Sn2PSe12/C–Se with specific initial discharge capacities of 430 mA h g−1 or 400 mA h g−1, respectively at a current density 0.08 mA cm−2. The Na3Sn/Na11Sn2PSe12/C–Se battery could be cycled 500 times with a capacity that decreased gradually to 50 mA h g−1.

The incorporation of germanium into Cu2ZnSn(S,Se)4 thin films is gaining a massive attention because of its potential to tailor the properties of kesterite absorbers resulting in high efficiency solar photovoltaic devices. The present work reports the growth of Cu2Zn(Sn,Ge)Se4 (CZTGSe) thin films by incorporation of germanium during the deposition of precursor film consisting of multiple stacks of (Sn/Se/Ge/Se/ZnSe/Se/Cu/Se). The precursor stacks were sequentially evaporated onto soda lime glass substrates held at 100 °C in high vacuum. Subsequent selenization of precursor films in a horizontal tubular furnace at 425 °C led to the formation of single phase Cu2Zn(Sn0.7Ge0.3)Se4 films. X-ray diffraction pattern of stacked layers selenized at 425 °C revealed the formation of Cu2Zn(Sn,Ge)Se4 films with a preferred orientation along (112) plane. Rietveld refinement corroborated the growth of kesterite-type CZTGSe having tetragonal structure with lattice constants of a = 5.678 A and c = 11.304 A. Raman measurements performed using multiple excitation wavelengths confirmed the growth of single phase Cu2Zn(Sn,Ge)Se4 films. Secondary ion mass spectroscopy (SIMS) depth profiles of stacked layers selenized at 425 °C illustrated a uniform distribution of constituent elements in Cu2Zn(Sn0.7Ge0.3)Se4 films. The FESEM images showed relatively uniform and spherical grains of 100–150 nm in size. Optical absorption studies of the films showed an optical band gap of 1.19 eV with high absorption coefficient (> 104 cm−1). The films exhibited p-type conductivity with a resistivity of 69.8 Ω cm, mobility of 38.35 cm2(Vs)−1 and carrier concentration of 2.33 × 1015 cm−3.

Solvothermal synthetic routes can provide energy-savvy platforms to fabricate battery anode materials involving relatively milder annealing steps vis-a-vis the conventional solid-state synthesis. These energy efficient routes in turn restrict aggressive grain growth to form nanoscale particles favouring efficient Li+ diffusion. Here, we report an economic solution combustion synthesis of SrLi2Ti6O14 anode involving nitrate-urea complexation with a short annealing duration of only 2 h (900 °C). Rietveld refinement confirms the phase purity of target product assuming an orthorhombic framework (Cmca symmetry). It delivers reversible capacity of ∼125 mAh.g−1 at a rate of C/20 involving a 1.38 V Ti4+/Ti3+ redox activity with excellent rate kinetics and cycling stability. Bond valence site energy (BVSE) calculations gauge SrLi2Ti6O14 to be an anisotropic 3D Li+ ion conductor with the highest ionic conductivity along the c direction. The electrochemical and diffusional pathways have been elucidated for combustion prepared SrLi2Ti6O14 as an efficient and safe negative electrode candidate for Li-ion batteries.

Six possible multiple stacks of Cu-ZnSe-Ge with selenium incorporation at a precursor stage were prepared using electron beam evaporation followed by vacuum selenization at 475 °C for 30 min to investigate the role of stacking order on the growth and properties of Cu2ZnGeSe4 films. The X-ray diffraction measurements affirm the existence of various binary and ternary phases (ZnSe, Cu2Se, GeSe2 and Cu2GeSe3) for all the precursor stacks. These phases are completely diminished after selenization at 475 °C except a minor co-existence of ZnSe (111) phase along with dominant Cu2ZnGeSe4 (112) phase for stack A: (Cu/Se/ZnSe/Se/Ge/Se) × 4. The Raman measurements for selenized multiple stack A, revealed two major A3, A1 modes at 206 cm−1 and 176 cm−1 and one minor E5 mode at 270 cm−1 corresponding to CZGSe phase. The surface morphology and the elemental distribution across the thickness found to vary significantly with the change of stacking order. The selenized multiple stacks A films shows densely packed flake and capsule shaped grains. The selenized stack A found to have a direct energy band gap of 1.60 eV, showing p-type conductivity with a Hall mobility of 22 cm2 (Vs)−1.

In this work a facile two-step process, comprising of e-beam evaporated precursor deposition of (In/Cu/Ag/Se)× 3 multi-stack over substrate followed by additional selenization treatment, has been used to grow high-quality Cu0.5Ag0.5InSe2 (CAISe) films. The post selenization was performed at distinct temperatures in the range, 300 °C - 500 °C, and the effect of selenization temperature on the growth of CAISe thin films was reported in detail. The post selenization of (In/Cu/Ag/Se)×3 precursors at temperatures

In this study, we demonstrate the pre-annealing treatment of stacked precursors at 250 °C for different durations (5, 10, 15, 20, 30, and 60 min), subsequently selenized at 400 °C for 1 min and correlate its effects on structural, morphological, and optoelectronic properties of Ag2ZnSnSe4 films (AZTSe) with a detailed characterization. After investigating pre-annealing treatment duration, the grown AZTSe films show various binary/ternary phases and appreciable transformation in surface morphology. However, stacked layers pre-annealed for 20 min and selenized at 400 °C for 1 min show a single-phase kesterite AZTSe with two main Raman peaks at 181 and 198 cm−1 with compact and larger grains (~0.53 μm). The bond length and bond angles for single-phase AZTSe films are evaluated using Rietveld refinement of X-ray diffraction data. The core-level X-ray photoelectron spectra confirm the oxidation formula as Ag2+1Zn+2Sn+4Se4−2 and uniform distribution of elements is established by secondary ion mass spectrometer measurements, for precursor films pre-annealed at 250 °C for 20 min and selenized at 400 °C for 1 min. They possess n-type conductivity with a maximum mobility of 79.4 cm2(Vs)−1 and a direct band gap of 1.37 eV.

The Cu2ZnSnSe4(CZTSe) thin films were prepared by a two-step process consisting of high vacuum sequential evaporation of precursors stack (Sn/Se/ZnSe/Se/Cu/Se) in 4-folds followed by selenization at 350 °C in tubular furnace under varied argon gas pressure from 1 mbar to 600 mbar with an interval of 150 mbar. The Cu/(Zn + Sn) and Zn/Sn ratios found to vary from 1.22 to 0.93 and 1.94 to 1.08 with an increase in pressure and the stacks selenized for 600 mbar showed nearly stoichiometric composition with slight Cu-poor and Zn-rich values required for CZTSe growth. The X-ray diffraction studies revealed similar diffraction pattern with a preferred orientation along (112) plane, indicating the formation of kesterite-type CZTSe for all the selenization pressures. Raman spectra recorded using different excitation wavelength sources (785, 532 and 458 nm), revealed two main peaks at 192 and 172 cm−1 and two supplementary weak peaks at 82 and 232 cm−1 corresponding to kesterite-ordered CZTSe phase for films selenized at a pressure of 600 mbar. Appreciable changes in morphology have been noticed with increase in selenization pressure from low dense irregular rod like morphology to compact spherical grain morphology. All the samples showed high absorption coefficient (>104cm−1). A slight variation in optical band gap from 0.90 to 1.01 eV was found with increase in selenization pressure. The Hall effect measurements reveal that all the films are p-type conductive. The precursor stack films selenized at 600 mbar exhibit high mobility of 7.88 cm2(Vs)−1 with lower carrier concentration of 2.54 × 1019 cm−3 and resistivity of an order of 10−2 Ωcm, respectively.

In the present paper, a novel process for synthesis of Cu2ZnSnSe4 thin films via low temperature selenization (350 A degrees C) of multiple stacks of binary selenides has been reported. Further, the influence of selenization temperature (250-450 A degrees C) on the physical properties of Cu2ZnSnSe4 thin films was studied and discussed herein. The Rietveld refinement from X-ray diffraction data of Cu2ZnSnSe4 films grown at a selenization temperature of 350 A degrees C was found to be single phase with kesterite type crystal structure and having lattice parameters a = 5.695 , c = 11.334 . Raman spectra recorded using multi excitation wavelength sources under non-resonant and near resonant conditions confirms the formation of single phase Cu2ZnSnSe4 films. Secondary ion mass spectroscopic (SIMS) analysis demonstrated that composition of elements across the thickness is fairly uniform. Energy dispersive X-ray analysis measurement reveals that the obtained films are Cu-poor and Zn-rich. The scanning electron micrographs of binary selenide stacks selenized at a temperature of 350 A degrees C shows randomly oriented cylindrical grains. The optical absorption studies indicated a direct band gap of 1.01 eV. The films showed p-type conductivity with electrical resistivity of 4.66 a''broken vertical bar cm, Hall mobility of 15.17 cm(2) (Vs)(-1) and carrier concentration of 8.82 x 10(16) cm(-3).

Ce activated CaZrO 3 nanophosphors were prepared at different concentrations (0.2, 0.4, 0.6, 0.8 and 1.0 wt %) through sol–gel method utilizing polyvinyl alcohol as a chelating agent. The as-obtained samples were investigated using the characterization techniques such as X-ray diffraction (XRD), field emission scanning electron microscope (FESEM-EDAX), transmission electron microscope (TEM), photoluminescence (PL), Raman, Fourier transform infrared (FTIR) and UV–Visible absorption spectroscopy respectively. The crystallite sizes were calculated by XRD patterns. Agglomeration nature of the samples were observed from FESEM images of samples. The energy dispersive spectroscopy (EDS) measurements affirm the existence of Ca, Zr, O and Ce elements in the samples. From TEM images, the average particle sizes of the samples were calculated and compared with obtained XRD values. The samples' energy gap was derived from UV–Vis spectra. When the samples were excited with 250 nm, three emission peaks at 400 nm, 423 nm and 466 nm were obtained. From CIE diagram, the corresponding CIE co-ordinates were calculated and found to be located in blue region.

Rechargeable batteries play a pivotal role in conversion of chemical energy to electrical energy and energy storage. Lithium batteries have been considered as promising power supply for various electric vehicles and grid storage systems. However, the formation of lithium dendrites and use of liquid electrolytes turned out to be the major impediment in realising the potential of these batteries. To overcome these challenges here we demonstrate the use of various fast-ion conducting solids as solid electrolytes in semi-flow Li–S batteries containing catholyte slurries. Lithium conducting Li 7 P 3 S 11 was prepared using ball- milling followed by annealing at 250 °C. Rietveld refinements of compounds indicated that the product is Li 7 P 3 S 11 with space group P- 1 and lattice parameters of a = 12.42(2) A, b = 6.066(9) A, c = 12.52(8) A. The Li 7 P 3 S 11 produced exhibits an ionic conductivity of the order of 7.1 × 10 − 4 S/cm at 30 °C. Here, we investigate the stability of these solid electrolytes in contact with catholytes consisting of polysulfide, Li 2 S 8 , dissolved in monoglyme. Li 2 S 8 /Li 7 P 3 S 11 /Li semi-flow rechargeable battery exhibited an initial discharge specific capacity of 1268 mAh/g at 1 C rate and retained 748 mAh/g after the 10th cycle.

The aim of achieving high-energy, long-life, safe and low cast storage batteries has brought tremendous scientific attention in the last decade, resulting in significant improvements in the stored energy of cathodes and anodes particularly in lithium-based battery technology. However, presently available lithium-ion technology cannot satisfy the increasing demand for energy density. Li–S battery is a typical example, which can offer theoretically a fivefold increase in energy density compared with conventional lithium rechargeable batteries. Despite significant advances, there are challenges to its wide-scale implementation, which include dissolution of intermediate polysulphide reaction species into the electrolyte when liquid polysulphide is used as cathodes. Another problem is preparation of polysulphides. Here we report a novel approach to replace the liquid electrolyte with solid lithium conducting membranes, Argyrodite (Li6PS5X(X = Cl,Br)) and Li10GeP2S12 solid electrolytes to mitigate the problem. Among the three solid electrolyte membranes Li10GeP2S12 exhibited high first discharge specific capacity of 1435 (±3) mAh g−1 at 0.5 C rate.

Due to their high ionic conductivity and stability versus metallic lithium, garnet-related Li 7 La 3 Zr 2 O 12 (LLZ) are of interest as Li + solid electrolytes. The correlation between structure and ion mobility in undoped, Ta 5 + , Nb 5 + , Ga 3 + or Al 3 + doped LLZ is studied combining molecular dynamics (MD) simulations and experimental characterisation. Neutron and in situ XRD powder diffraction are employed to analyse the Li and dopant distribution and temperature dependence of the structure. Pentavalent doping enhances ionic conductivity by increasing the vacancy concentration and reducing local Li ordering. Trivalent doping Al 3 + or Ga 3 + on the Li site is slightly less effective in enhancing conductivity. Ga 3 + doping on the La 3 + site only helps to retain the cubic phase, but does not affect the mobile charge carrier concentration. The cooling rate after sintering is found to strongly affect both the ionic conductivity and its hysteresis on subsequent thermal cycling in the low temperature range, which can be attributed to local Li ordering as manifested by non-linear variations of the lattice parameters.

LiFePO4 was prepared using carbothermal reduction method. In-situ temperature dependent structural studies were carried using X-ray diffraction. Molecular dynamics simulations were conducted for the LiFePO4 using empirical potentials developed using bond valence approach to investigate the structural variations. Electrochemical behaviour of LiFePO4 was evaluated using cyclic voltammetry and galvanostatic cycling studies at room temperature. Charge–discharge cycling studies showed a reversible capacities 140 (±5) mAh g−1 at the end of 50th cycle and these capacity values were stable up to 400 cycles and almost nil capacity fade between 50 and 400 cycles, showing excellent capacity retention, low capacity fading. The cyclic voltammetry studies showed a main cathodic and anodic redox peaks at 3.34 and 3.5 V vs. Li, respectively.

The favorable combination of fast-ionic conductivity and high electrochemical stability of Li-stuffed garnet type Li7La3Zr2O12 (LLZ) makes this material a promising candidate for applications as a solid-state electrolyte in high-energy-density batteries. However, a widespread technical use of LLZ is impeded by difficulty in reliable formation and densification of the pure fast-ion conducting phase. The present study of the phase-formation process enables rational fabrication procedures to be devised based on a thorough understanding of the complex phase formation of LLZ. In situ neutron powder diffraction monitoring of the phase formation revealed an influence of the partial melting of precursors on the formation of the fast-ion conducting phase, indicating that in the typical synthesis route LLZ is not formed in a solid-state reaction but from a partial carbonate melt that decomposes on further heating. The cooling rate critically influences lithium ordering and ionic conductivity.

The molten-salt method was used to synthesize a series of transition-metal containing titanium dioxides. Some of the transition metals were found to substitute into the TiO2 lattice, such as (Ti0.9Fe0.1)O2, (Ti0.9Zr0.1)O2, (Ti0.9V0.1)O2, and (Ti0.9Mn0.1)O2, while others were formed as composite electrodes (in addition to relatively minor substitutions), namely 0.1SnO2–0.9TiO2 and 0.05NiO–0.1Nb2O5–0.9TiO2. Although identical synthesis-conditions were used the different transition metals yielded different phases. A comparative study of the electrodes relating surface area and composition (via X-ray photoelectron spectroscopy, XPS), and electrochemical behaviour is presented in this work. Among the substituted single phase electrodes, (Ti0.9Zr0.1)O2 exhibited the best reversible capacity of ∼160 mA h g−1, at the end of the 60th cycle in the voltage range 1.0–2.6 V, with a capacity fade of 24% from the 2nd to the 60th cycle. Among the composite electrodes, 0.05NiO–0.1Nb2O5–0.9TiO2 shows the best performance which is comparable to pure TiO2 but with a slower capacity-fade on extended cycling. The worst performing electrode is (Ti0.9V0.1)O2 with a reversible capacity of only ∼70 mA h g−1 at the end of 70 cycles with a current density of 130 mA g−1 in the voltage range 1.0–2.6 V and a capacity drop of 52% from the 2nd to the 70th cycle. The composite 0.1SnO2–0.9TiO2 features the highest irreversible capacity-loss. Zr-substitution into TiO2 gives the best electrochemical performance.

Lithium-ion conducting argyrodites Li6PS5X (X = Cl, Br, I) are a promising class of fast-ion conductors for all-solid state Li-ion batteries. To gain a deeper insight into the phase formation of Li6PS5Cl, in situ neutron diffraction studies are carried out on a stoichiometric ball-milled precursor mixture during thermal treatment. The evolution of the S2 −/Cl− anion disorder and its correlation with ionic conductivity are reported here. In contrast to earlier reports, an argyrodite phase is found to form between 80 and 150 °C, but the phase shows only moderate conductivity when crystallized at such low temperatures and further thermal treatment is required to access the highly conducting phase. The maximum room-temperature ionic conductivity of 1.1 × 10− 3 S/cm is observed for samples annealed at intermediate temperatures (250 °C). When ball-milled glass-ceramic precursors for Li6PS5Cl are crystallized with a constant slow heating rate, the initially formed argyrodite phase is found to be Li7PS6, which is then gradually converted into Li6PS5Cl at higher temperatures. The industrial requirements for minimizing cost by using lower annealing temperatures thus need to be balanced with the requirements of obtaining the highest conducting composition of the phase for performance in all-solid state batteries.

Multiple stacks of precursors (Cu/Se/ZnSe/Se/Ge/Se) are deposited by electron beam evaporation followed by selenization in high vacuum at substrate temperatures ranging from 350 degrees C - 500 degrees C for 30 min to achieve device quality Cu2ZnGeSe4 films. The effect of selenization temperature on the structural, morphological, compositional, optical and electrical properties of Cu2ZnGeSe4 films are studied and discussed systematically. The crystal structure of Cu2ZnGeSe4 thin films selenized at 450 degrees C is found to be tetragonal stannite with lattice parameters a = 5.592(1) angstrom and c = 11.057(5) angstrom. The energy dispersive spectroscopic studies revealed the presence of Cu-poor and Zn-rich Cu2ZnGeSe4 films. The secondary ion mass spectroscopic (SIMS) analysis has been carried out to know the distribution of constituent elements across the thickness and found to be fairly uniform. The micrographs of Cu2ZnGeSe4 films selenized at 450 degrees C showing perfectly packed rice shaped cylindrical grains. Raman spectra revealed the existence of a minor ZnSe binary phase along with Cu2ZnGeSe4 phase. The optical energy band gap of Cu2ZnGeSe4 films was found to be 1.6 eV and these films have p-type conductivity with electrical resistivity of 2.13 x 10(-3) Omega cm. (C) 2016 Elsevier Ltd. All rights reserved.

High ionic conductivity is one of the key characteristics of electrolytes and electrode materials directly affecting performance of electrochemical devices in which they are used. In the case of inorganic crystalline solid electrolytes and insertion cathodes the topology and geometry of crystal structure essentially defines ionic conductivity and charge–discharge rates. We employed the bond valence method to identify materials with crystal structures featuring infinite networks of pathways of suitable size that is a prerequisite for fast ion transport. Taking advantage of the method low computational cost, we carried out exhaustive analysis of ~ 13,000 entries of the Inorganic Crystal Structure Database and ranked the materials based on the fraction of crystal structure space with low bond-valence mismatch. The results may be used as a guide for further theoretical and experimental studies of promising compositions.

Pure and doped Li 6− x (Zr 2− x M x )O 7 , M = Nb and Ta; x = 0, 0.15 compounds have been prepared by the urea combustion method followed by annealing at 950 °C for 8 h. The samples are characterized by X-ray diffraction and impedance spectroscopy. Ionic conductivities, σ ionic , were determined in the temperature range of 60–360 °C by impedance spectroscopy. We observe that the Ta doped Li 6 Zr 2 O 7 has a measurable σ ionic at ∼160 °C, and at 300 °C exhibits a conductivity value of 1 × 10 −3 S/cm. The temperature dependence of the conductivity in the range 100–360 °C obeys an Arrhenius relation, yielding an activation energy of E a = 0.95 eV (for M = Ta and x = 0.15). The bond valence approach has been used to visualise Li + ion migration pathways and the conductivity mechanism in these compounds. The lowest energy pathway is found to extend along the [0 1 2] direction. The Bond valence analysis also indicates a significantly anisotropic Li-ion conductivity in compounds with Li 6 Zr 2 O 7 type structure, predicting activation energies of 1.1 and 0.9 eV for the low energy pathway in undoped and doped Li 6 Zr 2 O 7 .

The effects of substrate temperature and selenization temperature on the structure, composition, electrical and optical properties of Cu2SnSe3 films were studied systematically. Cu2SnSe3 films deposited at various substrate temperatures (303–573 K) by the flash evaporation method are found to be non-stoichiometric. To compensate the selenium deficiency and obtain a single-phase, an annealing Cu2SnSe3 films deposited at 573 K was performed in selenium atmosphere. Cu2SnSe3 films deposited at a substrate temperature of 573 K and then selenized at 673 K were single phase and polycrystalline exhibiting monoclinic structure. The films showed p-type conductivity with a direct band gap of 0.84 eV.

Empirical bond length–bond valence (BV) relations provide insight into the link between structure of and ion transport in solid electrolytes and mixed conductors. Building on our earlier systematic adjustment of BV parameters to the bond softness, here we discuss how the squared BV mismatch is linked to the absolute energy scale and used as a general Morse-type interaction potential for analyzing low-energy ion migration paths in ion conducting solids or mixed conductors by either an energy landscape approach or molecular dynamics (MD) simulations. For a wide range of lithium oxides we could thus model ion transport revealing significant differences to an earlier geometric approach. This novel BV-based force-field has then been applied to investigate a range of mixed conductors, focusing on cathode materials for lithium ion battery (LIB) applications to promote a systematic design of LIB cathodes that combine high energy density with high power density. To demonstrate the versatility of the new BV-based force field it is applied in exploring various strategies to enhance the power performance of safe low cost LIB materials including LiFePO4, LiVPO4F, LiFeSO4F, etc.

The intrinsic formation of polyatomic defects in Sc 2 (WO 4 ) 3 -type structures is studied by Mott Littleton calculations and Molecular Dynamics simulations. Defects involving the WO 4 2− tetrahedron are found to be energetically favorable when compared to isolated W and O defects. WO 4 2− Frenkel and (2Sc 3+ , 3WO 4 2− ) Schottky defects exhibit formation energies of 1.23 eV and 1.97 eV, respectively and therefore may occur as intrinsic defects in Sc 2 (WO 4 ) 3 at elevated temperatures. WO 4 2− vacancy and interstitial migration processes have been simulated by classical Molecular Dynamics simulations. The interstitial defect exhibits a nearly 10 times higher mobility (with a migration energy of 0.68 eV), than the vacancy mechanism (with a slightly higher migration energy of 0.74 eV) and thus should dominate the overall ionic conduction. Still both models reproduce the experimental activation energy (0.67 eV) nearly within experimental uncertainty.

The x M 2 O–(1 − x )SiO 2 (M = Li, Na, and K, and 0.1 ≤ x ≤ 0.5) glass systems have been studied by constant volume molecular dynamics (MD) simulations. The bond valence (BV) method is applied to the equilibrated configurations to analyse the structural variation in these glass systems with increasing network modifier content, its consequence for M + ion mobility, as well as the distribution of bridging and non-bridging oxygen atoms and the variation of the Q i values. The contribution of non-bridging oxygen atoms to the BV sums exhibits a transition around x = 1/3 for Li 2 O and Na 2 O doped glasses. The observed Q i variation is consistent with a bond order model. Despite slight deviations of the interatomic distances in the MD-simulated glasses, their BV analysis reveals characteristic features of the ion transport pathway. For complex disordered systems with low ion mobilities the bond valence analysis of the pathway characteristics for the mobile ion is thus a viable method to extract ion transport properties even if the mobilities are too low to be directly analysed from the mean square displacements over the simulated period.

Correlations between the ionic conductivity and antisite disorder in low cost cathode materials (1D Li+ conducting LiFePO4 and quasi-1D LiFeSO4F) and the origin of the experimentally observed drastic conductivity enhancement in nanoscale heterostructures LixFePO4:Li4P2O7 are explored by molecular dynamics (MD) simulations with a novel bond valence (BV) based force-field. Compared to bulk values, ionic conductivity in surface-modified LixFePO4 is enhanced by up to 3 orders of magnitude. Details of dynamic ion transport pathways are extracted by our BV transport pathway analysis applied to MD simulation trajectories. Besides heterogeneous doping by the redistribution of mobile ions across the interface, ion mobility varies as quantified via the extension of unoccupied accessible pathway regions. A layer-by-layer analysis indicates a maximum mobility close to the interface, but Li+ mobility remains enhanced even at the center of the simulated nanocrystals. Li+ diffusion in LiFeSO4F exhibits a pronounced anisotropy with a “superionic” zig–zag pathway parallel to [111] involving partially occupied Li sites. A notable long range ion diffusion rate can be maintained in macroscopic LiFeSO4F crystals due to the moderate activation energy for migration perpendicular to the channels.

Molecular dynamics (MD) simulations with a dedicated force-field in combination with our bond valence (BV) pathway analysis have been employed to reproduce and explain the experimentally observed ultrafast Li+ transport in surface modified LixFePO4-δ as a consequence of heterogeneous doping, i.e. the Li+ redistribution in the vicinity of the interface between LixFePO4 and a pyrophosphate glass surface layer. Over the usual working temperature range of LIBs Li+ ion conductivity in the surface modified LixFePO4 phase is enhanced by 2-3 orders of magnitude, while the enhancement practically vanishes for T > 700K. Simulations for the bulk phase reproduce the experimental conductivities and the activation energy of 0.57eV (for x ≈ 1). A layer-by-layer analysis of structurally relaxed multilayer systems indicates a continuous variation of Li+ mobility with the distance from the interface and the maximum mobility close to the interface, but Li+ diffusion rate remains enhanced (compared to bulk values) even at the center of the simulated cathode material crystallites. Our BV migration pathway analysis in the dynamic local structure models shows that the ion mobility is related to the extension of unoccupied accessible pathway regions. The change in the extent of Li redistribution across the interface with the overall Li content constitutes a fast pseudo-capacitive (dis)charging contribution.

Li1.4N1.6M0.4(PO4)3 with M = Al, Ga, N = Ti, Ge were prepared by annealing of the mixtures at 800°C. X-ray diffraction showed the formation of NASICON phase with space group R-3c along with a minor impurity second phase. Rietveld refinement of the X-ray data was performed to identify the structural variation. The compound with N = Ti and M = Al exhibited lattice parameters a = 8.5015 Aå and c = 20.820 Aå, slightly lower than for the undoped Ti compound (N = M = Ti). Measurements of σionic were carried out on sintered pellets by impedance spectroscopy at 30°C, highest ionic conductivity 2.57 x 10-4 S/cm among the prepared samples was observed when N = Al and M = Ti, two orders of magnitude higher than for the undoped case. Bond valence approach was applied to visualize the migration pathways of Li+ ion and barrier energies were estimated. Obtained Li site energy landscapes indicate the continuous Li transport pathway accessible with activation energy of 0.45eV for undoped Li1Ti2(PO4)3 and 0.42 eV for N = Al and M = Ti doped compound.

The x Li 2 O–(1 − x )SiO 2 ( x = 0.1, 0.15, 0.2, 0.25, 0.3, 0.33, 0.4, 0.45, and 0.5) glass systems have been studied by constant volume molecular dynamics (MD) simulations, using empirical pairwise Morse-type potentials. Bond valence (BV) method is applied to the equilibrated configurations to analyse the structural variation in these glass systems with increasing network modifier content, its consequence for Li + ion mobility, as well as the distribution of bridging and non-bridging oxygen atoms and the variation of the Q i values. The contribution of non-bridging oxygen atoms to the Lithium BV sums exhibits a transition around x = 1/3. The observed Q i variation can be explained by a bond order model. Despite slight deviations of the interatomic distances in the MD-simulated glasses, their BV analysis reveals features of the ion transport pathway (such as volume fraction and local dimensionality of the percolating pathway). Results are compared to pathway models for related glassy solid electrolytes based on reverse Monte Carlo modelling of diffraction data. For complex disordered systems with low ion mobilities the bond valence analysis of the pathway characteristics for the mobile ion is thus a viable method to extract ion transport properties even if the mobilities are too low to be directly analysed from the mean square displacements over the simulated period.

xLiCl–(1 − x)(0.6Li2O–0.4P2O5) systems with x = 0.1, 0.15, 0.2, 0.25, have been prepared using melt quenching method and their ionic conductivity was characterized by impedance spectroscopy. Molecular dynamics (MD) simulations for the same systems have been performed with an optimized potential, fitted to match bond lengths, coordination numbers and ionic conductivity. Based on the equilibrated configurations of these MD simulations, ion transport pathways are modelled in detail by the bond valence approach to clarify the influence of the halide dopant concentration on the glass structure and its consequence for Li ion mobility. Features of the consequential ion transport pathway models (such as volume fraction and local dimensionality of the percolating pathway) are compared to pathway models for related glassy solid electrolytes based on reverse Monte Carlo modelling of diffraction data.

The unique diffusion mechanism in the novel polyatomic anion conductor scandium tungstate is studied by molecular dynamics simulations of systems with artificially induced WO4 2− defects and compared to our previous simulations of defect-free structure models. The diffusion activation energy obtained from structures with built-in defects is smaller than for the defect-free models and in the case of tungstate vacancies close to the experimental value, suggesting that extrinsic tungstate vacancies due to the volatility of WO3 are important for the experimental conductivity. The validity of the force field used for the molecular dynamics simulations is further verified by investigating the orthorhombic to monoclinic phase transition of Sc2(WO4)3 under compression. The lattice compressibility in both phases and the phase transition is qualitatively reproduced, though the simulated phase transition pressure occurred is about 0.55 GPa higher than the experimental one.

Discussions about the nature of the charge carriers in the scandium tungstate and other isostructural tungstates and molybdates have persisted in the literature since a variety of experimental indi...

Amorphous solid electrolytes in the system xLi2O-(1 - x)(0.6Li2S-0.4P2S5) (with x = 0.1, 0.15, 0.2, 0.25, 0.3, 0.35 and 0.4) have been prepared from a mixture of Li2O, Li2S and P2S5 using a mechanical milling technique at room temperature and in inert atmosphere. The oxysulfide powder mechanically milled for 80 h with x = 0.25 shows an ionic conductivity (?) of 2.5 � 10-4 S cm-1 at 300 K which is the highest in this series. The glass transition temperature (Tg) exhibits a minimum at x = 0.25. Constant volume molecular dynamics was done for all x. Structural and transport results from molecular dynamics (MD) simulation are described. Changes in structure with x and their influence on ? and Tg are discussed. � 2006 Elsevier B.V. All rights reserved.

The analysis and prediction of ion transport in solids from static and dynamic structure models has become an interesting application for the bond valence approach. Specific adaptations of the bond valence approach for this application area are discussed, and the resulting predictions are compared to those from alternative screening approaches. A particular advantage is that the bond-valence-based approach can be applied to both crystalline and glassy solids and that the level of computational effort can be easily adjusted to the level of detail required in the prediction from static pathway models for screening purposes to bond-valence-based molecular dynamics simulations for analyzing the coupling between the migration of the mobile species and rearrangements in the immobile substructure.

ZSM-5 was prepared without the aid of an organic template. Effect of synthesis parameters on its catalytic activity in aromatisation ofn-heptane are discussed. Addition of seed material increased the crystallinity of the ZSM-5 phase. The catalytic activity was comparable with a sample prepared using an organic template. Formation of higher amount of C9– aromatics was observed over the non-templated zeolite.