Crystallographic Point Of View Research Articles

Understanding the Co-Poisoning Effect of Zr and Ti on the Grain Refinement of Cast Aluminum Alloys

The “co-poisoning” effect between Zr and Ti (derived from Al-Zr and Al-Ti-B master alloy additions) on the grain refinement of cast aluminum alloys is studied from a crystallographic atom matching viewpoint. The edge-to-edge matching (E2EM) model has been used to investigate the possible “poisoning” phase containing Zr/Ti, Al, and Fe in commercial grade aluminum alloys. The results show that Al3Ti is the most likely constituent to be poisoned due to the formation of an Al8Fe4Zr coating on its surface, since the Al8Fe4Zr phase has good crystallographic atom matching with Al3Ti, but not with the aluminum matrix. Meanwhile, the partial dissolution of Al3Zr nucleant particles to compensate for the loss of solute Zr aggravates the poisoning phenomenon. This proposed mechanism is consistent with most previous experimental observations and with existing practical solutions employed in the foundry.

Fabrication of tin monosulfide nanosheet arrays using laser ablation

We demonstrate the non-catalytic, low-temperature (∼200°C) synthesis of two-dimensional (2D) tin monosulfide (SnS) nanosheet arrays vertically aligned on the substrate by means of pulsed laser ablation (PLD) process. The prepared nanosheets were characterized using X-ray diffraction, Raman spectroscopy, field-emission electron microscopy, electron probe micro-analysis, and transmission electron microscopy (HRTEM). The growth mechanism of 2D morphological feature, which is widespread but very slim (∼10 nm), is further investigated in detail from the crystallographic point of view by observing highly-resolved lattice images taken from plane-normal and in-plane directions using focused ion-beam manipulation and high-resolution transmission microscopy.

Effect of annealing on formability and crystallographic textures of aluminium 5052 alloy sheets

Abstract In this work, forming and fracture limit diagrams have been experimentally evaluated for aluminium 5052 alloy sheet annealed at four different temperatures namely 200°C, 250°C, 300°C and 350°C. With the help of these diagrams, the safe range which avoids necking and fracture during forming of aluminium 5052 alloy sheets was examined and the effect of annealing temperature on this range and other parameters namely microstructure, tensile properties and formability parameters were studied. The forming limit diagrams of aluminium 5052 alloy sheets annealed under different temperatures were also examined with respect to the crystallographic texture point of view. The crystallographic textures were then correlated with normal anisotropy of the sheet metal. It was found that the formability of aluminium 5052 alloy annealed at 350°C possessed good formability, optimal texture and high normal anisotropy value.

Antimony Tuned Rhombohedral‐Orthorhombic Phase Transition and Enhanced Piezoelectric Properties in Sodium Potassium Niobate

It has been reported that the rhombohedral–orthorhombic low‐temperature polymorphic phase transition in (Na,K)NbO3 can be tuned close to room temperature by substituting Sb for Nb, such that enhanced piezoelectric properties are induced based on the theory of two‐phase coexistence. A diagram of phase structures changing with Sb content and temperature has been generalized for (Na,K)(Nb,Sb)O3 (NKNS) compositions. The thermal stability of piezoelectric properties of NKNS ceramics was evaluated considering the existence of successive phase transition above room temperature. The microstructure, dielectric, and ferroelectric properties of NKNS ceramics were discussed from a crystallographic point of view.

Mechanism of Acicular Ferrite Formation in Low Carbon Steel Ti–B Weld Metals with Different Oxygen Levels

Inclusions contributing to acicular ferrite nucleation were investigated from a crystallographic point of view to understand the formation mechanism for acicular ferrite microstructure in mild and low alloy steel weld metals.The samples with different oxygen content in Ti–B weld metal were prepared in this study. In those samples, intragranular acicular ferrite formation was observed from some inclusions and acicular ferrite had Kurdjumov–Sachs orientation relationship with austenite matrix. The inclusions contributing to acicular ferrite nucleation were multi-phase type consisting of amorphous phase and MnS. They were surrounded by a Ti-enriched layer. It was confirmed by selected area diffraction patterns and analysis of EDS that the Ti-enriched layer was TiO. The acicular ferrite had Baker–Nutting orientation relationship with TiO layer on the inclusion surface. The misfit was 3.0% at the interface between the acicular ferrite and TiO.Therefore, it is considered that the TiO on the inclusion surface contributes to the heterogeneous nucleation of acicular ferrite by small lattice misfit.

Effects of plating factors on morphology and appearance of electrogalvanized steel sheets

Because the lightness, the gloss and the press-formability of electrogalvanized steel sheets change depending on the morphology of deposited Zn, control of this factor is essential to improving these properties. The effects of plating factors on the morphology of deposited Zn were systematically discussed both from the crystallographic viewpoint of epitaxy between Zn and steel and from the electrochemical viewpoint of the overpotential for Zn deposition. Plating factors include crystal orientation of steel substrate, current density, flow rate, temperature, addition of inorganic compounds to the solution and pre-adsorption of organic compounds. These plating factors affect the overpotential for Zn deposition and epitaxy between Zn and steel. The crystal orientation index of the Zn basal plane and the platelet crystal size of Zn are decreased with increasing the overpotential for Zn deposition. They are also decreased with decreasing the epitaxy between Zn and steel, even when the overpotential is kept constant. When the overpotential for Zn deposition is increased, the surface roughness of deposited Zn increases because of an increase in the inclination of the Zn basal plane to the steel substrate. When the epitaxy between Zn and steel is decreased without changing the overpotential, the surface roughness is reduced due to the decrease in platelet crystal size of Zn, although the inclination of the Zn basal plane is somewhat increased. The lightness of deposited Zn is enhanced with decreasing the surface roughness of Zn.

High-pressure synthesis and characterization ofPrMn7O12polymorphs

We report the synthesis and the characterization of ${\text{PrMn}}_{7}{\text{O}}_{12}$, a new manganite with multiple (quadruple) perovskite structure of general chemical formula: $A{A}_{3}^{\ensuremath{'}}{B}_{4}{\text{O}}_{12}$. This family of manganites is extremely interesting and is attracting a great attention; thanks to its structural peculiarity (and complexity), it might help the comprehension of the ordering phenomena (charge, orbital, spin), which is one of the most challenging issues in the strongly electron correlated rare-earth oxides. Like the majority of the materials having similar structure, ${\text{PrMn}}_{7}{\text{O}}_{12}$ is a metastable compound, requiring high pressure synthesis. Contrary to other reported isostructural compounds, ${\text{PrMn}}_{7}{\text{O}}_{12}$ crystallizes in two different forms with rhombohedral $(R\text{\ensuremath{-}}3)$ and monoclinic $(I2/m)$ symmetry, the latter characterized by a distortion of the perovskite structure lattice that depends on the synthesis conditions. The approximate stability fields of the two ${\text{PrMn}}_{7}{\text{O}}_{12}$ phases have been defined in the $P/T$ space, allowing the synthesis of almost single phase samples functional to physical characterization. For the monoclinic phase we succeeded in the growth of crystals sufficiently large to perform structural refinement by single crystal x-ray diffraction data; the rhombohedral structure was instead refined by Rietveld method applied to powder x-ray diffraction data. Although the two phases differ slightly from the crystallographic point of view, physical characterizations reveal surprisingly different properties, in particular for what concerns the magnetic behavior. The differences of the two structures might be explained with a different electronic configuration of Mn, implying the partial occupation of ${\text{Mn}}^{3+}$ in low spin state on the $B$ site of the rhombohedral polymorph.

Room temperature ferrimagnetic thin films of the magnetoelectric Ga2−xFexO3

(0k0) oriented films of the magnetoelectric material Ga2−xFexO3 (0.8 ≤ x ≤ 1.4) have been grown by pulsed laser deposition on various substrates: the non conducting yttrium stabilized zirconia (YSZ) (001) and the conducting indium tin oxide (ITO) buffered YSZ(001) and single crystalline Pt(111) buffered YSZ(111). The films are ferrimagnetic for all compositions and their Curie temperature increases with x. For x = 1.4, their Curie temperature is above room temperature (370 K) and their room temperature saturation magnetization is 90 emu/cm3. The effect of the conducting substrates on both the crystalline and electrical properties of the films has been studied. The single crystalline Pt(111) buffered YSZ(111) substrates allow substantial improvements both on the crystallographic and electrical points of view with a reduction of the number of in-plane variants down to 3 and a decrease of the leakage current down to 10−5 A at 10 V. This work opens new perspectives for the integration of a room temperature ferrimagnetic magnetoelectric material in spintronic devices.

El cuarzo como material votivo y arquitectónico en el complejo funerario megalítico de Palacio III (Almadén de la Plata, Sevilla): Análisis contextual y mineralógico

This paper examines an assemblage of quartz objects, such as crystals (rock crystal and prase) and pebbles, that were found in two spatially and chronologically different contexts of the Palacio III megalithic complex (Almaden de la Plata, Seville, Spain) excavated by the universities of Seville and Southampton between 2001 and 2002. Firstly, these objects are described macroscopically from a mineralogical and crystallographic point of view. When possible, samples are studied by X-ray diffraction and SEM in order to determine their mineralogical and chemical composition. Secondly, other similar instances, in which quartz and rock crystal objects have been found among the grave goods of funerary contexts of southern Iberian, are described. Finally, we propose a series of interpretations for these objects, both from a functional as well as a symbolical perspective, assessing the significance of their presence in spatially discrete and chrono-culturally distant contexts.

Growth of β-Ga2O3 Single Crystals by the Edge-Defined, Film Fed Growth Method

The successful growth of 2-in. β-Ga2O3 crystals by the edge-defined, film fed growth (EFG) method was demonstrated. The optimization of growth conditions for larger single crystalline β-Ga2O3 is discussed in detail. The seeding conditions of temperature and neck width were found to be the most important factors to grow single crystals. X-ray rocking curve measurements of β-Ga2O3 crystals were conducted to estimate the dislocation densities of the grown crystals. Etch pit densities (EPDs) of the β-Ga2O3 crystals were also measured using KOH solution to measure the dislocation densities. The results were discussed combining with crystal growth parameters such as neck width to clarify the mechanisms of propagation and the origin of dislocations in crystals from phenomenological and crystallographic points of view.

Theoretical Investigation of the Uranyl Ion Sorption on the Rutile TiO2(110) Face

Canister integrity and radionuclide retention is of first importance for assessing the long-term safety of nuclear waste stored in engineered geologic depositories. Uranyl ion sorption on the TiO(2) rutile (110) face is investigated using periodic density functional theory (DFT) calculations. From experimental observations, only two uranyl surface complexes are observed and characterized. When the pH increases (from 1.5 to 4.5), the relative ratios of these two surface complexes are modified. From a crystallographic point of view, three sorption sites can be considered and have been studied with different protonation states of the surface to account for very acidic and low acidic conditions. The two surface complexes experimentally observed were calculated as the most stable ones, while the evolution of their sorption energies agrees with experimental data.

Comparative Behavior of Britholites and Monazite/Brabantite Solid Solutions during Leaching Tests: A Combined Experimental and DFT Approach

In the field of the specific immobilization of actinides, several phosphate-based ceramics have already been proposed as suitable candidates. Among them, britholite and monazite/brabantite (now called monazite/cheralite) solid solutions have been considered as serious candidates on the basis of several properties of interest. Although both matrices appear almost similar from a chemical point of view, their chemical behavior during leaching tests appear to be strongly different with normalized dissolution rates of typically (2.1 +/- 0.2) g.m(-2).day(-1) for Th-britholites (10(-1)M HNO(3), theta = 25 degrees C, dynamic conditions) and (2.2 +/- 0.2) 10(-5) g.m(-2).day(-1) for Th-brabantites (10(-1)M HNO(3), theta = 90 degrees C, dynamic conditions). To understand such difference from a crystallographic point of view, comparative leaching tests have been performed using either high or low renewal of the leachate. The results obtained clearly revealed a lower chemical durability of An-britholites compared to that of (Ln, Ca, An)-monazite/brabantite solid solutions. As a confirmation of this point, density functional theory calculations clearly showed some great differences in the cohesive energy of calcium in both crystal structures, which can explain this strong difference in the chemical durability of both materials.

A crystallographic texture perspective formability investigation of aluminium 5052 alloy sheets at various annealing temperatures

Formability, an important mechanical property of the sheet metal is strongly reliant on the crystallographic texture. Consequently deep drawability is also influenced. This paper deals with the perspective of crystallographic texture and its relevance with the formability of AA 5052 aluminium alloy sheet of 2 mm thickness annealed at four different temperatures namely 200 °C, 250 °C, 300 °C and 350 °C. Forming limit diagrams determined and plotted experimentally, their crystallographic textures obtained and their ODF plots prepared by X-ray diffraction were analyzed. The Forming limit diagrams (FLDs) of AA 5052 sheets annealed under different temperatures were examined with respect to the crystallographic texture point of view. The FLDs and crystallographic textures were then correlated with normal anisotropy of the sheet metal. It was found that the formability of aluminium alloy AA 5052 annealed at 350 °C possessed good formability, optimal texture and high normal anisotropy value.

Microstructural change of dislocation structure around SiGe/Si interface in SGOI wafer with ramping process

Microstructural change in SiGe/Si hetero interface of SiGe on insulator (SGOI) wafer with annealing was investigated by transmission electron microscopy. Misfit dislocations were observed in the specimen annealed at 1203 K. With further annealing above 1373 K, the straight shape of the misfit dislocations is change to the randomly curved and tangled with locking of the dislocation generated by the reaction of the two crossing misfit dislocations. Change in the morphology of the dislocation was also discussed from the crystallographic viewpoint.

Electrostatic force microscopy study on the domain switching properties of the Pb(Zr 0.2Ti 0.8)O 3 thin films with different crystallographic orientations for the probe-based data storage

The domain switching properties of the ferroelectric Pb(Zr 0.2Ti 0.8)O 3 (PZT) thin films with two types of crystallographic orientations were investigated by electrostatic force microscopy (EFM). The crystallographic orientations of the PZT thin films were random on the (1 1 1)Pt/MgO(1 0 0) and c-axis preferred on the (1 0 0)Pt/MgO(1 0 0), respectively. When dc bias was applied to the films for writing in micro-scale area, electrostatic force images showed that the domain switching was hard in the PZT thin films with random orientation, while the pattern could clearly be written in the PZT films with c-axis orientation. The differences in the domain switching properties of each PZT thin film were investigated in the crystallographic orientations point of view, and the domain switching dynamics were also measured by investigating the nano-sized dot switching behavior with respect to the width of the applied voltage pulse.

Coincidences in four dimensions

The coincidence site lattices (CSLs) of prominent four-dimensional lattices are considered. CSLs in three dimensions have been used for decades to describe grain boundaries in crystals. Quasicrystals suggest also looking at CSLs in dimensions d > 3. Here, we discuss the CSLs of the root lattice A 4 and the hypercubic lattices, which are of particular interest both from the mathematical and the crystallographic viewpoints. Quaternion algebras are used to derive their coincidence rotations and the CSLs. We make use of the fact that the CSLs can be linked to certain ideals and compute their indices, their multiplicities and encapsulate all this in generating functions in terms of Dirichlet series. In addition, we sketch how these results can be generalized for four-dimensional ℤ-modules by discussing the icosian ring.

Controllable Synthesis of Single-Crystalline Fe3O4 Polyhedra Possessing the Active Basal Facets

In the present paper, we report on the controllable preparation of single-crystalline Fe3O4 microrhombic dodecahedra possessing the active basal facets in high yield through a facile hydrothermal route. The growth mechanism of the microcrystals is discussed. From a crystallographic point of view, the shapes of the crystals are determined by the ratio of the growth rate along to directions. The pH values of the precursor solution strongly affected the morphologies of the products. When pH value was adjusted to 8–10, well-defined Fe3O4 truncated microrhombic dodecahedra exposing the active basal surfaces ({110}) with narrow size-distribution (<10%) were obtained. The sizes of the Fe3O4 truncated microrhombic dodecahedra are dependent upon the reaction time. The magnetic properties of the products are sensitive to the crystal size. The synthesized well-defined Fe3O4 microcrystals with active basal facets may have important applications in many fields.

Magneto-Structural Correlations in Cu(en)2SO4- a new Magnet with Two-Dimensional Triangular Arrangement of Cu(II) ions

Department of Inorganic Chemistry, Faculty of Science, Palacký University Křižkovskeho 10, 771 47 Olomouc, Czech Republic Cu(en)2SO4 (en = 1,2-diaminoethane) was synthesized and its crystal structure determined. From a crystallographic point of view, the compound might represent an example for the realization of a S = 1/2 Heisenberg magnet on a two-dimensional spatially anisotropic triangular lattice. Magnetic susceptibility and magnetization studies were performed to analyze the magneto-structural correlations and to characterize the magnetic subsystem of the present compound. The results indicate the presence of antiferromagnetic interactions between magnetic ions with zJ/kB ≈ −14.6 K and short-range order near 7 K.

A REVIEW ON PROCESS-RELATED CHARACTERISTICS OF PYRRHOTITE

In this review, the physical and chemical properties of the pyrrhotite group minerals are discussed, particularly their mineralogical behavior during mineral processing and phase transitions. Pyrrhotites are often associated with nickel ores and gold deposits. Consideration of the leaching processes of pyrrhotites focuses on the recovery of Ni and Au. The mechanisms of acid leaching are presented from physical, chemical, electrochemical, and crystallographic viewpoints. Other pyrrhotite processing techniques, including oxidation and flotation, are also included in this article.

Crystallography of recently developed grain refiners for Mg–Al alloys

The grain refinement potency of some recently reported grain refiners for Mg–Al based casting alloys, including TiC, TiN, SiC and TiB2, was investigated from a crystallographic viewpoint using the edge-to-edge matching model. The results show that TiB2 is more likely to form an energetically favourable orientation relationship with the Mg matrix, and it is predicted that TiB2 should have the best grain refinement efficiency. The other three compounds may also serve as heterogeneous nucleation sites, but are not likely to be as effective as TiB2. The present analysis provides a better rationale of the superior grain refinement performance of TiB2 compared with SiC.