Distortion Of Crystal Lattice Research Articles

Convolutional neural network for sapphire ingots defect detection and classification

Optical homogeneity detection can be brought into play for quality control of sapphire substrate, sapphire mobile phone screen, and sapphire window material. By detecting the optical homogeneity of the sapphire crystal, the crystal lattice distortion inside the crystal can be evaluated non-destructively and intuitively. However, due to the small birefringence coefficient of sapphire crystals, it is difficult to detect the optical homogeneity of sapphire ingots through the conventional setup. In this work, we detected the optical homogeneity of the sapphire ingot using the Focused Polarization Interference (FPI) method also known as Conoscopic Birefringence Interferometry. The main principle of this technique is that the stress induced by the lattice distortion may cause the variation of the crystal birefringence which leads to the formation of the polarization interference patterns. To quantitatively evaluate the pattern deformation, we used pattern recognition technique. However, the main issue in pattern recognition and notably images classification problems is image feature extraction and image encoding. To solve the above problem, here we showed and compared different approaches: Bag of features, ResNet-50, AlexNet, VGG16, and GoogleNet pre-trained convolutional neural network (CNN) models. The reliability, practicality, and verification of the proposed models, in this work, is according to the detection measures use accuracy, confusion matrix, and Area Under the Curve (AUC). The Bag of features model achieved the classification accuracy of 94.3%, while the ResNet-50 pre-trained convolutional neural network achieved 97.6%. The findings show that ResNet-50 is capable of correctly classifying the samples from the datasets with high true fraction value and low false positive followed by AlexNet as compare to other models like VGG16 and GoogleNet. Finally, the proposed models have been in contrast with the well-known chemical etching method. The results showed that the time required to etch one sample using chemical etching is about 10 h, while by using the proposed models, we can detect and classify the whole dataset within 80 min and 27 s. The proposed pre-trained convolutional neural network models based on sapphire crystal defects classification would potentially serve as a new tool for predicting the quality inspection-based on crystal growth technology. • Optical homogeneity detection can be used for quality control of sapphire substrate. • The small birefringence coefficient of sapphire crystals. • It is difficult to detect the optical homogeneity of sapphire ingots through the conventional setup. • Focused Polarization Interference (FPI) method, so-called Conoscopic Birefringence Interferometry is used. • Pre-trained convolutional neural network (CNN) models evaluate and classify the patterns deformations.

Mechanochemical synthesis of ternary heterojunctions TiO2(A)/TiO2(R)/ZnO and TiO2(A)/TiO2(R)/SnO2 for effective charge separation in semiconductor photocatalysis: A comparative study

TiO2, ZnO, and SnO2 metal oxides were synthesized by the sol-gel method and heterojunctions were fabricated by combining TiO2 with either ZnO or SnO2 in a 1:1 ratio using mechanochemical ball milling process. The ball milling process promotes phase transition of TiO2 from anatase to rutile and yields ternary heterojunction of the type TiO2(A)/TiO2(R)/ZnO and TiO2(A)/TiO2(R)/SnO2 (A-anatase and R-rutile). These ternary heterojunctions were characterized by various analytical techniques and its photocatalytic efficiency is evaluated using 4-Chloro Phenol as a model compound under UV and solar light. The enhanced catalytic activity of TiO2(A)/TiO2(R)/ZnO heterojunction is attributed to the formation of Ti3+-Vo defect states which leads to the efficient charge carrier separation. During the ball milling process severe crystal deformation takes place in TiO2 and ZnO lattices by creating crystal lattice distortion which leads to the formation of defects due to valency mismatch between Ti4+ and Zn2+. A mechanistic pathway is proposed for the enhanced photocatalytic activity of the ternary heterojunctions.

Structural properties of MeF2 (Me=Ca, Sr, Ba) crystals doped with rare-earth ions RE3+/ RE2+: ab initio route

In this paper, we simulated the structural properties of the cubic impurity centers RE3+/RE2+ (RE = Rare earth) in fluorites crystals MeF2 (Me = Ca, Sr, Ba) by ab initio route. Doping fluorite crystals with the rare-earth ion RE3+/RE2+, this replaces the cation Me2+ and determines distortions of the MeF2 crystal lattice near the impurity center. These distortions characterized by radial and angular displacements of anions were investigated by ab initio method. We have employed the MO LCAO approach, in the frame of DFT method as it is implemented in the CRYSTAL17 software for periodic systems, using the hybrid functional PBE0. Since the main contribution to the crystal field on the rare-earth impurity ions comes from its nearest neighbors, the distance “rare-earth ion – ligand” and the radial and angular coordinates of the RE3+/RE2+ ions at several coordination spheres of anions near the impurity centers are calculated. Also, the changes in the local compressibility of the cationic and anionic sublattice next to the impurity ion are determined. The obtained results were discussed, compared with available experimental data and other theoretical results, and the agreement is quite satisfactory.

Untangling the effects of octahedral rotation and ionic displacements on the electronic structure of BiFeO3

The electronic structure and related properties of perovskites ${\mathrm{ABO}}_{3}$ are strongly affected by even small modifications in their crystalline structure. In the case of ${\mathrm{BiFeO}}_{3}$, variations in the octahedral rotations and ionic displacements lead to significant changes in the band gap. This effect can possibly explain the wide range of values (2.5--3.1 eV) reported in the literature, obtained from samples of varied structural qualities, including polycrystalline films, epitaxial films grown by pulsed-laser deposition and molecular beam epitaxy, nanowires, nanotubes, and bulk single crystals. Using hybrid density-functional calculations, we investigate the dependence of the electronic structure on the crystal lattice distortions of the ferroelectric-antiferromagnetic ${\mathrm{BiFeO}}_{3}$, disentangling the effects of the ferroelectric ionic displacements and the antiferrodistortive octahedral rotations on the band gap and the band-edge positions. The band gap is shown to vary from 3.39 eV for the rhombohedral ground-state (R3c) structure down to 1.58 eV for the perfect cubic (Pm$\overline{3}$m) structure, with changes in the conduction band being much more prominent than in the valence band. The gap varies linearly with the ferroelectric ionic displacements, but nonlinearly with the octahedral rotations around the pseudocubic [111${\mathrm{]}}_{c}$ axis, and this is explained in terms of the different interactions between Bi $6s, 6p$, Fe $3d$, and O $2p$ bands. We argue that such large variation of the band gap with structural changes may well explain the large scattering of the reported values, especially if significant deviations from the equilibrium crystal structure are found near domain boundaries, extended defects, or grain boundaries in polycrystalline films.

Spontaneous chiral self-assembly of CdSe@CdS nanorods

Spontaneous chiral self-assembly of CdSe@CdS nanorods

Structural, optical and magnetic properties of Co(Cobalt) doped SnO2 nanoparticles by one stepmethod

Cobalt doped SnO2 nanoparticles were prepared for different molar concentration 2%, 4% & 6% of Co by Chemical co precipitation method. The prepared samples were characterized by X-ray diffraction (XRD), UV-visible absorption spectra, Photoluminescence (PL), High Resolution transmission electron microscopy (HRTEM) and Vibrating sample magnetometer for their Structural, Optical and Magnetic Properties. The doping concentration of Co induces crystal phase, crystallite size, lattice distortion, optical and magnetic properties were investigated. XRD Results showed that Co2+ replaces Sn4+ in the crystal lattice of SnO2, which enhanced the growth of crystallite size and suppressed the transformation from anatase to rutile phase due to lattice distortion produced in SnO2. The UV absorption studies concluded the band gap of Co doped SnO2 nanoparticles decreased from 3.79 eV to 3.62 eV in visible region. PL spectra exhibit only a broad emission peak in the range of 420 nm to 540 nm and excitation is observed at the wavelength of 385 nm. New energy levels are not formed in the band structure to produce new emission due to Co doping and also indicates that the substitution of Co2+ ions for Sn4+ ions without the formation of other additional energy levels. Due to increasing Co concentration in SnO2, the emission energies are decreasing the peak intensities. An efficient method for inducing the ferromagnetic behavior from increasing the Co concentration from 2% to 6 % was known from the magnetization versus magnetic field (M–H) curves at room temperature of the Co doped SnO2 samples. The dominant magnetic interaction between Co ions, and hence, the ferromagnetic behaviour increases for increase in Co2+ doping concentration.Consequently, to achieve the good ferromagnetic character in these materials, the concentration of Co dopant has to be properly optimized.

Description of grain boundary structure and topology in nanocrystalline aluminum using Voronoi analysis and order parameter

Grain boundaries (GB) have a significant impact on mechanical, physical properties and microstructure of polycrystalline materials. Their studies are necessary for designing materials of improved properties. We present molecular dynamics based studies of grain boundary in nanocrystalline aluminum. A Voronoi tessellation based method (Voronoi analysis, VA) and order parameter approach were used for describing structure and topological features in nanocrystalline aluminum. We are portraying new functionality and usefulness of VA combined with order parameter (OP) to picturing structure nature of grain boundary (GB) and its order given in form of configuration entropy. Voronoi analysis unveiled sub-nanoscale topological features contributing to GB which correspond to lattice distortions and liquid-like GB behavior. Grouping of Voronoi cell indices to a crystal lattice distortion group was made together with corresponding to them OP values. Two complementary methods used in this work provide new information and open new possibilities for studying structure and properties of nanomaterials.

Impact of Al3+ incorporation on microstructural pattern, optical and electrical behaviors of PbS:Al3+ films from an alkaline chemical bath

The great improvement in electrical conduction of PbS films is still critical for the application of PbS-infrared detectors and solar cells so far. The incorporation of certain ions to PbS is proved effective for the improvement in electrical conduction. Herein a series of face-centered cubic Al3+-incorporated PbS (PbS:Al3+) films with improved electrical conduction are synthesized on p-type Si(100) substrates from an alkaline chemical bath. The impact of Al3+ molar concentration (CAl) is intensively studied on the microstructural pattern, optical and electrical behaviors of the films. The mechanism of the formation of highly crystallized PbS:Al3+ in alkaline chemical bath is also proposed. All the PbS:Al3+ films are slightly rich in Pb. The strong coordination between Pb2+ and organic triethanolamine molecules plays a key role in the formation of highly crystallized PbS:Al3+. The incorporated Al3+ weakens and even destroys the preferred 〈200〉 orientation of the films due to the enhanced crystal lattice distortion. The film’s resistivity is firstly reduced and then increased with increase in CAl, and the near-infrared optical absorption edge slightly blueshifts and then redshifts. The change in resistivity with increase in CAl can be explained by the substitution of Pb2+ by Al3+ and the change in crystallite size, and the slight blue and red shift in optical edge with increase of CAl is mainly attributed to the increase and the decrease in tensile stress of the films caused by the Al3+ incorporation into PbS, respectively.

Форма лінії дислокації в полі стохастичних зсувних напружень

The shape of the dislocation line in the stochastic shear stress field in the glide plane was studied using the method of discrete dislocation dynamics. Stochastic shear stresses can occur due to the distortion of the crystal lattice. Such distortion may exist, for example, in a solid solution. Different atoms in a solid solution induce atomic size misfit and elastic modulus misfit into crystal lattice. These misfits result in crystal lattice distortions which varies spatially. The distortions are the origin of internal stresses in the lattice. Such internal stress in certain location has stochastic value normally distributed. The particular case of such stresses is shear stress distribution in the glide plane. The special method was developed to model such stress distribution. The stochastic shear stress field results in movement of different segments of dislocation line to form its equilibrium shape. The important characteristic parameters of the equilibrium shape can be measured by numerical methods. This shape also includes a "long-wavelength" component that has a non-zero amplitude and was formed without thermal activation. The shape of the dislocation line determines to some extent the yield strength of the material. Thus, the study of dislocation line shape and modeling its formation in the field of stochastic shear stresses can help to determine the yield strength of multicomponent alloys, especially multi-principal element alloys. Keywords: dislocation, discrete dislocation dynamics, shear stresses.

Phase transition induced morphotropic phase boundary behavior and the electric properties in strontium modulated Bi4.5Na0.5Ti4O15 lead-free ceramics

Lead-free (Bi0.5Na0.5)1-xSrxBi4Ti4O15 ceramics (x = 0–0.9) are fabricated by solid state reaction process. XRD analysis shows the symmetry divergence from tetragonal to orthorhombic phase accompanied by morphotropic phase boundary with increasing strontium content. Raman spectra confirm the incorporation of strontium into (Bi2.5Na0.5Ti4O13)2- layers. SEM graphs exhibit the typical plate-like morphology with regular variation of grain size and crystallization as strontium increases. Multistage ferroelectric transition is observed with x = 0.2–0.4. Piezoelectric performance measurements present the well thermal stability at x = 0.4. The dielectric properties display a shifting of Curie temperature towards low temperature with increasing strontium ions. It can be due to the crystal lattice distortion by larger radius of strontium and the increasing tolerance factor. ac conductivity and impedance measurements suggest that electron hopping mainly contributes to the low temperature region. Ionization conductivity by oxygen vacancy migration including first-ionization and double-ionization plays the dominating role in the middle and high temperature region. The controllable properties indicate the potential applications for electric devices of (Bi0.5Na0.5)1-xSrxBi4Ti4O15 ceramic.

Effects of Ni2+, Zr4+, or Ti4+ doping on the electromagnetic and microwave absorption properties of CaMnO3 particles

Although CaMnO3 has been widely studied and used for its thermoelectric properties and giant magnetoresistance effect, little information exists about its application for microwave absorption. In this study, we synthesized CaMnO3, CaNi0.05Mn0.95O3 CaTi0.05Mn0.95O3 and CaZr0.05Mn0.95O3 with an orthorhombic system using a simple high-temperature solid-phase method. The minimum reflection loss value and effective absorption bandwidth could be efficiently improved due to the enhanced match complex permittivity produced after the Ni, Ti or Zr ions were substituted for Mn ions in CaMnO3. The minimum reflection loss value increases to −39.7 dB from −14.1 dB and the effective absorption bandwidth increases to 4.9 GHz from 2.7 GHz. The magnetic loss results only in a negligible influence on the microwave absorption. The enhancement of microwave absorption properties was primarily due to the stronger polarization effect. When Ni2+, Ti4+, or Zr4+ is introduced in the CaMnO3 lattice, the charge balance is broken, and the crystal lattice distortion increases because of the substitutive ions, interstitial ions, oxygen vacancy and exchange effect of Mn3+~Mn4+. The results indicate that CaMnO3 with reasonable doping at the Mn-site could achieve excellent microwave properties of wide bandwidth, high-efficiency absorption, and adjustable response frequency.

The Influence of Interstitial Carbon and Oxygen on Grain Boundary Diffusion in Nickel and Silver

The paper investigates the influence of interstitial carbon and oxygen atoms on their diffusion along the , and tilt grain boundaries in face-centered cubic nickel and silver. It is shown that in most cases, the impurity addition leads to the growth in the self-diffusion coefficient along the grain boundaries due to the crystal lattice distortion near the impurity atoms, thereby causing the additional lattice distortion and free volume along the grain boundaries. And the lower the initial free volume on the grain boundary, the stronger is the effect from impurities on the grain boundary diffusion. In this regard, the highest and lowest effects from the impurities are observed for the and tilt grain boundaries, respectively. It is found that the influence of interstitial carbon on the grain boundary diffusion is stronger than that of oxygen.

2D real space visualization of d values in polycrystalline bulk materials of different hardness

Conventional X-ray diffraction measurements provide some average structural information, mainly on the crystal structure of the whole area of the given specimen, which might not be very uniform and may include different crystal structures, such as co-existing crystal phases and/or lattice distortion. The way in which the lattice plane changes due to strain also might depend on the position in the sample, and the average information might have some limits. Therefore, it is important to analyse the sample with good lateral spatial resolution in real space. Although various techniques for diffraction topography have been developed for single crystals, it has not always been easy to image polycrystalline materials. Since the late 1990s, imaging technology for fluorescent X-rays and X-ray absorption fine structure has been developed via a method that does not scan either a sample or an X-ray beam. X-ray diffraction imaging can be performed when this technique is applied to a synchrotron radiation beamline with a variable wavelength. The present paper reports the application of X-ray diffraction imaging to bulk steel materials with varying hardness. In this study, the distribution of lattice distortion of hardness test blocks with different hardness was examined. Via this 2D visualization method, the grains of the crystals with low hardness are large enough to be observed by X-ray diffraction contrast in real space. The change of the d value in the vicinity of the Vickers mark has also been quantitatively evaluated.

Ultrafast spectroscopy reveals singlet fission, ionization and excimer formation in perylene film

Singlet exciton fission (SF) is a spin-allowed process whereby two triplet excitons are created from one singlet exciton. This phenomenon can offset UV photon energy losses and enhance the overall efficiency in photovoltaic devices. For this purpose, it requires photostable commercially available SF materials. Excited state dynamics in pure perylene film, ease of commercial production, is studied by time-resolved fluorescence and femtosecond transient absorption techniques under different photoexcitation energies. In film, polycrystalline regions contain perylene in H-type aggregate form. SF takes place from higher excited states of these aggregates in ultrafast time scale < 30 fs, reaching a triplet formation quantum yield of 108%. Moreover, at λex = 450 nm singlet fission was detected as a result of two-quantum absorption. Other competing relaxation channels are excimer (1 ps) and dimer radical cation formation (< 30 fs). Excimer radiatively relaxes within 19 ns and radical cation recombines in 3.2 ns. Besides, exciton self-trapping by crystal lattice distortions occurs within hundreds of picosecond. Our results highlight potential of simple-fabricated perylene films with similar properties as high-cost single crystal in SF based photovoltaic applications.

Deformation Effect on Microtwinning and Crystal Lattice Distortion of Polycrystalline Cu–Al Alloys

The paper considers the dynamics of changing of misoriented dislocation substructures appearing at a stage of developed plastic deformation. The types of defects, which induce the distortion of the crystal lattice are studied in detail. The quantitative parameters are obtained for the lattice distortion in alloys at a different grain size. It is found that the lattice bending and torsion parameters in the misoriented cellular-network and microtwin substructures depend on the degree of deformation. The lattice distortion is investigated both in the vicinity and far from the microtwins. It is shown that the microtwin formation occurs with increasing deformation at a different grain size.

Effect of Glow Discharge Treatment on the Depth and Degree of Structural Phase Modification of Tool Steel Products

The structure and phase composition of 1.1625, 1.2080 and 1.3343 tool steels (DIN) were studied and the research results are presented. The glow discharge treatment is shown to lead to dissolution and redistribution of the carbide phase, a change in the degree of crystal lattice distortion of the matrix phase, and a decrease in the residual austenite in the surface layer to a depth of 80 μm, which results in a 15% to 30% increase in the microhardness of the surface layers of materials.

Energy Band Gap Modeling of Doped Bismuth Ferrite Multifunctional Material Using Gravitational Search Algorithm Optimized Support Vector Regression

Bismuth ferrite (BiFeO3) is a promising multiferroic and multifunctional inorganic chemical compound with many fascinating application potentials in sensors, photo-catalysis, optical devices, spintronics, and information storage, among others. This class of material has special advantages in the photocatalytic field due to its narrow energy band gap as well as the possibility of the internal polarization suppression of the electron-hole recombination rate. However, the narrow light absorption range, which results in a low degradation efficiency, limits the practical application of the compound. Experimental chemical doping through which the energy band gap of bismuth ferrite compound is tailored to the desired value suitable for a particular application is frequently accompanied by the lattice distortion of the rhombohedral crystal structure. The energy band gap of doped bismuth ferrite is modeled in this contribution through the fusion of a support vector regression (SVR) algorithm with a gravitational search algorithm (GSA) using crystal lattice distortion as a predictor. The proposed hybrid gravitational search based support vector regression HGS-SVR model was evaluated by its mean squared error (MSE), correlation coefficient (CC), and root mean square error (RMSE). The proposed HGS-SVR has an estimation capacity with an up to 98.06% accuracy, as obtained from the correlation coefficient on the testing dataset. The proposed hybrid model has a low MSE and RMSE of 0.0092 ev and 0.0958 ev, respectively. The hybridized algorithm further models the impact of several doping materials on the energy band gap of bismuth ferrite, and the predicted energy gaps are in excellent agreement with the measured values. The precision and robustness exhibited by the developed model substantiate its significance in predicting the energy band gap of doped bismuth ferrite at a relatively low cost while the experimental stress is circumvented.

Study of the K2Ti6-xZrxO13 (x = 0 - 1) solid solution for enhancing the photocatalytic hydrogen production: Oxygen vacancies playing an important role in the catalytic performance

The K2Ti6-xZrxO13 (x = 0–1) solid solution was prepared by the traditional solid-state synthesis method. The X-Ray diffraction patterns presented a proportional increase in the cell volume and crystal lattice distortion according to the increment of the Zr4+ species concentration in the reactant mixture. The morphological characterization showed a decrease in particle size average as a result of the zirconium presence due to crystal distortion. The photocatalytic performance was evaluated in the hydrogen evolution reaction in the presence of methanol. In this context, the K2Ti5ZrO13 solid solution exhibited the highest performance (72 μmolg−1 h−1) due to the higher presence of defects such as oxygen vacancies because of the Zr incorporation into the crystalline structure. In this context, these anionic defects can act as electron traps in bulk material and reduce recombination of charges; meanwhile, oxygen vacancies in surface create reactive Ti3+ ions, where the reactions of interest take place.

Vacancies Substitution Tuning Photoluminescence and Distortion Triggered Eu Migration in NASICON-Type Phosphors

Phosphor-converted white light-emitting diodes (PC-WLEDs) are an energy-saving alternative to traditional light sources, for which efficient and thermal stable phosphors are in high demand. Here, the NASICON-type Na₃₊ₓ□₁–ₓSc₂–ₓMgₓ(PO₄)₃:Eu²⁺ (N□SMₓPO:Eu²⁺) phosphor is synthesized for Na vacancies repair. The photoluminescence quantum yield (PLQY) and the emission morphology of solid solution are dramatically affected by the composition, with the PLQY improving by 27% and the emission spectra red-shifting by 11 nm going from x = 0.0 to x = 0.3. These highlights likely stem from the enhanced structural rigidity and the distortion of NaO₆₍₈₎ polyhedra, respectively. Temperature-dependent emission spectra reveal the thermal stable luminescence of the series. A luminescence intensity of ≥90% relative to the room-temperature value is observed at 425 K. The LED device with the blending of N□SM₀.₃PO:Eu²⁺ and commercial components generates CRI (color-rending indices) = 88 and CCT (correlated color temperatures) = 5209 K, characteristic of high-quality white light. More interestingly, the distortion of crystal lattice could switch to the migration of Eu ion to (Sc/Mg) site at x = 0.4. The phenomenon leads to the oxidation of Eu²⁺, optically rapidly weakening the photoluminescence. Modifying the lattice distortion in some type phosphors may be a very useful approach to improve the efficiency of luminescence materials.

SnO2 nanoparticle reformed their magnetic properties by the efficiency of dopant cobalt (Co) in (Tin) Sn sites

Cobalt doped SnO2 nanoparticles were prepared for different molar concentration 2%, 4% & 6% of Co by Chemical co precipitation method. The prepared samples were characterized by X-ray diffraction (XRD), Scanning electron Microscopy (SEM) and Vibrating sample magnetometer for their Structural, Magnetic Properties. The doping concentration of Co induces crystal phase, crystallite size, lattice distortion, optical and magnetic properties were investigated. XRD Results showed that Co2+ replaces Sn4+ in the crystal lattice of SnO2, which enhanced the growth of crystallite size and suppressed the transformation from anatase to rutile phase due to lattice distortion produced in SnO2. An efficient method for inducing the ferromagnetic behavior from increasing the Co concentration from 2 to 6% was known from the magnetization versus magnetic field (M−H) curves at room temperature of the Co doped SnO2 samples. The dominant magnetic interaction between Co ions, and hence, the ferromagnetic behaviour increases for increase in Co2+ doping concentration. Consequently, to achieve the good ferromagnetic character in these materials, the concentration of Co dopant has to be properly optimized.