Average Lattice Constant Research Articles

Effect of Nb substitution on structural, electrical and electrochemical properties of LiTi2(PO4)3 as electrolyte materials for lithium ion batteries

ABSTRACTThe NASICON (Na Super Ionic CONductors)-type materials are good ionic conductors when serving as solid electrolytes for lithium–ion batteries. In this paper, Nb-doped LiTi2(PO4)3 has been synthesized by solid-state reaction method and the structural, vibrational and dielectric studies are systematically investigated. The X-ray diffraction conforms that the Nb-doped LiTi2(PO4)3 compound has NASICON structure, i.e. rhombohedral with space group R-3c. The average crystallite size and lattice constant are increased with dopant concentration. The grain sizes of the synthesized compounds are investigated by scanning electron microscope and it is found to be in the range of 5 μm. From Fourier-transform infrared spectroscopy spectra, stretching vibrations of P-O-P bond are identified in the region of 700–750 cm−1. AC electrical study is carried out by exploiting the impedance and dielectric spectroscopy. The activation energy increases with dopant concentration since ion diffusion becomes easy as the volume fraction of the grain increases. Non-Debye behavior of conductivity relaxation is reflected in the modulus analysis.

Flattening and manipulation of the electronic structure of h-BN/Rh(111) nanomesh upon Sn intercalation

We have deposited Sn on corrugated hexagonal boron nitride (h-BN) nanomeshs formed on Rh(111) and found that Sn atoms are intercalated between h-BN and Rh, flattening the h-BN. Our reflection high-energy electron diffraction (RHEED) analysis showed that the average in-plane lattice constant of h-BN increases due to the loss of the corrugation. Furthermore, electronic structure measurements based on angle-resolved photoemission spectroscopy (ARPES) showed that the h-BN π band width increases significantly while the σ band width does not change as much. These behaviors were partly different from previous reports on the intercalation of h-BN/Rh system. Our results offer a novel, simple method to control the electronic structure of h-BN.

Investigation of Thermodynamic Properties of Zirconia Thin Films by Statistical Moment Method

The moment method in statistical (SMM) dynamics is used to study the thermodynamic quantities of ZrO2 thin films taking into account the anharmonicity effects of the lattice vibrations. The average lattice constant, thermal expansion coefficient and specific heats at the constant volume of ZrO2 thin films are calculated as a function of temperature, pressure and thickness of thin film. SMM calculations are performed using the Buckingham potential for the ZrO2 thin films. In the present study, the influence of temperature, pressure and the size on the thermodynamic quantities of ZrO2 thin film have been studied using three different interatomic potentials. We discuss temperature and thickness dependences of some thermodynamic quantities of ZrO2 thin films and we compare our calculated results with those of the experimental results.

Synthesis and Optical Properties of Pb Doped ZnO Nanoparticles

This article deals with the structural and optical characterization of lead-doped zinc oxide nanoparticles synthesized by precipitation method. X-ray diffraction study confirmed the substitution of Pb dopant without disturbing the basic wurtzite structure of zinc oxide. The average crystallite size, lattice constants, and unit cell volume also increased up to 10% of lead doping. The energy gap of the samples was determined from the ultraviolet-visible absorption spectrum as well as Tauc’s plot which infers that the energy gap decreases with the increase of lead content. Fourier Transformation Infra Red spectrum confirmed the lead dopant through peak shifting from 437–549cm−1. Photoluminescence spectrum also defines the leads dopant by means of intensity increase. Scanning electron microscope study also confirmed the existence of particles in nanometer size and it witnessed the microstructure transformation from nanoparticles to the rod-like structure on 10 (wt.%) lead doping.

A correlated structural and electrical study of manganese ferrite nanoparticles with variation in sintering temperature

Manganese ferrite nanoparticles were prepared by chemical co-precipitation method. Metal chlorides and sodium hydroxide were used as precursor. The spinel phase formation of the prepared samples was confirmed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). From the XRD data, the average crystallite size and lattice constant were calculated. FTIR spectra reveal the characteristic absorption bands of spinel ferrite due to M-O stretching vibrations in tetrahedral and octahedral sites. Manganese ferrite nanoparticles were further given sintering. The effect of sintering at different temperatures on the structural properties such as XRD, FTIR and electrical properties such as dielectric constant, dielectric loss and ac-conductivity was studied. Possible mechanism of structural changes and observed electrical behavior due to sintering is being discussed. A strong correlation has also been observed in the results obtained from different characterization techniques.

Electrochemical Scanning Tunneling Microscopic Study of the Potential Dependence of Germanene Growth on Au(111) at pH 9.0.

Germanene is a 2D material whose structure and properties are of great interest for integration with Si technology. Preparation of germanene experimentally remains a challenge because, unlike graphene, bulk germanene does not exist. Thus, germanene cannot be directly exfoliated and is mostly grown in ultrahigh vacuum. The present report uses electrodeposition in an aqueous HGeO3- solution at pH 9. Germanene deposition has been limited to 2-3 monolayers, thus greatly restricting many applicable characterization methods. The in situ technique of electrochemical scanning tunneling microscopy was used to follow Ge deposition on Au(111) as a function of potential. Previous work by this group at pH 4.5 suggested germanene growth, but no buffer was used, resulting in change in surface pH. The addition of borate buffer to create pH 9.0 solution has reduced hydrogen formation and stabilized the surface pH, allowing systematic characterization of germanene growth versus potential. Initial germanene nucleated at defects in the Au(111) herringbone (HB) reconstruction. Subsequent growth proceeded down the face-centered cubic troughs, slowly relaxing the HB. The resulting honeycomb (HC) structure displayed an average lattice constant of 0.41 ± 0.06 nm. Continued growth resulted in the addition of a second layer on top, formed initially by nucleating around small islands and subsequent lateral 2D growth. Near atomic resolution of the germanene layers displayed small coherent domains, 2-3 nm, of the HC structure composed of six-membered rings. Domain walls were based on defective, five- and seven-membered rings, which resulted in small rotations between adjacent HC domains.

Self-assembled flower-like microstructure in Zn 1-x Cd x O nanoparticles

The structural and optical characterization of cadmium-doped zinc oxide nanoparticles synthesized by precipitation method was studied. X-ray diffraction study confirmed the substitution of cadmium dopant without disturbing the basic wurtzite structure of zinc oxide. The average crystalline size, lattice constants and unit cell volume also increased up to 4% of cadmium doping. Energy gaps of the samples were determined from the ultraviolet-visible absorption spectrum as well as Tauc's plot which infers that the energy gap decreases with the increase of cadmium content. Fourier transformation infrared spectrum confirms the cadmium dopant through peak shifting from 485 to 563 cm−1. Photoluminescence spectrum also defines the cadmium dopant by intensity increase. The broad Raman peak at 437 cm−1 indicates that the wurtzite structure of zinc oxide is weakened by 5% cadmium doping. Field emission scanning electron microscope study also confirms the existence of particles in nanometer size and it indentifies the microstructure transformation from nanoparticles to jasmine flower-like structure on 5% cadmium doping.

Time of Growth Dependent of ZnO-Nanorods by Self-Assembly Methods and its Structural Properties

ZnO-nanorods (ZnO-Nrs) have been successfully prepared on glass substrate using self-assembly method by varying deposition time. Zn acetate dehydrate and 2-methoxyethanol was used as raw material and solvent respectively (for ZnO seed layer preparation), meanwhile Zn nitrate hexahydrate and hexametylenetetramine (HMTA) dissolved in deionized water used as solution growth of ZnO-Nanorods (ZnO-Nrs). In this work, deposition times of ZnO-Nrs were varied by 120 min, 150 min, 180 min and 210 minutes at 100°C of annealing temperature. In order to investigate the physical properties of resulting ZnO, several measurements such as x-ray diffraction (XRD), ultra-violet visible spectroscopy and scanning electron microscopy (SEM) were carried out. Based on ZnO nanorods SEM image with varying time depositions, seems that increasing deposition time the nanorod size decrease but when the time reach 210 min, the average size of nanorods turned back increase. From XRD measurement, the average grain size and lattice constant (c) which is assemble the nanorod structure and lattice constant (c) was determined by Debye-Scherrer formula and Bragg law’s respectively. The growth process of ZnO nanorod by 180 min time deposition was known as an appropriate time to produce ZnO nanorods with high crystal quality due to sharp peak intensity of XRD spectrum.

Broadband and omnidirectional light harvesting enhancement in photovoltaic devices with aperiodic TiO2 nanotube photonic crystal

Design of more effective broadband light-trapping elements to improve the light harvesting efficiency under both normal and tilted light for solar cells and other photonic devices is highly desirable. Herein we present a theoretical analysis on the optical properties of a novel TiO2 nanotube aperiodic photonic crystal (NT APC) following an aperiodic sequences and its photocurrent enhancement effect for dye-sensitized solar cells (DSSCs) under various incidence angles. It is found that, compared to regular PC, the designed TiO2 NT APC owns broader reflection region and a desired omnidirectional reflection (ODR) bandgaps, leading to considerable and stable photocurrent enhancement under both normal and oblique light. The effects of the structural parameters of the TiO2 NT APC, including the average lattice constant and the common sequence difference, on the optical properties, ODR bandgaps and absorption magnification of the integrated DSSCs are investigated in detail. Moreover, the angular dependence of photocurrent enhancement and angular compensation effect of such TiO2 NT APCs are also provided to offer a guidance on the optimum structural parameters design under different engineering application conditions.

Molecular dynamics study onβ-phase vanadium monohydride with machine learning potential

The formalism to construct the machine learning potentials (MLPs) is presented. We introduce the spilling factor for the simultaneous error estimation and the recursive bisection method for the reduction of the computational cost. The formalism is applied for the $\ensuremath{\beta}$-phase vanadium monohydride. The first-principles calculations based on density functional theory (DFT) are used to prepare the sample data set from which the MLP for the vanadium monohydride (VH) system is constructed. In the molecular dynamics simulation with the MLP, the time-averaged structure of $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{VH}$ is predicted correctly to be the body-centered tetragonal structure with the octahedral $(O)$ site occupation of H. The average lattice constants are in good agreement with the experimental data which are not able to be reproduced by the static DFT calculation. The $O$-site occupation of H observed in the average structure is, however, a saddle point on the potential-energy surface, and the actual hydrogen occupation is found to be the $4T$ configuration.

Measurement of InAsBi mole fraction and InBi lattice constant using Rutherford backscattering spectrometry and X-ray diffraction

Several 1 μm thick, nearly lattice-matched InAsBi layers grown on GaSb are examined using Rutherford backscattering spectrometry and X-ray diffraction. Random Rutherford backscattering measurements indicate that the average Bi mole fraction ranges from 0.0503 to 0.0645 for the sample set, and ion-channeling measurements indicate that the Bi atoms are substitutional. The X-ray diffraction measurements show a diffraction sideband near the main (004) diffraction peak, indicating that the Bi mole fraction is not laterally uniform in the layer. The average out-of-plane tetragonal distortion is determined by modeling the main and sideband diffraction peaks, from which the average unstrained lattice constant of each sample is determined. By comparing the Bi mole fraction measured by random Rutherford backscattering with the InAsBi lattice constant for the sample set, the lattice constant of zinc blende InBi is determined to be 6.6107 Å.

Charge compensation and electrostatic transferability in three entropy-stabilized oxides: Results from density functional theory calculations

Density functional theory calculations were carried out for three entropic rocksalt oxides, (Mg0.1Co0.1Ni0.1Cu0.1Zn0.1)O0.5, termed J14, and J14 + Li and J14 + Sc, to understand the role of charge neutrality and electronic states on their properties, and to probe whether simple expressions may exist that predict stability. The calculations predict that the average lattice constants of the ternary structures provide good approximations to that of the random structures. For J14, Bader charges are transferable between the binary, ternary, and random structures. For J14 + Sc and J14 + Li, average Bader charges in the entropic structures can be estimated from the ternary compositions. Addition of Sc to J14 reduces the majority of Cu, which show large displacements from ideal lattice sites, along with reduction of a few Co and Ni cations. Addition of Li to J14 reduces the lattice constant, consistent with experiment, and oxidizes some of Co as well as some of Ni and Cu. The Bader charges and spin-resolved density of states (DOS) for Co+3 in J14 + Li are very different from Co+2, while for Cu and Ni the Bader charges form continuous distributions and the two DOS are similar for the two oxidation states. Experimental detection of different oxidation states may therefore be challenging for Cu and Ni compared to Co. Based on these results, empirical stability parameters for these entropic oxides may be more complicated than those for non-oxide entropic solids.

Density functional study for crystalline structures and electronic properties of Si1−xSnx binary alloys

We have carried out density functional theory (DFT) calculation for Si1−xSnx alloy and investigated the effect of the displacement of Si and Sn atoms with strain relaxation on the lattice constant and E–k dispersion. We calculated the formation probabilities for all atomic configurations of Si1−xSnx according to the Boltzmann distribution. The average lattice constant and E–k dispersion were weighted by the formation probability of each configuration of Si1−xSnx. We estimated the displacement of Si and Sn atoms from the initial tetrahedral site in the Si1−xSnx unit cell considering structural relaxation under hydrostatic pressure, and we found that the breaking of the degenerated electronic levels of the valence band edge could be caused by the breaking of the tetrahedral symmetry. We also calculated the E–k dispersion of the Si1−xSnx alloy by the DFT+U method and found that a Sn content above 50% would be required for the indirect–direct transition.

Avalanches, plasticity, and ordering in colloidal crystals under compression.

Using numerical simulations we examine colloids with a long-range Coulomb interaction confined in a two-dimensional trough potential undergoing dynamical compression. As the depth of the confining well is increased, the colloids move via elastic distortions interspersed with intermittent bursts or avalanches of plastic motion. In these avalanches, the colloids rearrange to minimize their colloid-colloid repulsive interaction energy by adopting an average lattice constant that is isotropic despite the anisotropic nature of the compression. The avalanches take the form of shear banding events that decrease or increase the structural order of the system. At larger compression, the avalanches are associated with a reduction of the number of rows of colloids that fit within the confining potential, and between avalanches the colloids can exhibit partially crystalline or anisotropic ordering. The colloid velocity distributions during the avalanches have a non-Gaussian form with power-law tails and exponents that are consistent with those found for the velocity distributions of gliding dislocations. We observe similar behavior when we subsequently decompress the system, and find a partially hysteretic response reflecting the irreversibility of the plastic events.

Magnetic and Dielectric Properties of Polymer-Coated Ni0.5Co0.3Cu0.2Fe2O4 Nanostructures

Ni0.5Co0.3Cu0.2Fe2O4 and Ni0.5Co0.3Cu0.2Fe2 O4/polyethylene glycol (PEG) were synthesized by using the co-precipitation method. The structural, morphological, magnetic, and dielectric properties of the products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), vibrating sample magnetometry (VSM), and Agilent dielectric probing, respectively. XRD analysis confirms the spinel structure of samples with an average particle size of 13 and 21 nm for Ni0.5Co0.3Cu0.2Fe2O4 and Ni0.5Co0.3Cu0.2Fe2O4/PEG, respectively. FTIR analysis shows the presence of two vibrational bands between 400 and 600 cm−1 corresponding to lattice vibrations in tetrahedral and octahedral sites. FESEM images indicate the formation of nano-sized particles. The results of VSM imply that both samples show a ferromagnetic behavior. The complex dielectric permittivity of the samples was changed after PEG coating. The real part of the permittivity varied from 4.1 to around 5.7 by adding PEG. Adding PEG polymer caused variation in the average crystallite size, lattice constant, and magnetic coercivity.

Characterization of neutron-irradiated HT-UPS steel by high-energy X-ray diffraction microscopy

This paper presents the first measurement of neutron-irradiated microstructure using far-field high-energy X-ray diffraction microscopy (FF-HEDM) in a high-temperature ultrafine-precipitate-strengthened (HT-UPS) austenitic stainless steel. Grain center of mass, grain size distribution, crystallographic orientation (texture), diffraction spot broadening and lattice constant distributions of individual grains were obtained for samples in three different conditions: non-irradiated, neutron-irradiated (3dpa/500 °C), and irradiated + annealed (3dpa/500 °C + 600 °C/1 h). It was found that irradiation caused significant increase in grain-level diffraction spot broadening, modified the texture, reduced the grain-averaged lattice constant, but had nearly no effect on the average grain size and grain size distribution, as well as the grain size-dependent lattice constant variations. Post-irradiation annealing largely reversed the irradiation effects on texture and average lattice constant, but inadequately restored the microstrain.

Characterization and Evaluation of Property of Columbite–MgNb2O6 Synthesized by Chemical Route

A simple chemical route is used to successfully synthesized magnesium niobate (MgNb2O6: MN) nano ceramic material at various processing temperatures. The initial phase formation characterization has been studied by thermal analysis for pure MN formation using TG–DT analysis. The synthesized powder materials are characterized by X-ray diffraction (XRD), Raman spectra and energy dispersive X-ray (EDX). The formation of MN phase of powder samples is determined from the XRD. Average lattice constants of MN ceramic sample are measured from XRD data. The formation of MN phase of synthesized samples is also identified by Raman spectra. The chemistry is measured by EDX analysis. The photoluminescence spectra shows a broad blue emission band centered at 426 nm and the band gap energy is 2.19 eV as measured by UV–Vis spectroscopy using Tauc equation. The photoluminescence and optical property of synthesized MN ceramic material are studied at room temperature.

Structure and composition effects on electrical and optical properties of sputtered PbSe thin films

Lead selenide (PbSe) thin films were grown on Si (111) substrates using magnetron sputtering, and the structure and composition effects on the photoelectric and optical properties of the sputtered PbSe thin films were studied using field emission scanning electron microscope, energy dispersive X-ray detector, X-ray diffraction, X-ray photoelectron spectroscopy, physical property measurement system and Fourier transform infrared spectroscopy. The optical band gaps of all the sputtered PbSe thin films ranged from 0.264eV to 0.278eV. The PbSe thin film prepared with oxygen flux 1.0sccm, deposition time 240min, sputtering power 150W and substrate temperature 150°C showed the highest resistance change rate under illumination, about 84.47%. The variation trends of the photoelectric and optical properties with the average crystal size, lattice constant, oxygen content and lattice oxygen percentage were similar, respectively. The sputtered PbSe thin films showed poor photoelectric sensitivity, when the average crystal size was similar to the Bohr radius (46nm), while the photoelectric sensitivity increased almost linearly with the oxygen content in the thin films, indicating that both deviating the average crystal size from the Bohr radius and increasing the oxygen content are two direct and effective ways to obtain high photoelectric sensitivity in PbSe thin films.

Microstructural investigation of plastically deformed Ti20Zr20Hf20Nb20Ta20 high entropy alloy by X-ray diffraction and transmission electron microscopy

The microstructure evolution in body-centered cubic (bcc) Ti20Zr20Hf20Nb20Ta20 high entropy alloy during quasi-static compression test was studied by X-ray line profile analysis (XLPA) and transmission electron microscopy (TEM). The average lattice constant and other important parameters of the microstructure such as the mean crystallite size, the dislocation density and the edge/screw character of dislocations were determined by XLPA. The elastic anisotropy factor required for XLPA procedure was determined by nanoindentation. XLPA shows that the crystallite size decreased while the dislocation density increased with strain during compression, and their values reached about 39nm and 15×1014m−2, respectively, at a plastic strain of ~20%. It was revealed that with increasing strain the dislocation character became more screw. This can be explained by the reduced mobility of screw dislocations compared to edge dislocations in bcc structures. These observations are in line with TEM investigations. The development of dislocation density during compression was related to the yield strength evolution.

Rechargeable Sodium-Ion Battery: High-Capacity Ammonium Vanadate Cathode with Enhanced Stability at High Rate.

Sodium-ion battery (NIB) cathode performance based on ammonium vanadate is demonstrated here as having high capacity, long cycle life and good rate capability. The simple preparation process and morphology study enable us to explore this electrode as suitable NIB cathode. Furthermore, density functional theory (DFT) calculation is envisioned for the NH4V4O10 cathode, and three possible sodium arrangements in the structure are depicted for the first time. Relevant NIB-related properties such as average voltage, lattice constants, and atomic coordinates have been derived, and the estimated values are in good agreement with the current experimental values. A screening study shows ammonium vanadate electrodes prepared on carbon coat onto Al-current collector exhibits a better electrochemical performance toward sodium, with a sustained reversible capacity and outstanding rate capability. With the current cathode with nanobelt morphology, a reversible capacity of 190 mAh g(-1) is attained at a charging rate of 200 mA g(-1), and a stable capacity of above 120 mAh g(-1) is retained for an extended 50 cycles tested at 1000 mA g(-1) without the addition of any expensive electrolyte additive.