Degree Of Lattice Distortion Research Articles

A Review of Ab Initio Calculation on Lattice Distortion in High-Entropy Alloys

Lattice distortion is one of the four core effects responsible for the unprecedented mechanical behaviors of high-entropy alloys (HEAs). Lattice distortion in HEAs has been investigated in experiments and estimated in theory. In this review, we focus on the lattice distortion based on available ab initio calculations. The degree of lattice distortion and its influence on the ground-state property, local magnetic moments, phase stability, and mechanical performance are reviewed in single-phase high-entropy alloys.

Influence of Ag on TCR and MR of La0.7(Ca0.27Sr0.03)MnO3:Ag0.2 ceramics subjected to cross magnetic fields

Abstract In this account, polycrystalline La0.7(Ca0.27Sr0.03)MnO3:Ag0.2 (LCSMO:Ag) ceramics were synthesized by the sol-gel method followed by solid-state doping. The Ag amounts doped into grain boundary and cell lattice could be adjusted by changing the sintering temperature from 1000 °C to 1500 °C. The temperature coefficient of resistivity (TCR) and magnetoresistance (MR) of the obtained LCSMO:Ag ceramics were tested under cross magnetic field with directions parallel and perpendicular to the flat of bulk. The difference between TCR and MR values reached their maxima at sintering temperature of 1450 °C, meaning that degree of lattice distortion reached maximum value. The combined data from X-ray diffraction (XRD) and scanning electron microscopy (SEM) demonstrated that Ag was doped into the grain boundary and lattice cell, and Ag played an important role during the process. The influence of Ag-doping on TCR and MR suggested that degree of lattice distortion can be adjusted by doping, leading to change in isotropic ceramics into anisotropic ceramics without damage. Application of parallel magnetic fields shifted the application temperature to room temperature, and response sensitivity of the ceramics to magnetic field further increased. Overall, these findings look promising for future applications in photoelectric and magnetic devices.

Research on ground surface characteristics of prism-plane sapphire under the orthogonal grinding direction

Abstract As a typical single crystal material, the ground surface characteristics of sapphire are influenced by the relationship between machining direction and crystalline orientation. In this paper, the effects of grinding direction on the surface characteristics of the prism-plane sapphire were investigated by a series of sapphire grinding experiments under the orthogonal machining directions. The ground surface topography, surface layer lattice residual stress and degree of lattice distortion were measured. The results show that the grinding force with the grinding direction along the c-axis is greater than the grinding force along the m-axis or the a-axis, and serious damage was generated to the ground surface with grinding direction along the c-axis. The full width at half maximum intensity value of the X-ray rocking curve indicates that the residual stress of the ground surface with machining direction along the c-axis is greater than that along the m-axis or the a-axis, and the molten KOH etching analysis results manifest that the degree of lattice distortion of the ground surface with machining direction along the c-axis is higher than that along the m-axis or the a-axis. Therefore, the grinding direction along the m-axis or the a-axis is better suited to process prism sapphire.

Phase separation mechanism and property changes in In–41Sn–9Zn under the current stressing

Phase separation mechanism and property changes in In–41Sn–9Zn solder was investigated with the current density of direct current 1.0 × 103 A/cm2. The results indicated that the phase separation was affected by the combination of electron wind force and back stress. The different degree of lattice distortion between different regions was one of the causes of the back stress. In the alloy, In-rich β phases and Sn-rich γ phases were segregated at the cathode side and anode side respectively, while Zn atoms didn’t migrate to the two poles significantly. Sn was the main diffusing atom $$\left( {\left| {{\text{Z}}_{\text{Sn}}^{*} } \right| > \,\left| {{\text{Z}}_{\text{In}}^{*} } \right|} \right)$$ in the alloy, so the volume change rates at the anode side was about four times higher than that of the cathode side. After 72 h electromigration, the cathode–anode difference in micro-hardness, melting point, thermal enthalpy and melting interval was about 0.3 Mpa, 2 °C, 4.18 J/g, and 0.9 °C, respectively.

Enhanced CH4 and CO Oxidation over Ce1- xFe xO2-δ Hybrid Catalysts by Tuning the Lattice Distortion and the State of Surface Iron Species.

CeO2-Fe2O3 mixed oxides are very attractive as catalysts for catalytic oxidation. Herein, we report the structural dependence of the Ce1- xFe xO2-δ catalysts for CH4 combustion and CO oxidation via changing lattice distortion degrees, surface Fe2O3 states, and oxygen vacancy concentrations. The lattice distortion degree and oxygen vacancy concentration of Ce-Fe-O solid solution can be tuned by changing the contents of Fe and the precipitation temperatures in the preparation process. The precipitation at relatively high temperature (70 °C) promotes the lattice distortion, whereas a lower temperature (0 °C) helps the formation of surface oxygen vacancies. The in situ diffuse reflectance infrared/Raman experiments and the physicochemical characterization suggest that both the CO and CH4 oxidations mainly follow a Mars-van Krevelen mechanism. Both the lattice distortion and the surface iron species play a crucial role in determining the catalytic activity by affecting the redox property of the catalysts. The surface iron species, combined with the oxygen vacancies, improve the catalytic performance by enhancing the adsorption capacity of reactants and reducibility of catalysts. The lattice distortion of CeO2 contributes to the catalytic activity by tuning the oxygen mobility in the bulk, which promotes the re-oxidation rate of catalysts.

Density-functional theory study of the body-centered-cubic and cI16 hard-sphere crystals.

The properties of the body-centered-cubic (bcc) solid phase of hard spheres are challenging to compute because of its lack of mechanical and thermodynamic stability, yet this structure remains of interest for theoretical and practical reasons. Density-functional theory (DFT) studies of the bcc hard-sphere solid, using the most accurate functionals from fundamental measure theory, have yielded results with unphysical behaviors in structural and thermodynamic properties. We recently reported [Warshavsky et al., J. Chem. Phys. 148, 024502 (2018)] a Monte Carlo (MC) simulation study of hard spheres initiated in a bcc structure. We observed that such systems, even under constant-volume and single-occupancy-cell constraints, rapidly evolved into either a crystalline state with the cI16 structure or one of a few amorphous states. With these observations in mind, we revisited the DFT calculations of the bcc hard-sphere system by allowing for a bcc-to-cI16 structural transformation. Specifically, the free energy functional was minimized with respect to a density profile having two scalar parameters: the traditional alpha parameter characterizing the width of the Gaussian density distribution around each lattice site and a geometric parameter characterizing the bcc-to-cI16 structural transition. The numerical solutions were physically reasonable across the entire density range. At all densities above ρbσ3 = 1.0, a cI16 structure had lower free energy than the corresponding perfect bcc structure. The degree of lattice distortion from bcc to cI16 increased with density up to the close-packing limit. Finally, the predicted values of the structural and thermodynamic properties were in excellent agreement with those extracted from our previous MC simulations.

Thermal Conductivity and Mechanical Properties of As-Cast and As-Extruded Mg-Zn-Mn Alloys

As-cast and as-extruded Mg-[x]Zn-0.3Mn (x=1.5, 2.0 wt.%) alloys were prepared by means of medium-frequency induction-heating technique and extrusion process, respectively. The microstructural characteristics, thermal conductivity and mechanical properties of the samples were characterized. The research results show that the samples are composed of major α-Mg and minor second phases MgZn2. For the as-extruded samples, the grain size is refined. After extrusion, much more second phases were precipitated from α-Mg matrix and the dislocations were reduced. The degree of lattice distortion was decreased for as-extruded samples. Because of the decline of lattice distortion degree, the as-extruded samples display much higher thermal conductivity than the as-cast samples. Additionally, on account of lower lattice distortion, Mg-1.5Zn-0.3Mn alloy has a bit larger thermal conductivity than Mg-2Zn-0.3Mn alloy. Finally, the as-extruded alloys present good mechanical properties based on the fine-grained strengthening and second-phase strengthening mechanism.

Effect of mechanical activation on the leaching kinetics of niobium-bearing mineralisation in KOH hydrothermal system

The leaching kinetics of niobium-bearing mineralisation in KOH hydrothermal system was investigated. Particle size analyzer, XRD and SEM were used for studying the influences of mechanical activation on particle size, surface area, crystal structure and surface morphology of niobium-bearing mineralisation. The results showed that mechanical activation decreased the mineral particle size, increased the surface area and the degree of lattice distortion or disorder. Kinetics of alkali leaching of niobium is modeled and explained. The activation energy of niobium leaching from unactivated niobium-bearing mineralisation was 45.6 kJ/mol. When the mineralisation was activated for 10 min and 30 min, the activation energy decreased to 32.2 kJ/mol and 21.9 kJ/mol respectively. Compared with the non-mechanical activation method, mechanical activation greatly improved the activity of niobium-bearing mineralisation and decreased the activation energy, so that the reaction speed was accelerated remarkably.

Study of materials structure physics of isomorphic LiNbO3 and LiTaO3 ferroelectrics by synchrotron radiation X-ray diffraction

Electron charge density studies of stoichiometric LiNbO3 and LiTaO3 ferroelectrics have been carried out by analyzing the synchrotron radiation X-ray powder diffraction data using a combination of the Rietveld and maximum entropy methods. The clear relationships between the Nb(Ta)–O bond length, the electron charge density on the Nb(Ta)–O bond, and the phase transition temperature TC are revealed for isomorphic structures. Nb(Ta)–O bonding plays an important role in the elevation of TC. The TC in LiNbO3 being higher than that in LiTaO3 is attributed to the larger lattice distortion of the Nb–O oxygen octahedron in LiNbO3. The validity of estimating TC for LiNbO3 family crystals from the degree of lattice distortion in the ferroelectric structure is discussed.

Transformation pathways and isothermal compressibility of a MTN-type clathrasil using penetrating and non-penetrating fluids

The high-pressure behavior of the natural MTN-type clathrasil chibaite was investigated with in situ single-crystal X-ray diffraction and Raman spectroscopy under hydrostatic pressures up to 10.3 GPa. The experiments were conducted in diamond-anvil cells using 4:1 methanol-ethanol mixture (ME), helium (He) and neon (Ne) as pressure-transmitting media. The pressure dependent unit-cell volumes of the room-pressure polymorph yield an isothermal bulk modulus KT0 = 25.75 (19) GPa for the compression in the non-penetrating ME fluid. Due to the penetration of the Ne and He atoms into the cages of the framework, the crystal structure is significantly stiffened resulting in KT0 = 42.5 (1.2) GPa (Ne) and KT0 = 58 (2) GPa (He). Under the influence of pressure both the evolution of the Raman spectra and the change in cell metrics indicate a distortion of the lattice without leading to a complete pressure-induced amorphization, as observed for many comparable porous structures. Compressed in the non-penetrating ME, the cubic Fd3¯m framework of chibaite undergoes a first transformation step in the pressure range between 1.7 GPa and 2.2 GPa and a second one between 3.9 GPa and 4.3 GPa. The accompanied formation of crystal domains did not allow a reliable determination of the distorted crystal structures. The unit-cell parameters might suggest a monoclinic metric for pressures >1.7 GPa and a monoclinic or tetragonal metric for pressures >3.9 GPa. However, in some samples even the co-existence of crystal domains of a different degree of lattice distortions has been proved.

Ni-V(or Cr) Co-addition Cu alloy films with high stability and low resistivity

In order to inhibit Cu, interconnecting in ultra-large-scale integration, from diffusing with surrounding dielectric materials and enhance its chemical inertness and maintain its excellent electrical performance as well. In this paper, the stable solid solution cluster-plus-glue-atom model was used to design the composition of Cu seed layers. In this model, insoluble element V (or Cr) was dissolved in Cu via Ni which is soluble both with Cu and V(or Cr), causing a certain degree of lattice distortion to improve the stability of Cu film. Cu-Ni-V(or Cr) alloy films were deposited directly on single crystal Si(100) substrates, without a designated barrier layer, subsequently annealed in vacuum. For the (V0.8/12.8Ni12/12.8)0.5Cu99.5 (at.%) film with the addition of large atomic radius element V, it showed the minimum electrical resistivity of 3.2 μΩ·cm after 500 °C/1 h annealing; after 500 °C/40 h annealing, no diffusion between Cu and Si was observed and the resistivity remained stable. Likewise, the (Cr1.4/13.4Ni12/13.4)0.4Cu99.6 film also remained a minimum resistivity of 3.0 μΩ·cm after annealing at 500 °C for 40 h. The greater the relative lattice distortion is in a single system, the higher the stability and the lower resistivity achieved. Obviously, the stability of Cu alloy film which satisfy the requirements of the microelectronics industry can be improved dramatically by the additive of Ni and V (or Cr) conform to the proportion of clusters.

Bond length pattern associated with charge carriers in armchair graphene nanoribbons.

The geometry configuration of charged armchair graphene nanoribbons (AGNRs) is theoretically investigated in the framework of a two-dimensional tight-binding model that includes lattice relaxation. Our findings show that the charge distribution and, consequently, the bond length pattern is dependent on the parity of the nanoribbon width. In this sense, the lattice distortions decrease smoothly for increasingly wider GNRs. As should be expected, AGNRs belonging to a particular family present similar patterns for the bond lengths. The interplay between the electron-phonon coupling and band gap is also investigated. The results show that the electron-phonon coupling strength is fundamental to promote the transition from metallic towards semiconducting-like behavior for the band gap. Most important, such strength is crucial on defining the degree of lattice distortions in AGNRs.

The mechanism of an increase in electrical resistance in Al thin film induced by current stressing

A 10mm×2mm×500nm Al thin film was stressed with electric current at 1.5–3.0×105Acm−2 for 1h under an ambient atmosphere. Ex situ variations in the sheet resistance induced by current stressing were measured with a four-point probe. The critical current density for the resistance change was observed between 1.5×105 and 2.0×105Acm−2. The electrical resistance reached a maximum increment of 5.47% at 2.5×105Acm−2. The lattice structure of the Al thin film was investigated with a high resolution transmission electron microscope to determine the fundamental effects of electric current stressing on the electrical property of the metal film. The high resolution lattice images incorporating a selected area fast Fourier transform indicated a large degree of lattice distortion and high dislocation density, up to 8.60×1016m−2, in the metal film after current stressing at 3.0×105Acm−2. The dislocations are believed to have been generated by the impingement of electron wind. In situ synchrotron X-ray diffraction further evidenced a high degree of lattice strain, as great as 1.1% at 3.0×105Acm−2, as estimated from the low angle shifts in the diffraction peaks. The generation of dislocations and the lattice strain induced by current stressing were orientation-dependent, as determined by the d-spacing of the lattice orientation. The formation of a high dislocation density and the subsequent buildup of lattice strain caused to an increase in electrical resistance of the Al thin film.

Nanostructure evolution and surface modification of tungsten exposed to low energy, high flux deuterium plasma

One of the most important changes of plasma-facing material is plasma-induced damage which limits the material lifetime in fusion reactors. In this study, the influence of exposure conditions on tungsten nanostructure formation and surface modification was investigated. TEM specimens and bulk samples were prepared and exposed to deuterium plasmas with different fluxes (4.0–10.0×1021Dm−2s−1), fluences (2.5–10.0×1025Dm−2) and temperatures (343–513K), while ion energy was constant (60eV). Distortion, nano-polycrystalline and amorphous structure were observed as irradiation damage. Increasing exposure intensity results in severer damage: (1) amorphous structure arises with increasing temperature; (2) deformation region greatly extends at a higher fluence; (3) degree of lattice distortion increases in high flux. Furthermore, surface morphology featured by blisters changes dramatically as well. Nanostructures and surface morphology observation indicates that nanostructure evolution is strongly related to surface modification, and it would influence the properties of tungsten.

Microstructure and impedance properties of La, Ce multi-rare earth ions doped Na0.5Bi2.5Nb2O9 Aurivillius type ceramics

(Li, Ce, La) multi-doped Na0.5Bi2.5Nb2O9 ceramics were prepared by a conventional solid state sintering method. Microstructure of sintered ceramics was examined by the X-ray diffraction and scanning electron microscopy. The introduction of voluminous La3+ cations decreases the degree of lattice distortion, leading a lower Curie-temperature. The detailed electrical conduction behaviors were determined by the electrochemical impedance spectra (EIS). The electrical properties were investigated as a function of frequency (102–106 Hz) at various temperatures (350–750 °C). The underlying physical mechanism of electrical properties at high temperature for multi-rare-earth doping NBN-based was studied via an assistance of EIS techniques. There were a set of Debye-like relaxation peaks in the imaginary part of impedance and electric modulus data. Oxygen vacancies are responsible for both ac conduction and dielectric relaxation processes. A discontinuous variation of the exponent parameter n is found owing to a ferroelectric-ferroelastic phase transition around 550 °C.

Carbonado revisited: Insights from neutron diffraction, high resolution orientation mapping and numerical simulations

One of the most controversial diamond types is carbonado, as its origin and geological history are still under debate. Here, we investigate selected carbonado samples using neutron diffraction and high resolution orientation mapping in combination with numerical simulations. Neutron diffraction analyses show that fine grained carbonado samples exhibit a distinct lack of crystallographic preferred orientation. Quantitative crystallographic orientation analyses performed on transmission electron microscope (TEM) sections reveal that the 2–10μm grains exhibit locally significant internal deformation. Such features are consistent with crystal plastic deformation of a grain aggregate that initially formed by rapid nucleation, characterized by a high number of nucleation sites and no crystallographic preferred orientation. Crystal plastic deformation resulted in high stress heterogeneities close to grain boundaries, even at low bulk strains, inducing a high degree of lattice distortion without significant grain size reduction and the development of a crystallographic preferred orientation. Observed differences in the character of the grain boundary network and internal deformation structures can be explained by significant post-deformation annealing occurring to variable degrees in the carbonado samples. Differences in intensity of crystal bending and subgrain boundary sharpness can be explained by dislocation annihilation and rearrangement, respectively. During annealing grain energy is reduced resulting in distinct changes to the grain boundary geometry. Grain scale numerical modelling shows that anisotropic grain growth, where grain boundary energy is determined by the orientation of a boundary segment relative to the crystallographic orientation of adjacent grains results in straight boundary segments with abrupt changes in orientation even if the boundary is occurring between two triple junctions forming a “zigzag” pattern. In addition, in diamond anisotropic grain growth results in triple junctions that rarely show 120° angles.Our results support the interpretation that carbonados may have undergone at least 2 or 3 stages of development with rapid nucleation, crystal plastic deformation to low strains and variable degrees of post-deformation annealing. Such a history is commonly observed in Earth's crustal or mantle rocks. Hence, for carbonados it is not necessary to invoke an extraordinary and/or extraterrestrial origin and history.The combination of methods utilized here, promises to help advance our understanding of diamond and diamond aggregates in the future.

Anomalous behavior of the dielectric response of quantum paraelectric CaTiO3 with iron impurities

We report on the studies of lattice dynamics and crystal structure of natural perovskite with the general formula CaTiO3:0.01Fe by dielectric spectroscopy and X-ray diffraction in a wide temperature range. In contrast to the “chemically pure” synthetic perovskite, the lattice dynamics of the Fe-containing natural sample exhibits a structural instability in the vicinity of 240 K. Our studies of the behavior of magnetic moment of CaTiO3:0.01Fe demonstrate that in the temperature region from 4.3 to 300 K this material is paramagnetic. No changes in the crystal symmetry have been observed in the structural studies, which can be explained by the small degree of lattice distortions, as has been observed previously for isotopically substituted SrTiO318. Conductivity measurements and analysis of the dielectric response dispersion of CaTiO3:0.01Fe have shown that the dispersion is due to the Maxwell–Wagner mechanism and can be attributed to oxygen vacancies present in the mineral.

Four organo-templated structures with DFT-zeotype topology: Variation in symmetry of similar microporous structures

Four novel microporous compounds H2(C2H8N2)(ZnAsO4)2 (1), H2(C2H8N2)(Co0.1Zn0.9AsO4)2 (2), H1.8(C2H8N2)(Fe0.1Zn0.9AsO4)2 (3) and H2(C2H8N2)(ZnPO4)2 (4) containing ethylenediammonium cation, H2(C2H8N2)2+ (H2en2+), and ethylenediamine molecule, C2H8N2 (en), have been hydrothermally synthesized. While 1–3 exhibit twinned DFT-zeotype structure and crystallize in P42/n, 4 is characterized by the appearance of new orthorhombic space group Pcca, previously not observed among the known DFT-zeotype compounds. The symmetry relationships analyses revealed the extended Bärnighausen tree. The main feature of the cobalt blue and reddish brown compounds 2 and 3 is their novel chemical composition which was confirmed by SEM/EDX analysis. In the structure of 1, H-atoms positions, previously not reported, were calculated and refined to reasonable positions using riding model.The DFT anionic frameworks of 1–4 are characterized by 4M, 6M and 8M tetrahedral rings, which produce three mutually perpendicular 8M ring channels. At the intersections of these channels H2en2+ cations are accommodated and hydrogen-bonded to the adjacent oxygen atoms of the framework. Only in 3, H2en2+ is partly substituted by electroneutral en to maintain charge compensation. The single-crystal Raman spectra and Fourier transform infrared (FTIR) absorption spectra were interpreted on the basis of characteristic vibrations of AsO4 and PO4 groups, as well as of NH3, NH2 and CH2 groups from the H2en2+ cation or en molecule.The results of lattice distortion and similarity analyses showed that the DFT-zeotype structures, which incorporate larger tetrahedral cations, have a higher degree of lattice distortion and are less similar to the ideal structural models derived from the aristotype.

Single crystal growth, x-ray structure analysis, optical band gap, raman spectra, strain tensor and photoluminscence properties in [HgCl<sub>4</sub>]<sup>-</sup> [R]<sup>+</sup> and [ZnCl<sub>4</sub>]- [R]+ (R= 2-amino-5- chloropyridine) hybrid materials

The single crystal growth of tetrachloromercurate (II) [HM-1] and tetrachlorozincate (II) [HM-2] with 2-amino-5-chloropyridine has been performed by slow cooling (SC) crystal growth technique of solution growth methodin which needle shaped transparent single crystals (0.5 x 0.2 x 0.2)mm were obtained. The crystal structures of these hybrid materials have been studied by X-ray diffraction, experimental and computational methods. [HgCl 4 ] 2- anions have a distorted tetrahedral geometry and the tetrahedra hybrid structure exhibit interwoven inorganic-organic layers mingled through N-H δ+ ...Cl δ- hydrogen bonding interactions. The mercurophilic interactions [Hg...Hg = 3.984(5)A] and halogen interactions [Cl...Cl = 3.406(2)A] form 2D parallelogram pattern of secondary interactions in [HM-1] whereas for [HM-2] crystal structure is stabilized by Cl...Cl = 3.357(2)A interactions. UV-vis absorption spectra depict the change in optical band gap from 3.01 eV to 3.42 eV on replacing the metal halide group, could be due to increase in optical absorption as a function of wavelength. The Raman and Hyper-Raman tensors calculations were performed based on single crystal X-ray data and the Lagrangian strain tensor calculations show the degree of lattice distortion = 1.794 between [HM-1] and [HM-2] which are useful tools for the optical response properties of inorganic-organic hybrid derivatives. The photoluminescence emission spectra peaks were observed in the wavelength range of 371 to 598 nm for material [HM-1] and in the wavelength range of 384 to 600 nm for material [HM-2] and lie in the visible range for both materials.

Effects of atomic scale imperfection at the interfaces of CoSi2and Si (100) on Schottky barrier contacts

We report here the correlation of electrical properties on Schottky barrier contacts and atomic scale imperfections based on the degree of lattice distortion and moire fringes at the interfaces of CoSi2 and Si. The I-V measurements showed that the higher levels of perfection of the interfaces gave better Schottky barrier characteristics and we discuss the implications of the transport property at Schottky barrier contacts.