Deformation Of Crystal Structure Research Articles

Low-temperature investigation of natural iron-rich oxoborates vonsenite and hulsite: thermal deformations of crystal structure, strong negative thermal expansion and cascades of magnetic transitions

This work is devoted to an investigation of the magnetic properties and thermal behaviour of the natural oxoborates vonsenite and hulsite in the temperature range 5–500 K. The local environment, the oxidation states of the Fe and Sn atoms, and the charge distribution were determined using Mössbauer spectroscopy and are in accordance with a refinement of the crystal structure of hulsite from single-crystal X-ray diffraction data (SCXRD) in anisotropic approximation for the first time. The magnetic properties were studied by vibrating sample magnetometry (VSM) (5 ≤ T ≤ 400 K) and are reported for the first time for iron-rich hulsite. Both oxoborates show a very complex magnetic behaviour. Cascades of magnetic transitions are revealed and the critical temperatures were determined. The sequences of magnetic transitions in both vonsenite and hulsite with increasing temperature were found to be as follows: magnetically ordered state → partial magnetic ordering → paramagnetic state. According to X-ray diffraction data (93 ≤ T ≤ 500 K), these processes are accompanied by anomalies in the unit-cell parameters and thermal expansion of the oxoborates at critical temperatures. A strong negative volume thermal expansion is observed for both oxoborates at temperatures below ∼120 K.

Exploring the coupling relationship between hydrocarbon generation of continental shale and nanopore structure evolution\u2014A case study of Shahejie formation in Bohai Bay Basin

The nano-scale pore structure of shale is closely related to the self-generated and self-accumulated shale oil and gas. The Bohai Bay Basin is a crucial oil-bearing basin in eastern China, and the Paleogene Shahejie Formation is the most important source rock section in this area. In order to study the internal relationship between hydrocarbon generation evolution and pore structure characteristics of source rocks, we conducted hydrocarbon generation simulation tests with a closed gold tube system, and heated up original rocks from Shahejie Formation in Laizhou Bay Sag, southern Bohai Bay Basin, from 290 °C to 440°C at different heating rates. Besides, we carried out low-temperature N2 adsorption experiments on sample residues, and measured their pore structure characteristic parameters. The results show that with the increase of simulated temperature, the specific surface area and pore volume of nano-pores below 10 nm (which are mainly organic pores) decrease first and then increase, while those of nano-pores above 10 nm increase all the way. The evolution trend of total specific surface area and pore volume is mainly controlled by pores below 10 nm which are mainly organic pores, especially micropores below 2 nm. There are two main factors affecting the development of inorganic pores: (1) Dissolution of organic acids produced by pyrolysis of organic matter in hydrocarbon-generation evolution; (2) Deformation of crystal structure of mineral components under the combined action of temperature and pressure. The experimental results at different heating rates demonstrate that rapid settlement under geological conditions is not conducive to the development of nano-pores, especially micro-pores composed of organic pores.

Monitoring of friction node surfaces in the context of their physico-chemical interactions with lubricating media of different surface activity

The article deals with tribochemical influence of the surface activity of biosynthetic oils on the operational efficiency and reliability of lubricated friction nodes under the critical conditions. It is proved that the oil surface activity is caused by the structure and properties of their molecules and interactions with steel surfaces. Evaluating criteria of oil tribochemical activity influence on the steel surface modification has been studied. The significant influence of biooils on the steel surface nanolayer phase transformations, friction and steel wearing is claimed. It has been established that the effect of the steel crystal structure deformation and strengthening its surface depends on activity of composition of lubricant. It is proved that biooils lead to improved friction and wear indicators of lubricated samples. X-structural analysis of the steel surfaces showed that during friction the austenite is destroyed and ferrite is formed. Penetration in the lubricated steel nanolayers shows increasing the ferrite and decreasing the austenite content, that cases reducing the deformation degree of metal crystals, which leads to the strengthening of its surface under the plasticized layer and to decreasing the level of friction and wear due to the formed intersurface servitotribopolymer film, which is stable under critical friction.

Relationship among the Crystal Structure, Texture, and Macroscopic Properties of Tetragonal (Pb,La)(Zr,Ti)O3 Ferroelectrics Investigated by In Situ High-Energy Synchrotron Diffraction.

In situ diffraction investigations have played an important role in experimentally revealing the mechanism of piezoelectric and ferroelectric properties. In this study, a pure tetragonal ferroelectric ceramic of La-doped PbZr0.5Ti0.5O3 (LaPZT50) was investigated to eliminate the complex influence of phase coexistence. The electric field evolutions of the crystal structure, domain switching, and lattice deformation of the tetragonal phase have been revealed by in situ high-energy synchrotron X-ray diffraction. We found that the crystal structure of LaPZT50 is quite stable, showing a negligible change in the Pb-O bond length, unit cell volume, and spontaneous polarization upon application of an in situ external electric field. Importantly, the maximum macroscopic polarization of tetragonal LaPZT50 is defined by the 111-oriented grains. As determined by the intensity difference, the switching of non-180° domains plays a more significant role in contributing to the macroscopic strain than lattice deformation. These results further imply that the phase coexistence around the morphotropic phase boundary facilitates domain wall motion in the tetragonal phase and improves the ferroelectric and piezoelectric properties.

Synthesis and crystal structure of Mo2Ni1-xCrxB2 hard materials

Boride-based cermets possess attractive mechanical properties and are promising candidates for hard materials. Mo2NiB2–Ni-based cermet, which is a boride-based cermet, exhibits high hardness and attractive transverse rupture strength (TRS) properties through the crystal structure deformation that is caused by Cr or V substitution of Ni in the Mo2NiB2 phase. In this study, the effects of Cr substitution on the crystal structure, mechanical properties, and consistency were investigated. Cr-substituted Mo2Ni1-xCrxB2 samples were synthesized via the powder metallurgy method. A first-principle calculation was also conducted to obtain the bulk modulus of the Cr-substituted Mo2Ni1-xCrxB2. With the increase of the Cr content x, the tetragonal-Mo2NiB2 phase appeared, while the orthorhombic Mo2NiB2 phase disappeared. In the x = 0.6 samples, the Mo2Ni0.4Cr0.6B2, tet-Mo2NiB2 phase was observed. According to the Rietveld analysis, substituted Cr atoms occupied the Ni and Mo sites in the tet-Mo2NiB2 structure. The Rockwell A-scale hardness (HRA) measurement was performed to investigate the effects of the Cr content on the mechanical properties. The HRA values increased with the Cr content, and the maximum HRA value was approximately 87.1 for the x = 0.6 sample. The bulk modulus was also affected by the Cr content x in Mo2Ni1-xCrxB2, and the maximum value was attained at x = 0.75.

Investigation of thermal behavior of mixed-valent iron borates vonsenite and hulsite containing [OM4]n+and [OM5]n+oxocentred polyhedra byin situhigh-temperature Mössbauer spectroscopy, X-ray diffraction and thermal analysis

The investigation of elemental composition, crystal structure and thermal behavior of vonsenite and hulsite from the Titovskoe boron deposit in Russia is reported. The structures of the borates are described in terms of cation-centered and oxocentred polyhedra. There are different sequences of double chains and layers consisting of oxocentred [OM4]n+ tetrahedra and [OM5]n+ tetragonal pyramids forming a framework. Elemental composition was determined by energy-dispersive X-ray spectroscopy (EDX). Oxidation states and coordination sites of iron and tin in the oxoborates are determined using Mössbauer spectroscopy and compared with EDX and X-ray diffraction data (XRD). According to results obtained from high-temperature Mössbauer spectroscopy, the Fe2+ to Fe3+ oxidation in vonsenite and hulsite occurs at approximately 500 and 600 K, respectively. According to the high-temperature XRD data, this process is accompanied by an assumed deformation of crystal structures and subsequent solid-phase decomposition to hematite and warwickite. It is seen as a monotonic decrease of volume thermal expansion coefficients with an increase in temperature. A partial magnetic ordering in hulsite is observed for the first time with Tc ≃ 383 K. Near this temperature, an unusual change of thermal expansion coefficients is revealed. Vonsenite starts to melt at 1571 K and hulsite melts at 1504 K. Eigenvalues of thermal expansion tensor are calculated for the oxoborates as well as anisotropy of the expansion is described in comparison with their crystal structures.

Transformation of electron density distribution induced by the cation point defects in uranium dioxide

The ab initio calculations on electronic structure of the large fragments of UO2 crystal lattice was performed using Molecular Dynamics and fully relativistic Discrete Variational method. The four types of clusters corresponding to stoichiometric crystal and to the crystals with isolated uranium vacancy and uranium interstitial impurity were considered. We investigated the transformation of valence and vacant bands and the nature of chemical bonding. The estimation of electron density redistribution among atoms of several coordination spheres around defects was performed. In contrast to previous ab initio and semi-empirical calculations, our model included the point symmetry of defects and the possibility of charge transfer between defects and all nearest and next nearest neighbors. We obtained that the deformation of crystal structure and the covalent interactions minimizes (or completely prevent) the electron density transfer between atoms in the vicinity of defects.

Photoinduced Defect and Surface Chemistry of Niobium Tellurium Oxides ANbTeO6 (A = K, Rb, Cs) with Defect-Pyrochlore Structure.

The niobium tellurium oxides ANbTeO6 with varying A cations (A = K, Rb, Cs) and defect-pyrochlore crystal structure were used to investigate the effect of A on crystal-structure deformation and defect-chemistry. We show that the light absorption of these compounds in visible light is due to defects and not the effect of a low band gap. Using the materials in photocatalytic hydrogen generation, the prevailing defects and the surface composition change significantly during photocatalytic hydrogen evolution.

Crystal field deformation by Ce3+ doping in spinel Mn-Cr ferrite

We investigated the doping of the spinel structure Mn-Cr ferrite with cations of the rare-earth Ce. The material was characterized by X-ray diffraction, Raman spectroscopy, high-resolution transmission electron microscopy and saturation magnetization. The magneto-impedance showed a step-like drop in impedance that ranges from 10% to 45% at the highest and lowest biased electric field, respectively. There was no crystal structure deformation detected in the diffraction patterns, but rather the deformation of the crystal field was seen in the Raman spectra. We can conclude that doping a large rare-earth cation in a closed packed spinel structure results more in a distortion in the crystal field of the material rather than in its crystal structure. This crystal field distortion results in non-symmetric splitting of the energy states of the doping cations in octahedral and tetrahedral sites, for which Raman scattering shift is very sensitive, and can be seen also in magneto-impedance measurements.

Effect of the Mechanical Alloying and Spark Plasma Sintering on Microstructure, Phase Composition and Chemical Elements Distribution of Nb-Si Based Composite

Synthesis of the Nb-Si in-situ composite was attempted by mechanical alloying of element powders in vario-planetary ball mill. The particles size distribution was measured by laser diffraction, microstructures were examined with scanning electronic microscope, and the phase constituent were analyzed by X-ray diffraction. The amorphization of the Si during mechanical alloying, large amount of deformation of Nb crystal structure, and after all – the formation of supersaturated solid solution of Nb was observed. To stabilize microstructure and phase composition, a spark plasma sintering was attempted. After SPS microstructure consist of three main phases – Nbss, Nb5Si3 and Nb3Si.

Strain building and correlation with grain nucleation during silicon growth

This work is dedicated to the grain structure formation in silicon ingots with a particular focus on the crystal structure strain building and its implication in new grain nucleation process. The implied mechanisms are investigated by advanced in situ X-ray imaging techniques during silicon directional solidification. It is shown that the grain structure formation is mainly driven by Σ3 <111> twin nucleation. Grain competition phenomena occurring during the growth process lead to the creation of higher order twin boundaries, localised strained areas and associated crystal structure deformation. On the one hand, it is demonstrated that local strain building can be directly related to the characteristics of the twin boundaries created during silicon growth due to grain competition. On the other hand, space restriction due to competition during growth can be at the origin of local strain building as well. Finally, the accumulation of all these factors generating strain is responsible for spontaneous new grain nucleation. When occurring, both grain nucleation and subsequent grain structure reorganisation contribute to lower the strain in the growing ingot. It is demonstrated as well that the local distribution of the strained areas created during silicon growth is retrieved after cooling down, from melting temperature to room temperature, on top of an additional larger scale deformation of the sample due to the cooling down only.

Radiation Defects in Beryllium Oxide under Irradiation with Ni12+ Heavy Ions

The paper presents the results of a study of the formation and evolution of radiation defects under the irradiation of nuclear materials based on beryllium oxide with the heavy ions Ni12+. The irradiation with 100-MeV Ni12+ ions was carried out on a DC-60 accelerator, and the irradiation fluence was 1013–1014 ion/cm2. It has been established that the crystal lattice parameter changed insignificantly at low irradiation fluences typical of the formation of single defects. An increase in the irradiation fluence led to a sharp change in the parameter value and a root-mean-square displacement of atoms from lattice sites due to an increase in the concentration of distortions in the structure. It has been found that the magnitude of the displacements of atoms from lattice sites exponentially changed due to the occurrence of defect overlap areas at a fluence (1014 ion/cm2) with the subsequent formation of a large number of migrating defects, which lead to crystal structure distortion and deformation, because of the rupture of chemical bonds in the structure.

The effect of irradiation with swift heavy ions on the structural and morphological properties of beryllium oxide ceramics

In this study the results of structural and morphological changes in Ni 12+ heavy ion irradiated BeO ceramics are presented. Irradiation was carried out on DC-60 heavy ion accelerator using Ni 12+ ions with an energy of 100 MeV with irradiation fluence of 10 13 -10 14 ions/cm 2 . It has been determined that change in magnitude of atom displacements from lattice sites is exponential, which is conditioned by defect overlap regions occurrence at fluence of 10 14 ions/cm 2 , followed by formation of a large number of migrating defects in structure, leading to crystal structure distortion and deformation due to chemical bonds rupture. In case of defect overlap areas generation, characteristic for irradiation fluences of 5 × 10 13 - 10 14 ions/cm 2 , amorphous inclusions formation of more than 5% was observed, that leads to thermal conductivity decrease by (15-20)%.

Crystallographic contributions to piezoelectric properties in PZT thin films

We report on the correlated investigation between macroscopic piezoelectric properties and the microscopic deformation of crystal structures of both epitaxial and polycrystalline Pb(Zr,Ti)O3 (PZT) thin films grown on MgO and Si substrates, respectively. We observed the reversible elongation and contraction of lattice parameter under an applied electric field using synchrotron X-ray diffraction. The effective piezoelectric coefficients were estimated from the relationship between electric field and field-induced strain, and compared with those characterized by the macroscopic cantilever method. The electric field dependences of the piezoelectric coefficients obtained from both characterization were in good agreement with each other. The results also revealed large and nonlinear piezoelectric properties for the polycrystalline PZT thin film. The comparative discussion in this study provides valuable insights of crystallographic contributions and opens the way to improve the piezoelectricity in thin-film based piezoelectric devices.

The effect of Ni12+ heavy ion irradiation on the optical and structural properties of BeO ceramics

The paper presents study results of structural and optical changes in heavy ion irradiated BeO ceramics. Irradiation was carried out on DC-60 heavy ion accelerator using Ni12+ ions with an energy of 100 MeV with irradiation fluence of 1013-1014 ions/cm2. It has been established that intensity decrease and shape change of OSL (Optically Stimulated Luminescence) curves for irradiated samples are caused by concentration increase of defects and amorphous inclusions, which affect ceramics reflectance. It has been determined that change in magnitude of atom displacements from lattice sites is exponential, which has great influence on crystal structure distortion and deformation in case of defect overlap regions formation at large irradiation fluences.

Oxidant peroxo-synthesized monoclinic BiVO4: Insights into the crystal structure deformation and the thermochromic properties

In this study, a simple and novel hydrothermal approach was developed for the controllable synthesis of monoclinic scheelite BiVO4 using V2O5, Bi(NO3)3 and H2O2 as the starting materials. Diverse morphologies of BiVO4 including rods and branches were obtained by adjusting the H2O2 addition. We characterized these samples using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, in situ UV–vis diffuse reflectance spectroscopy and Fourier transform infrared spectroscopy to investigate the effects of crystal structure deformation on their thermochromic behaviors. The results showed that the greater was the degree of structural distortion, the better was the thermochromic performance. As compared to rod-like morphology, the branch-like BiVO4 material exhibited better thermochromic properties owing to the greater distortion of crystal structure.

Systematic Theoretical Investigations for Crystal Structure Deformation in Group‐III Nitrides: A First‐Principles Study

The crystal structure deformation path depending on lattice parameters and its energy barrier in group‐III nitrides are investigated by using density‐functional theory calculations. The calculations demonstrate that the energy difference in cohesive energy along the crystal structure deformation path strongly depends on the ionicity of III‐nitrides. It is also found that the lattice parameter ratio c/a of AlN and InN with Hexagonal (Hex) structure is much smaller than that of BN. Moreover, the energy barrier for structural deformation from Hex to wurtzite structures in BN is much larger than that of the other group‐III nitrides. The difference in the energy barrier originates from both the repulsive interaction among bond charges and the attractive interaction among ionic charges. These results imply that the ionicity is crucial for determining the energy change along the crystal structure deformation path as well as the structural stability of group‐III nitrides.

Stress-Induced Cubic-to-Hexagonal Phase Transformation in Perovskite Nanothin Films.

The strong coupling between crystal structure and mechanical deformation can stabilize low-symmetry phases from high-symmetry phases or induce novel phase transformation in oxide thin films. Stress-induced structural phase transformation in oxide thin films has drawn more and more attention due to its significant influence on the functionalities of the materials. Here, we discovered experimentally a novel stress-induced cubic-to-hexagonal phase transformation in the perovskite nanothin films of barium titanate (BaTiO3) with a special thermomechanical treatment (TMT), where BaTiO3 nanothin films under various stresses are annealed at temperature of 575 °C. Both high-resolution transmission electron microscopy and Raman spectroscopy show a higher density of hexagonal phase in the perovskite thin film under higher tensile stress. Both X-ray photoelectron spectroscopy and electron energy loss spectroscopy does not detect any change in the valence state of Ti atoms, thereby excluding the mechanism of oxygen vacancy induced cubic-to-hexagonal (c-to-h) phase transformation. First-principles calculations show that the c-to-h phase transformation can be completed by lattice shear at elevated temperature, which is consistent with the experimental observation. The applied bending plus the residual tensile stress produces shear stress in the nanothin film. The thermal energy at the elevated temperature assists the shear stress to overcome the energy barriers during the c-to-h phase transformation. The stress-induced phase transformation in perovskite nanothin films with TMT provides materials scientists and engineers a novel approach to tailor nano/microstructures and properties of ferroelectric materials.

The RIKEN-RAL Muon Facility and the Application of Muons for Studies of Magnetic Properties of Nano-Materials

An overview of the RIKEN-RAL Muon Facility is reported. The RIKEN-RAL Muon Facility has been established at the Rutherford-Appleton Laboratory in the UK in 1992 and started to be in used for material science studies from 1994 by applying intense pulsed muon beams. More than 380 publications have been published in international journals and more than 100 domestic and international collaborations have been organized. As an example of those collaborative studies, a preliminary result of one recent experimental study on the magnetism in gold nano-cluster is reported. Additionally, a recent computational result on a local effect induced by an injected muon is reported in order to show how the presence of the muon leads to a local deformation of the crystal structure, thus changing the muon’s own position in finding the final stopping site self consistently.

Effect of PCA on Nanosized Ulexite Material Prepared by Mechanical Milling

Raw ulexite (U-3 mm) mineral used as a initial material was milled by using mechanical milling method, the milling time of which is from 0 to 8 h. Particle size, morphology, elemental and crystal structure measurements of the U-3 mm material and milled powder (U_3%, process control agent amount: 3%) were performed. In particle size analysis, minimum $$d_{50},d_{10}$$ and $$d_{\mathrm{min}}$$ values of U_3% powder have been found to be 5.921 $$\upmu \hbox {m}$$ , 641 nm and 240 nm, respectively. Therefore, it has been reached to submicron level in particle size for the U_3% powder. Besides, optimum milling time has been detected to be 0.5 h. In morphology analysis, the U_3% powder has been observed to be more homogeneous compared to the U-3 mm material. In the analysis of element, the U_3% powder has been determined not to be a pure compound ( $$\hbox {Na}_{2}\hbox {O}{\cdot }2\hbox {CaO}{\cdot } 5\hbox {B}_{2}\hbox {O}_{3}{\cdot } 16\hbox {H}_{2}\hbox {O}$$ ). In crystal structure analysis, crystalline size of the U_3% powder has reduced to 10.3 nm at the end of 8 h. Moreover, crystal structure deformation caused by milling process of the U-3 mm material has improved thanks to PCA. The findings obtained from this work will be beneficial for nanoworks and industrial applications, e.g., civil engineering-pavement engineering materials, of ulexite (boron mineral) material.