Decrease In Lattice Volume Research Articles

Role of site–specific doping in stabilizing high–nickel cathodes for high-performance lithium- ion -batteries

The growing demand for high-capacity and energy-dense lithium-ion batteries has driven the increase of nickel content in commercially available cathodes. However, during deep charging (delithiation), these Ni-rich cathodes experience a detrimental phase transformation and a sudden, significant decrease in lattice volume. This lattice collapse is considered the primary culprit behind the limitations in the cathode's electrochemical performance. Notably, the exact cause-and-effect relationship between the phase change and the collapse remains unclear. In the present study, the effect of the site of substitution on the performance of the LiNiO2 cathode has been investigated by adopting tungsten as a dopant. To gain deeper insights into this connection within Ni-rich LiNiO2, the contraction of the c-axis and the change in the a-axis during the delithiation have been investigated using ab initio density functional theory. Findings reveal that the free energy difference between the suspected phases in Ni-rich LiNiO2 is minimal at room temperature, facilitating the transition from the H2 to the H3 phase. This transition appears to be driven by the movement (gliding) of the NiO2 layer towards the adjacent Li layer. The findings of the present study indicate that among two different configurations due to different sites of substitution, the WLNO-2 configuration suppresses H2 –H3 phase conversion to a greater extent by hindering the gliding of the NiO2 layer toward the Li layer. Furthermore, a reduction in the collapse of the c-axis lattice during deep de-lithiation for the WLNO-2 configuration has been observed. This reduced collapse is primarily attributed to the altered charge distribution within oxygen atoms and the weakened screening effect from lithium ions.

Chemical stability and leaching mechanism of YIG and HEG at different pH conditions

AbstractDesigning waste forms using the cocktail effect of high‐entropy ceramics can improve the efficiency of ceramic waste forms. In this work, traditional garnet (Y1.2Nd1.8Fe5O12, YIG) and high‐entropy (HE) garnet (Y0.6Gd0.6Sm0.6Eu0.6Dy0.6Fe5O12, HEG) are synthesized through ignition and plasma sintering to form dense ceramic waste forms. The chemical stability of YIG and HEG was studied by using static leaching tests at pH = 3, 5, 7, 9, 11. The results indicate that acidic environments can increase the leaching rate of ceramics. Leaching behavior leads to a decrease in lattice volume, but the elements remain uniformly distributed. The leaching mechanism indicates that YIG and HEG are controlled by dissolution and surface effect in the early stage (1–7 days) of leaching. The leaching mechanism in the later stage (14–42 days) is characterized by diffusion control. The diffusion coefficient of long‐term leaching indicates that HEG is more suitable as the immobilization substrate for high‐level radioactive waste (HLW) than YIG.

Structural and Mechanical Properties of Doped Tobermorite.

As calcium silicate hydrate (C-S-H) is the main binding phase in concrete, understanding the doping behavior of impurity elements in it is important for optimizing the structure of cementitious materials. However, most of the current studies focus on cement clinker, and the doping mechanism of impurity elements in hydrated calcium silicate is not yet fully understood. The hydrated calcium silicate component is complex, and its structure is very similar to that of the tobermorite mineral family. In this study, the effects of three different dopants (Mg, Sr and Ba) on a representing structure of C-S-H-tobermorite-was systematically explored using densify functional theory (DFT) calculations. The calculations show that Mg doping leads to a decrease in lattice volume and causes obvious structure and coordination changes of magnesium-oxygen polyhedra. This may be the reason why high formation energy is required for the Mg-doped tobermorite. Meanwhile, doping only increases the volume of the Sr- and Ba-centered oxygen polyhedra. Specifically, the Mg-doped structure exhibits higher chemical stability and shorter interatomic bonding. In addition, although Mg doping distorts the structure, the stronger chemical bonding between Mg-O atoms also improves the compressive (~1.99% on average) and shear resistance (~2.74% on average) of tobermorillonite according to the elastic modulus and has less effect on the anisotropy of the Young's modulus. Our results suggest that Mg doping is a promising strategy for the optimized structural design of C-S-H.

Influence of synthetic temperature on structural and magnetic properties of Dy substituted Ni nanoferrite

ABSTRACT Dy substituted Ni ferrite nanoparticles with composition NiFe1.95Dy0.05O4 were synthesized by using the citric acid sol–gel auto combustion method. The samples were sintered at temperatures of 400°C, 700°C, and 900°C. The X-ray diffraction measurements clearly showed the formation of a cubic spinel structure along with a small orthoferrite phase for all the sintered samples. The crystallite size increases from 17.79 to 39.36 nm while the grain size increases from 50.70 nm to 83.05 nm. The lattice parameter and lattice volume decrease with increasing sintering temperature was observed. The Spinel ferrite structure of prepared samples has been confirmed from FTIR spectra. With increasing sintering temperature saturation magnetization increases from 25.80 emu/gm to 49.48 emu/gm while the coercivity value decreases from 207.95 Oe to 165.43 Oe. Increasing saturation magnetization and decreasing coercivity values with increasing sintering temperature make the synthesized nanoparticles suitable for high-density data storage devices.

Structure, thermal, optical and dielectric properties of SnO2 nanoparticles-filled HDPE polymer

The present study deals with the structural, thermal, optical and electrical properties of a new combination of nanocomposites with high-density polyethylene (HDPE) polymer and SnO2 nanoparticle filler. The structural and morphological change with SnO2 concentration (0.5, 1, 2, 3, 5, 10, 20 wt%) were investigated with Rietveld refinement of X-ray diffraction, FTIR, FESEM and Raman spectroscopy. It was found from the XRD refinement that a monotonic decrease in lattice volume and lattice paraments of HDPE with filler addition up to 5 wt % and non-uniform change in cell parameters at filler concentrations above 5 wt% due to the agglomeration of nanoparticles. The FTIR and Raman spectra analysis also supported the uniform dispersion of nanoparticles in the polymer below 5 wt% filler concentrations. The DSC and TGA studies proved that the addition of low concentrations of SnO2 nanofillers could significantly enhance the degradation temperature. The accelerated thermal aging studies using UV spectroscopy confirmed the improved thermal stability of nanocomposites. The optical and dielectric studies demonstrate the effective tailoring of these properties by changing the volume fraction of SnO2 nanoparticles. UV spectroscopy studies showed the higher UV-light shielding performance of nanocomposites than the pure HDPE polymer. The dielectric behaviour follows the percolation phenomenon and the critical volume fraction is found to be 1%. The rate of increase of dielectric permittivity of nanocomposites is around 17% with 20 wt % filler loading. The polymer nanocomposites with improved and tunable thermal, optical and dielectric properties benefit insulation and UV shielding applications.

Structural and magnetic phase transitions along with optical properties in GdMn1-xFexO3 perovskite

Herein, we report the structural evolution and the rich sequence of magnetic transitions in GdMn1–xFexO3 (x = 0, 0.3, and 0.5) synthesized through the sol-gel technique. Rietveld refinement of X-ray diffraction patterns reveals a structural transformation from O′ to O type orthorhombic one accompanied with a decrease in lattice volume when x increases from 0 to 0.5. The decrease in lattice volume is due to the presence of Mn4+ confirmed from X-ray photoelectron spectroscopy and photoluminescence (PL) studies. Such a structural transformation considerably reduces the Jahn-Teller distortion factor as indicated by Raman and PL spectra. The temperature dependent magnetization shows an increase in Néel temperature (TN) from ∼42 K for pristine GdMnO3 to almost room temperature for x = 0.5. Interestingly, we observe a spin reorientation temperature (TSR) at ∼270 and ∼253 K for x = 0.3 and 0.5, respectively. The mixed valency of Mn, i.e., Mn3+ and Mn4+ not only demonstrates a spin-glass (SG) behavior but also contributes toward the strong emission spectra irrespective of Fe concentration. The structural and magnetic properties of GdMnO3 after doping Fe suggest a possible way to achieve a better magnetoelectric coupling and modify the multiferroic property.

Tungsten bronze Li+ conductor LixSr1−0.5xTa2O6 (0

The lithiation of tungsten bronze oxide β-SrTa2O6 was accomplished by the solid state ion exchange of Sr2+ → 2Li+, which led to a solid solution of LixSr1−0.5xTa2O6 (x = 0–0.31). For the above conversion, β-SrTa2O6 was reacted with various amounts of Li2CO3 at 600 °C in air. With increasing x in LixSr1−0.5xTa2O6, an orthorhombic-to-tetragonal symmetry transition was observed along with a gradual decrease in lattice volume. As observed from scanning electron microscopy and transmission electron microscopy, the grains of LixSr1−0.5xTa2O6 phases with x = 0.17 and 0.25 were formed from columnar bundles aligned along the c-axis. Solid state 7Li nuclear magnetic resonance (NMR) spectroscopy revealed the presence of two different Li environments in LixSr1−0.5xTa2O6, and their respective populations. The ionic conductivity of LixSr1−0.5xTa2O6 was measured by ac impedance spectroscopy as functions of the temperature and composition x. Regardless of the composition, the conductivity of LixSr1−0.5xTa2O6 displayed an Arrhenius type temperature dependence, and the highest Li+ conductivity was found from x ≈ 0.17. At temperatures between 75 and 268 °C, the Li+ ionic conductivity of Li0.17Sr0.92Ta2O6 increased from 10−8.8 S/cm to 10−5.0 S/cm with an activation energy of 0.74 eV.

Synthesis and characterization of Yb doped Y2O3 nanopowder for transparent laser host ceramic materials

Pure yttrium oxide (Y2O3) and Yb doped Y2O3 (Yb: Y2O3) nanocrystalline powders were synthesized by the carbonate solution route which can be used in fabrication of transparent ceramics required for laser host application. Calcination time, temperature and pH were optimized to obtain well separated phase pure nanoparticles. The effect of Yb doping on structure of Y2O3 were studied by X-ray diffraction, transmission electron microscopy (TEM) and Raman spectroscopy. The phase structure was identified to be BCC for Y2O3 and distorted BCC for Yb: Y2O3 samples for 8 mole% doping of Yb. A decrease in lattice volume and homogeneous strain due to decrease in particle size was found to appear with Yb doping. Selected area electron diffraction (SAED) and High Resolution TEM (HRTEM) measurements investigations confirmed the BCC structure and found the nanoparticles to be in the range of 65-80 nm which decreased on Yb substitution. The Raman spectra explain the structural changes due to doping of Yb in Y2O3.

Rapid synthesis of Zn2+ doped SnWO4 nanowires with the aim of exploring doping effects on highly enhanced visible photocatalytic activities

In this work, we report on the rapid synthesis of Sn1−xZnxWO4 nanocrystals with the aim of tailoring their structural, electronic, and photocatalytic properties. The samples were carefully characterized by X-ray diffraction, transmission electron microscopy, inductive coupled plasma optical emission spectroscopy, UV-vis diffuse reflectance spectroscopy, and the Barrett–Emmett–Teller technique. The effects of Zn2+ doping in SnWO4 on the electronic structure and photogradation of methylene orange dye solution were investigated experimentally and theoretically. It was found that Zn2+ ions were homogeneously incorporated into the SnWO4 host lattice with a solubility of x = 0.060, which led to a monotonous decrease in lattice volume. With Zn2+ doping, SnWO4 nanocrystals showed a morphological alteration from irregular nanosheets to nanowires. Meanwhile, the BET surface areas were also greatly enlarged from 54 m2 g−1 to ∼100 m2 g−1. Contrary to the theoretical predictions of the quantum size effect, Zn2+ doped SnWO4 nanocrystals showed an abnormal band gap narrowing, which can be well-defined as a consequence of the balance of quantum size effect, lattice contraction, electronegativity, and surface defect centers. With well-controlled morphology, surface area, and electronic structure via Zn2+ doping, the photocatalytic performance of Sn1−xZnxWO4 nanocrystals was optimized at a Zn2+ doping level of x = 0.045.

Annealing of Anatase Titanium Dioxide under Hydrogen Atmosphere.

Anatase titanium dioxide was annealed under hydrogen atmosphere up to 800°C for several hours. The diffuse reflection spectra and X-ray diffraction were measured for the annealed powders. The changes in reflectance and conversion ratio to rutile depending on annealing conditions indicate that the contact of the powder with hydrogen in the temperature range of 400-700°C results in the formation of oxygen vacancies on the surface of the anatase powder. On the basis of the insignificant decrease in lattice volume depending on annealing temperature, there is a probability that other lattice defects could be formed. The transformation to the rutile phase was observed at temperatures higher than 650°C.

Structural and electrical characterisation of SrCe1−xYxOξ

The acceptor-doped perovskite proton conductor SrCe1−xYxOξ (x=0.025 to 0.20, ξ=3−x/2) has been prepared and characterised using X-ray diffraction and AC impedance spectroscopy, and the effect of the yttrium dopant concentration on structure and electrical properties has been investigated. X-ray diffraction studies show a decrease in lattice volume with increasing yttrium content. Electrical conductivity studies have been made as a function of oxygen partial pressure, and at a partial pressure of water vapour of 0.007 atm. The total conductivity has been separated into different components by fitting procedures and regions of ionic and p-type conduction have been identified. At 800°C and at the water vapour partial pressure of 0.007 atm, the ionic conductivity showed a maximum at a doping level of x=0.10, reaching a value of 5 mS/cm. The conductivity component appearing at low oxygen partial pressure, which according to recent studies may be regarded as protonic rather than n-type, decreased with doping, while the p-type component at high oxygen partial pressure increased. The relationship between the effect of doping on the conductivity and unit cell volume is discussed.

Time-resolved equatorial X-ray diffraction studies of skinned muscle fibres during stretch and release

Equatorial X-ray diffraction patterns were recorded from small bundles of one to three chemically skinned frog sartorius muscle fibres (time resolution 250 μs) during rapid stretch and subsequent release. In the relaxed state, the dynamic A-band lattice spacing change as a result of a 2 % step stretch (determined from the positions of the 10 and 11 reflections) resulted in a 21 % increase in lattice volume, while static studies of spacing and sarcomere length indicated than an increase in volume of ⩾50 % for the same length change. In rigor, stretch caused a lattice volume decrease which was reversed by a subsequent release. In activated fibres (pCa 4.5) exposed to 10 mM 2,3-butanedione 2-monoxime (BDM), stretch was accompanied by a lattice compression exceeding that of constant volume behaviour, but during tension recovery, compression was partially reversed to leave a net spacing change close to that observed in the relaxed fibre. In the relaxed state, spacing changes were correlated with the amplitude of the length step, while in rigor and BDM states, spacing changes correlated more closely with axial force. This behaviour is explicable in terms of two components of radial force, one due to structural constraints as seen in the relaxed state, and an additional component arising from cross-bridge formation. The ratio of axial to radial force for a single thick filament resulting from a length step was four in rigor and BDM, but close to unity for the relaxed state.