Parent Crystal Research Articles

EBSD analysis of rhombohedral twinning in hematite crystals of naturally deformed iron formations

The rhombohedral twinning in hematite has an important role in the accommodation of the deformation of hematite single crystals and hematite aggregates. It is a contact twinning and occurs as lamellae parallel to the \{10{\overline 1}2\} planes of hematite as a result of twin gliding on such planes. On account of the recent applications of electron backscatter diffraction (EBSD) techniques in a wide range of microstructural studies, the determination of symmetry operations that relate crystals in a deformed crystalline aggregate is crucial for the full textural characterization. This study presents an EBSD-based crystallographic analysis of the rhombohedral twinning on hematite crystals of a naturally deformed banded iron formation. Manipulations of theoretical pole figures depicting the symmetry relation of the rhombohedral twinning and misorientation and crystallographic data obtained by EBSD are used to establish the rotational relationship between twin and parent crystals. A method for determining pairs of axes and angles of rotation was developed which can be extended to any other twin laws or misorientation patterns in any other crystal system. It was found that the hematite rhombohedral twins are related to the parent crystal by an approximately 85° rotation about the 〈02{\overline 2}1〉 directions. Hence it could be determined that this consists of a macroscopic twinning element which is an alternative to the conventional ones used to describe the symmetry of the twin. It also matches microscopic twinning elements for the rhomb twinning law. Additionally, this method allows the determination of the crystallographic orientation of the twin lamellae and which particular 〈02{\overline 2}1〉 axis satisfies the 85°〈02{\overline 2}1〉 pair of rotation. The use of an unambiguous angle–axis pair of rotation allows the identification of twin boundaries in complex and finely grained aggregates and the distinction of twinning laws in a particular crystal.

Twin Laws and Energy in Monoclinic Hydroxyapatite, Ca5(PO4)3(OH)

The most frequent twin law of the monoclinic hydroxyapatite crystal (HAp, S.G.: P21/c) is examined from both the geometrical and reticular point of view. The A3 twin axis, parallel to the screw diad axis of the parent (P) crystal, generates two twinned (T) individuals, mutually rotated by 120°. The structure of the resulting twinned interfaces are hypothesized, following the Hartman–Perdok method for determining the most stable surface profiles. The twin energy for each interface, evaluated by ab initio calculation, indicates that the activation energy for the nucleation of a three-dimensional (3D) twin can be hardly distinguished from the one needed to nucleate a single 3D crystal. Moreover, a triple monoclinic twin simulates the structure of a trigonal-hexagonal HAp single crystal and the growth morphology of a monoclinic twin gradually approaches the hexagonal habit as much as the twin grooves disappear during growth.

Diffusion-coupled molecular assembly: structuring of coordination polymers across multiple length scales.

Porous coordination polymers (PCPs) are an intriguing class of molecular-based materials because of the designability of framework scaffolds, pore sizes and pore surface functionalities. Besides the structural designability at the molecular scale, the structuring of PCPs into mesoscopic/macroscopic morphologies has attracted much attention due to the significance for the practical applications. The structuring of PCPs at the mesoscopic/macroscopic scale has been so far demonstrated by the spatial localization of coordination reactions on the surface of templates or at the phase boundaries. However, these methodologies have never been applied to the fabrication of solid-solution or multivariate metal-organic frameworks (MOFs), in which multiple components are homogeneously mixed. Herein, we demonstrate the structuring of a box-type superstructure comprising of a solid-solution PCP by integrating a bidirectional diffusion of multiple organic ligands into molecular assembly. The parent crystals of [Zn2(ndc)2(bpy)]n were placed in the DMF solution of additional organic component of H2bdc, and the temperature was rapidly elevated up to 80 °C (ndc = 1,4-naphthalenedicarboxylate, bpy = 4,4'-bipyridyl, bdc = 1,4-benzenedicarboxylate). The dissolution of the parent crystals induced the outward diffusion of components; contrariwise, the accumulation of the other organic ligand of H2bdc induced the inward diffusion toward the surface of the parent crystals. This bidirectional diffusion of multiple components spatially localized the recrystallization at the surface of cuboid parent crystals; therefore, the nanocrystals of a solid-solution PCP ([Zn2(bdc)1.5(ndc)0.5(bpy)]n) were organized into a mesoscopic box superstructure. Furthermore, we demonstrated that the box superstructures enhanced the mass transfer kinetics for the separation of hydrocarbons.

Anisotropic inplane spin correlation in the parent and Co-doped BaFe2As2: A neutron scattering study

Antiferromagnetic spin fluctuations were investigated in the normal states of the parent (x=0), under-doped (x=0.04) and optimally-doped (x=0.06) Ba(Fe1-xCox)2As2 single crystals using inelastic neutron scattering technique. For all the doping levels, quasi-two-dimensional antiferromagnetic fluctuations were observed as a broad peak localized at Q=(1/2,1/2,l). At lower energies, the peak shows an apparent anisotropy in the hk0 plane; longitudinal peak widths are considerably smaller than transverse widths. The anisotropy is larger for the higher doping level. These results are consistent with the random phase approximation (RPA) calculations taking account of the orbital character of the electronic bands, confirming that the anisotropic nature of the spin fluctuations in the normal states is mostly dominated by the nesting of Fermi surfaces. On the other hand, the quasi-two-dimensional spin correlations grow much rapidly for decreasing temperature in the x=0 parent compound, compared to that expected for nearly antiferromagnetic metals. This may be another sign of the unconventional nature of the antiferromagnetic transition in BaFe2As2.

Capturing snapshots of post-synthetic metallation chemistry in metal-organic frameworks.

Post-synthetic metallation is employed strategically to imbue metal-organic frameworks (MOFs) with enhanced performance characteristics. However, obtaining precise structural information for metal-centred reactions that take place within the pores of these materials has remained an elusive goal, because of issues with high symmetry in certain MOFs, lower initial crystallinity for some chemically robust MOFs, and the reduction in crystallinity that can result from carrying out post-synthetic reactions on parent crystals. Here, we report a new three-dimensional MOF possessing pore cavities that are lined with vacant di-pyrazole groups poised for post-synthetic metallation. These metallations occur quantitatively without appreciable loss of crystallinity, thereby enabling examination of the products by single-crystal X-ray diffraction. To illustrate the potential of this platform to garner fundamental insight into metal-catalysed reactions in porous solids we use single-crystal X-ray diffraction studies to structurally elucidate the reaction products of consecutive oxidative addition and methyl migration steps that occur within the pores of the Rh-metallated MOF, 1·[Rh(CO)2][Rh(CO)2Cl2].

Experimental Evaluation of Contact Secondary Nucleation Mechanisms

Contact secondary nucleation has vital importance in industrial crystallizers for reactions and purification, and it recently has been linked to contributing to biological homochirality emerged at an abiotic evolutionary stage. Despite years of studies, the mechanism of contact secondary nucleation has not been resolved whether contact secondary nuclei originate from parent crystals via microattrition or from semiordered solute clusters at the interface of parent crystals. This study takes advantage of the unique thermodynamic and kinetic properties of the glycine system that is capable of differentiating the origin of contact secondary nuclei based on the polymorph of secondary nuclei obtained. It is demonstrated using two different experimental designs that contact secondary nuclei could originate both from the semiordered solute molecules at the interface layer of existing crystals and from parent crystals themselves via the mechanism of microattrition depending on the magnitude of the contact force. When the contact force is relatively small (<2 N for γ-glycine), it is only sufficient to disturb the semiordered solute molecules at the interface layer, which could generate secondary nuclei; when the contact force exceeds a certain threshold (>2 N for γ-glycine), it not only disturbs the interface layer but also causes mechanical damages to the parent crystals.

Effect of Co2+ on the growth, optical properties and laser damage threshold of potential nonlinear optical l-alanine single crystal

Good transparent bulk single crystals of pure l-alanine (LA) and cobalt doped LA crystals have been synthesized and successfully grown by slow-cooling method from their aqueous solutions. The concentration of metal dopants in the mother solution with 0.5mol% for cobalt was carried out individually and crystals were obtained with well defined morphology. The as grown metal doped and pure single crystals were characterized by single crystal XRD studies which confirm that the incorporation of metallic dopants has not changed the basic structure of the parent crystal. The absorption of these crystals was analyzed and the result confirms that they possess low absorption in the range 230–1100nm. Fourier transform infrared (FTIR) spectroscopy was carried out to investigate the molecular vibrations of these crystals and to confirm the incorporation of the dopants. The thermal properties have been studied by TGA/DTA curves. The EDAX measurement and surface morphology were studied for pure and metal doped LA crystals. The second harmonic generation (SHG) signals were observed using Nd: YAG laser with fundamental wavelength of 1064nm in pure and metal doped crystals. The laser damage threshold was measured for pure and metal doped LA crystals and also tested by using a Q-switched Nd: YAG laser showed enhanced LDT value for metal (Co2+) doped LA crystal compared to pure LA crystal due to the metallic substitutions thus proving their useful candidature for nonlinear optical applications.

Selective catalytic cracking of n-hexane to propylene over hierarchical MTT zeolite

Catalytic cracking of naphtha over one-dimensional (1D) pore zeolite was targeted by using n-hexane as a model compound. Novel hierarchical H-ZSM-23 (MTT), a 1D pore zeolite, was specially designed to maximize propylene yield from catalytic cracking. Very high propylene-to-ethylene ratio of 2.5 was achieved. The ZSM-23 with mesopores displayed an enhanced deactivation resistance compared to microporous parent crystals. Hierarchical ZSM-23 was synthesized rapidly by applying microwave-assisted hydrothermal synthesis (MAHyS) followed by microwave-assisted alkaline treatment and moderate acid treatment. Pore volume of hierarchical ZSM-23 was improved considerably compared with the ones of parent crystals. Physico-chemical properties of hierarchical ZSM-23 were studied by characterization techniques such as XRD, FE-SEM, N2 adsorption–desorption, 27Al and 29Si MAS NMR, NH3-TPD, and TEM.

Ferromagnetism and spin-dependent transport inn-type Mn-doped bismuth telluride thin films

We describe a detailed study of the structural, magnetic, and magneto-transport properties of single-crystal, n-type, Mn-doped Bi2Te3 thin films grown by molecular beam epitaxy. With increasing Mn concentration, the crystal structure changes from the tetradymite structure of the Bi2Te3 parent crystal at low Mn concentrations towards a BiTe phase in the (Bi2Te3)m(Bi2)n homologous series. Magnetization measurements reveal the onset of ferromagnetism with a Curie temperature in the range 13.8 K - 17 K in films with 2 % - 10 % Mn concentration. Magnetization hysteresis loops reveal that the magnetic easy axis is along the c-axis of the crystal (perpendicular to the plane). Polarized neutron reflectivity measurements of a 68 nm-thick sample show that the magnetization is uniform through the film. The presence of ferromagnetism is also manifest in a strong anomalous Hall effect and a hysteretic magnetoresistance arising from domain wall scattering. Ordinary Hall effect measurements show that the carrier density is n-type, increases with Mn doping, and is high enough (> 2.8 x 10^{13} cm^{-2}) to place the chemical potential in the conduction band. Thus, the observed ferromagnetism is likely associated with both bulk and surface states. Surprisingly, the Curie temperature does not show any clear dependence on the carrier density but does increase with Mn concentration. Our results suggest that the ferromagnetism probed in these Mn-doped Bi2Te3 films is not mediated by carriers in the conduction band or in an impurity band.

In situ X-ray microdiffraction study of deformation-induced phase transformation in 304 austenitic stainless steel

The traditional phenomenological crystallographic theory of martensitic transformations can only explain the change in the shape and crystallographic orientation of a martensitic plate within a single parent crystal. It cannot predict the detailed transformation scenario for preferred selections of martensitic variants or the contributions of partial slip/twinning to local lattice distortion, especially in polycrystalline metals/alloys that exhibit grain-to-grain interactions throughout deformation-induced phase transformation. In this work, synchrotron-based X-ray microdiffraction was used to characterize changes in the local orientation, morphology and strain distribution inside individual martensitic plates, as well as the effect of parent orientation on variant selection in bulk polycrystalline 304 stainless steel (SS) during in situ uniaxial tensile loading at the low temperature of 210K. It was directly verified that the martensitic phase transformation in the studied 304 SS has two stages, transformation first from γ to ε in the nanoscaled lamella, and then from ε to α′ in the microbands. The selection of martensitic variants was predicted well by the minimum strain work criterion. Phase transformation-induced stress relaxation was evidenced by fluctuations in the (111) plane lattice strain accompanied by a strain gradient inside the martensitic plate, indicating a load transfer from the transformed grain to its neighbor. This leads to good stress/strain accommodation, as stresses can dissipate from the matrix into martensitic plates and nearby grains. Our experimental observations and theoretical analysis provide an in-depth understanding of the micromechanical behavior, particularly phase transformation-induced plasticity enhancement, of metals containing the metastable phase.

Synthesis, crystal growth and mechanical properties of Bismuth Silicon Oxide (BSO) single crystal

Bismuth Silicon Oxide (BSO) is an efficient material for piezo-electric and electro-optic applications. In this article, growth of BSO single crystal by high temperature Czochralski melt growth technique and its detailed mechanical characterization by Vickers microhardness, fracture toughness, crack propagation, brittleness index and yield strength have been reported. The raw material was synthesized by solid state reaction using the stoichiometric ratio of high purity bismuth tri-oxide and silicon di-oxide. The synthesized material was charged in the platinum crucible and then melted. The required rotation and pulling rate was optimized for BSO single crystal growth and good quality single crystal has been harvested after a time span of 5days. Powder X-ray diffraction analysis confirms the parent crystallization phase of BSO. The experimentally studied mechanical behavior of the crystal is explained using various theoretical models. The anisotropic nature of the crystals is studied using Knoop indentation technique.

Rational Design of Monocrystalline (InP)yGe5–2y/Ge/Si(100) Semiconductors: Synthesis and Optical Properties

In this work, we extend our strategy previously developed to synthesize functional, crystalline Si(5-2y)(AlX)y {X = N,P,As} semiconductors to a new class of Ge-III-V hybrid compounds, leading to the creation of (InP)(y)Ge(5-2y) analogues. The compounds are grown directly on Ge-buffered Si(100) substrates using gas source MBE by tuning the interaction between Ge-based P(GeH3)3 precursors and In atoms to yield nanoscale "In-P-Ge3" building blocks, which then confer their molecular structure and composition to form the target solids via complete elimination of H2. The collateral production of reactive germylene (GeH2), via partial decomposition of P(GeH3)3, is achieved by simple adjustment of the deposition conditions, leading to controlled Ge enrichment of the solid product relative to the stoichiometric InPGe3 composition. High resolution XRD, XTEM, EDX, and RBS indicate that the resultant monocrystalline (InP)(y)Ge(5-2y) alloys with y = 0.3-0.7 are tetragonally strained and fully coherent with the substrate and possess a cubic diamond-like structure. Molecular and solid-state ab initio density functional theory (DFT) simulations support the viability of "In-P-Ge3" building-block assembly of the proposed crystal structures, which consist of a Ge parent crystal in which the P atoms form a third-nearest-neighbor sublattice and "In-P" dimers are oriented to exclude energetically unfavorable In-In bonding. The observed InP concentration dependence of the lattice constant is closely reproduced by DFT simulation of these model structures. Raman spectroscopy and ellipsometry are also consistent with the "In-P-Ge3" building-block interpretation of the crystal structure, while the observation of photoluminescence suggests that (InP)(y)Ge(5-2y) may have important optoelectronic applications.

The Boson peak in supercooled water

We perform extensive molecular dynamics simulations of the TIP4P/2005 model of water to investigate the origin of the Boson peak reported in experiments on supercooled water in nanoconfined pores, and in hydration water around proteins. We find that the onset of the Boson peak in supercooled bulk water coincides with the crossover to a predominantly low-density-like liquid below the Widom line TW. The frequency and onset temperature of the Boson peak in our simulations of bulk water agree well with the results from experiments on nanoconfined water. Our results suggest that the Boson peak in water is not an exclusive effect of confinement. We further find that, similar to other glass-forming liquids, the vibrational modes corresponding to the Boson peak are spatially extended and are related to transverse phonons found in the parent crystal, here ice Ih.

Contact Secondary Nucleation as a Means of Creating Seeds for Continuous Tubular Crystallizers

The control of crystal size of any crystallization process is especially important in the pharmaceutical industry where small sizes are often desired. Seeding is often used as a method of controlling crystal size and suppressing primary nucleation in batch processes. The continuous mixed suspension mixed product removal crystallizers are self-seeded; however, crystal attrition and contact secondary nucleation due to crystal interaction with the impeller influence the crystal size. In this study, a nuclei generation device (nucleator) employing contact secondary nucleation is described. The nucleator consists of a “crossed” flow tube with four openings. Two of the openings are the inlet of supersaturated solution and the outlet of crystal slurry, respectively. The other two openings are for contact nucleation, where the parent crystal comes into contact with a platform under an applied stress. The rate of nucleation and the size of the crystals generated can be controlled by supersaturation (S = c/cs) and ...

Determination of the susceptibility of the shear modulus to the defect concentration in a metallic glass

The susceptibility of the shear modulus to the concentration of interstitialcy-like defects in a metallic glass has been determined using calorimetric data and in situ measurements of the shear modulus of glass and parent crystal at different heating rates. The obtained results provide further support for the Interstitialcy theory, which consistently connects equilibrium/supercooled liquid, glassy and crystalline states.

IgA associated vasculitis (IgAV) – a 5-year retrospective study

Single crystals of bis-thiourea zinc chloride (ZTC) doped with metal ion (Li+) possess excellent nonlinear optical properties. These crystals were grown by slow evaporation solution growth technique. The effect of Li+ dopant on the growth and properties of ZTC single crystal were investigated and reported. The grown crystals were crystallized in orthorhombic structure with non-centro symmetric space group Pn21a through the parent compound. The amount of dopant incorporated in the parent crystal was revealed by the inductively coupled plasma (ICP-OES) studies. The FT-IR spectroscopy study was done for finding and confirming the functional groups present in the compound. The UV–Visible spectral study was carried out to find the optical behavior and transparency nature of the grown crystal. TG/DTA measurements and Vickers microhardness measurements were traced to find out the thermal and mechanical stability of the grown crystals respectively. Using Nd:YAG laser, the Second harmonic generation (SHG) for the grown crystals were confirmed.

Habit modification of bis-thiourea zinc chloride (ZTC) semi organic crystals by impurities

Single crystals of bis-thiourea zinc chloride (ZTC) doped with metal ion (Li+) possess excellent nonlinear optical properties. These crystals were grown by slow evaporation solution growth technique. The effect of Li+ dopant on the growth and properties of ZTC single crystal were investigated and reported. The grown crystals were crystallized in orthorhombic structure with non-centro symmetric space group Pn21a through the parent compound. The amount of dopant incorporated in the parent crystal was revealed by the inductively coupled plasma (ICP-OES) studies. The FT-IR spectroscopy study was done for finding and confirming the functional groups present in the compound. The UV–Visible spectral study was carried out to find the optical behavior and transparency nature of the grown crystal. TG/DTA measurements and Vickers microhardness measurements were traced to find out the thermal and mechanical stability of the grown crystals respectively. Using Nd:YAG laser, the Second harmonic generation (SHG) for the grown crystals were confirmed.

Flexural Electromechanical Coupling: A Nanoscale Emergent Property of Boron Nitride Bilayers

The symmetry properties of atomically thin boron nitride (BN) monolayers endow them with piezoelectric properties, whereas the bulk parent crystal of stacked BN layers is not piezoelectric. This suggests potential for unusual electromechanical properties in the few layer regime. In this work, we explore this regime and discover that a bilayer consisting of two BN monolayers exhibits a strong mechanical coupling between curvature and electric fields. Using a mechanical model with parameters obtained from density functional theory, we find that these bilayers amplify in-plane piezoelectric displacements by exceedingly large factors on the order of 10(3)-10(4). We find that this type of electromechanical coupling is an emergent nanoscale property that occurs only for the case of two stacked BN monolayers.

Interrelationship between the shear modulus of a metallic glass, concentration of frozen-in defects, and shear modulus of the parent crystal

The Interstitialcy theory assumes that major structural defects defining the properties of glass are similar to dumbbell interstitials in crystalline metals. Within the framework of this approach, we showed that at a constant defect concentration, the temperature coefficient of the shear modulus of glass equals to that of the parent crystal, in agreement with the theory. Relaxation of the defect system leads to either positive or negative variation of this coefficient, depending on the sign of defect concentration change. A full map of the defect concentration for initial, relaxed, and quasi-equilibrium states of a Pd-based glass is presented.

Structural and Thermodynamic Insight into Solid State Phase Transition Mechanism of a 1,3,3′-Triketone

A study of a solid state phase transition in dipivaloyl(3-cyclopentylpropanoyl)methane was undertaken by a combination of crystallographic and calorimetric methods. The high temperature polymorph with two molecules in the asymmetric unit and a disordered cyclopentyl group undergoes a reversible phase transition into an ordered structure with a single molecule in the asymmetric unit. The transition temperature is −20.80 °C with a minimal hysteresis of 1 °C. The nucleation of the new phase was followed by differential scanning calorimetry and occurs in a wide temperature range starting from ca. 0.5 °C above and below the transition temperature, and the crystallographic orientation of the crystals of the nascent phase is to a high degree in agreement with that of the parent crystal.