Crystallographic Domains Research Articles

Recobrimento de Superfícies metálicas por Filmes de Titânia meso-macroporosa

RESUMO: O desenvolvimento de materiais porosos tem sido um dos objetivos da nanotecnologia. Existe uma necessidade cada vez mais real de entender os mecanismos que geram materiais auto-estruturados especificamente aqueles que se originam de moldes de partículas coloidais como: polímeros, sílica, titânia e silício. A importância desses moldes é produzir dispositivos com aplicações industriais como: células solares, dessalinizadores, baterias e cristais fotônicos. Uma das principais dificuldades encontradas na aplicação de partículas coloidais é produzí-las em larga escala com tamanho uniforme e depositá-las em superfícies planas para que possam cobrir homogeneamente um substrato formando domínios cristalográficos em escala micrométrica. O objetivo deste trabalho consiste em analisar a formação de filmes nanocristalinos de titânia em superfícies metálicas que foram caracterizados por Microscopia Eletrônica de Varredura (MEV). Os substratos metálicos eram placas comerciais de aço encontradas em lojas de material de construção. O substrato foi recoberto com esferas de látex infiltradas por solução precursora de titânia e posteriormente tratatado termicamente num forno tubular a 600 oC durante uma hora. Observa-se que o substrato metálico influencia a topografia do filme de titânia mesoporosa resultando em uma estrutura lamelar em que há possibilidade de interação com o meio externo. Estes resultados mostram que o substrato influencia diretamente a topografia da titânia mesoporosa que não é mais hexagonal com poros ordenados, mas lamelar possibilitando produção de membranas auto-limpantes com aplicação direta na construção civil.
 PALAVRAS-CHAVE: Partículas coloidais, Substrato metálico, Estrutura lamelar.

Structural, photocatalytic and electroconductive properties of bismuth-substituted CaMoO4

The Ca1−3xBi2xФxMoO4 system (0.025 ​≤ ​x ​≤ ​0.30, where Ф represents cation vacancies) was synthesized and studied. The 0.025 ​= ​x ​≤ ​0.15 compositions show a tetragonal defect scheelite structure. Powder X-ray and neutron diffraction patterns for compositions with 0.15 ​< ​x ​≤ ​0.225 exhibit a tetragonal supercell with asup ​≈ ​√5a, csup ​≈ ​c where a and c are the tetragonal scheelite cell parameters. Transmission electron microscopy shows that Ca0.4Bi0.4MoO4, crystals consist of three crystallographic domains: (1) defect scheelite; (2) tetragonal superlattice and (3) incommensurately modulated. Photocatalytic properties were studied using Rhodamine B water solutions under UV light. Catalytic activity increases with increasing Bi content. The conductivity of 0.15 ​< ​x ​≤ ​0.225 compositions is 10−7 to 10−8 ​S ​cm−1 in the range 500–650 ​°C, while compositions in the range 0.025 ​= ​x ​≤ ​0.15 show conductivity values from 10−3 to 10−8 ​S ​cm−1 from 500 to 800 ​°C.

Giant Field‐Induced Strain with Low Hysteresis and Boosted Energy Storage Performance under Low Electric Field in (Bi0.5Na0.5)TiO3‐Based Grain Orientation‐Controlled Ceramics

AbstractLead‐free dielectrics with both excellent strain behavior and superior energy‐storage feature are crucial toward providing desired performance for smart electrical devices, especially under harsh environmental conditions. Herein, it is demonstrated that giant strain response of ≈0.51% with small hysteresis of ≈29% and large recoverable energy density (≈1.6 J cm−3) under low electric field (120 kV cm−1), together with excellent stabilities against temperature, frequency, and cycling, can be simultaneously achieved in oriented (with 79.4% 〈00l〉 texture) (Bi0.5Na0.5)TiO3–BaTiO3–NaNbO3 (BNT–BT–NN) ceramics through integrating crystallographic texturing and domain engineering. Besides, a fast discharge rate of &lt;0.1 µs along with good thermal endurance in a wide temperature range can also be acquired. It is uncovered by piezoelectric force microscopy measurements that the formation of oriented microstructure greatly promotes the domain switching and mobility, producing the considerably easy ergodic relaxor to ferroelectric phase transition with concurrently improved strain and energy storage properties in grain orientation controlled BNT–BT–NN ceramics. This study offers a feasible and propagable guidance, i.e., crystallographic texturing and domain engineering, to develop new lead‐free dielectrics for both actuators and capacitors.

Morphology Control in van der Waals Epitaxy of Bismuth Telluride Topological Insulators

Bismuth telluride have regained significant attention as a prototype of topological insulator. Thin films of high quality have been investigated as a basic platform for novel spintronic devices. Low mobility of bismuth and high desorption coefficient of telluride compose a scenario where growth parameters have drastic effects on structural and electronic properties of the films. Recently [J. Phys. Chem. C 2019, 123, 24818−24825], a detailed investigation has been performed on the dynamics of defects in epitaxial films of this material, revealing the impact of film/substrate lattice misfit on the films’ lateral coherence. Very small lattice misfit (<0.05%) are expected to have no influence on quality of epitaxial system with atomic layers weakly bonded to each other by van der Waals forces, contrarily to what was observed. In this work, we investigate the correlation between lattice misfit and size and morphology of the film crystalline domains. Three-dimensional reciprocal-space maps of film Bragg reflections obtained with synchrotron X-rays are used to visualize the spatial conformation of the crystallographic domains through film thickness, while atomic force microscopy images provide direct information of the domains morphology at the film surface.

Tin Selenide Molecular Precursor for the Solution Processing of Thermoelectric Materials and Devices.

In the present work, we report a solution-based strategy to produce crystallographically textured SnSe bulk nanomaterials and printed layers with optimized thermoelectric performance in the direction normal to the substrate. Our strategy is based on the formulation of a molecular precursor that can be continuously decomposed to produce a SnSe powder or printed into predefined patterns. The precursor formulation and decomposition conditions are optimized to produce pure phase 2D SnSe nanoplates. The printed layer and the bulk material obtained after hot press displays a clear preferential orientation of the crystallographic domains, resulting in an ultralow thermal conductivity of 0.55 W m-1 K-1 in the direction normal to the substrate. Such textured nanomaterials present highly anisotropic properties with the best thermoelectric performance in plane, i.e., in the directions parallel to the substrate, which coincide with the crystallographic bc plane of SnSe. This is an unfortunate characteristic because thermoelectric devices are designed to create/harvest temperature gradients in the direction normal to the substrate. We further demonstrate that this limitation can be overcome with the introduction of small amounts of tellurium in the precursor. The presence of tellurium allows one to reduce the band gap and increase both the charge carrier concentration and the mobility, especially the cross plane, with a minimal decrease of the Seebeck coefficient. These effects translate into record out of plane ZT values at 800 K.

Two types of magnetic shape-memory effects from twinned microstructure and magneto-structural coupling in Fe1+yTe

A detailed experimental investigation of Fe1+y Te (y = 0.11, 0.12) using pulsed magnetic fields up to 60 T confirms remarkable magnetic shape-memory (MSM) effects. These effects result from magnetoelastic transformation processes in the low-temperature antiferromagnetic state of these materials. The observation of modulated and finely twinned microstructure at the nanoscale through scanning tunneling microscopy establishes a behavior similar to that of thermoelastic martensite. We identified the observed, elegant hierarchical twinning pattern of monoclinic crystallographic domains as an ideal realization of crossing twin bands. The antiferromagnetism of the monoclinic ground state allows for a magnetic-field-induced reorientation of these twin variants by the motion of one type of twin boundaries. At sufficiently high magnetic fields, we observed a second isothermal transformation process with large hysteresis for different directions of applied field. This gives rise to a second MSM effect caused by a phase transition back to the field-polarized tetragonal lattice state.

Intra-grain polarized infrared spectroscopy realized in domain-engineered Zn2GeO4 ceramics

Intra-grain infrared spectroscopy was carried out on a domain-engineered ceramic with abnormally large grains. The model system used was a polycrystalline Zn2GeO4 ceramic sample, with a rhombohedral R3¯ crystal structure and giant grain microstructure (50–350 μm). The micro-infrared spectra unveiled preferential crystal orientations for the different grains. Polarized spectra revealed well-defined crystallographic domains inside the ceramic grains. Appropriate crystallographic planes for full assignment of the infrared modes were found by polarized infrared light. This allowed the first realization of a polarization-resolved symmetry assignment of an as-grown ceramic material. A sound description of the polar phonon features of rhombohedral Zn2GeO4 is then presented. Also, an infrared spectroscopic mapping of the crystallographic domains inside the ceramic grains is demonstrated.

Ultrafast Relativistic Electron Nanoprobes

One of the frontiers in electron scattering is to couple ultrafast temporal resolution with highly localized probes to investigate the role of microstructure on material properties. Here, taking advantage of the high average brightness of our electron source, we demonstrate the generation of ultrafast relativistic electron beams with picometer-scale emittance and their ability to probe nanoscale features on materials with complex microstructures. The electron beam is tightly focused at the sample plane by a custom in-vacuum lens system, and its evolution around the waist is accurately reconstructed. We then use the focused beam to characterize a Ti-6 wt% Al polycrystalline sample by correlating the diffraction and imaging modality, showcasing the capability to locate grain boundaries and map adjacent crystallographic domains with sub-micron precision. This work provides a paradigm for ultrafast electron instrumentation, enabling characterization techniques such as relativistic ultrafast electron nano-diffraction and ultrafast scanning transmission electron microscopy.

Magnetic Traits in CoO‐Core@CoFe2O4‐shell Like Nanoparticles

AbstractAntiferromagnetic (AF) CoO pseudo‐single crystals 125±20 nm in diameter were prepared by forced hydrolysis in polyol and used as seeds to grow a poly‐ and nano‐crystalline (5 nm in diameter) ferrimagnetic (F) CoFe2O4 shell. Transmission electron microscopy (TEM) showed a certain epitaxy between the face‐centered cubic lattices of the AF rock‐salt core and the F spinel shell. Magnetometry measurements do not evidence any exchange bias feature between the two phases in direct contact. The hysteresis loops recorded between 7 and −7 T after cooling the composite particles from 400 K (between the Néel and the Curie temperatures of the AF and F phases, respectively) to 5 K, with and without a cooling magnetic field (μ0HFC=+7 T), are the same, meaning that the AF core does not allow any spin pinning on the CoFe2O4 nanocrystals. Nevertheless, differences exist between these magnetic data and those collected on two CoFe2O4 reference particles: the low temperature coercive field of the composite is between those of 5 nm sized single‐crystals and their assembly as submicrometer polycrystals. This order was also observed for the blocking temperature, although the constituting CoFe2O4 nanocrystals of all these particles, the composite and the two references, were the same. Advanced analysis by X‐ray diffraction and TEM established that the coherent crystallographic domain length of the ferrite phase and the magnetic behavior of the three systems are interdependent. Depending on the growth conditions of the CoFe2O4 phase, a relative epitaxy between the nanocrystals may exist. It is much greater in the polycrystalline CoFe2O4 particles than in their CoO−CoFe2O4 core‐shell counterparts, and does not occur in free single crystal CoFe2O4 particles.

The effects of dislocations on crystallographic twins and domain wall motion in magnetite at the Verwey transition

Pure magnetite experiences a first-order phase transition (the Verwey transition) near 120–125 K wherein the mineral’s symmetry changes from cubic to monoclinic. This transformation results in the formation of fine-scale crystallographic twins and is accompanied by a profound change in magnetic properties. The Verwey transition is critical to a variety of applications in environmental magnetism and paleomagnetism because its expression is diagnostic for the presence of stoichiometric (or nearly stoichiometric) magnetite and cycling through the Verwey transition tends to remove the majority of multidomain magnetic remanence. Internal and external stresses demonstrably affect the onset of the Verwey transition. Dislocations create localized internal stress fields and have been cited as a possible source of an altered Verwey transition in deformed samples. To further investigate this behavior, a laboratory-deformed magnetite sample was examined inside a transmission electron microscope as it was cooled through the Verwey transition. Operating the microscope in the Fresnel mode of Lorentz microscopy enabled imaging of the interactions between dislocations, magnetic domain walls, and low-temperature crystallographic twin formation during the phase transition. To relate the observed changes to more readily measurable bulk sample magnetic behavior, low-temperature magnetic measurements were also taken using SQUID magnetometry. This study allows us, for the first time, to observe the Verwey transition in a defect-rich area. Dislocations, and their associated stress fields, impede the development of monoclinic magnetite twin structures during the phase transition and increase the remanence of a magnetite sample after cooling and warming through the Verwey transition.

Ultrathin Ni nanowires embedded in SrTiO3 : Vertical epitaxy, strain relaxation mechanisms, and solid-state amorphization

Strain is a key parameter affecting the physical properties of heterostructured thin films and nanosized objects. Generally, the design of application-optimized hybrid structures requires good structural compatibility between the involved phases. However, when controlled appropriately, lattice mismatch can turn from a detrimental to a beneficial property, enabling further functionality tuning. Due to their large heterointerface, nanocolumnar composites are an ideal test bed for such strain engineering approaches, but coupling mechanisms at vertical interfaces are still poorly understood. In the present paper, we therefore present a detailed analysis of ultrathin Ni nanowires, with diameters between 1.7 nm and 5.3 nm, vertically epitaxied in a ${\mathrm{SrTiO}}_{3}$/${\mathrm{SrTiO}}_{3}$(001) matrix. Using a combination of x-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and x-ray absorption spectroscopy (XAS) measurements, we unveil peculiar structural features of this hybrid system. We show that the axial deformation of the nanowires depends on their diameter and that their radial strain differs sensitively from the value expected when considering the Poisson ratio. We also provide evidence for the existence of a relaxation mechanism consisting in a slight tilting of crystallographic nanowire domains which reduces the misfit at the Ni-${\mathrm{SrTiO}}_{3}$ heterointerface. This, in turn, induces significant structural disorder and results in a successive amorphization of the metallic phase upon diameter reduction of the nanowires.

The effect of crystal distortion and domain structure on piezoelectric properties of BiFeO3 thin films

BiFeO3 films are promising piezoelectric materials for vibration energy harvesting. In this study, the effects of the crystallographic symmetry and domain structure, which significantly depends on film thickness owing to the strain from the substrate, on the direct piezoelectric properties of (100) BiFeO3 epitaxial films were investigated. The BiFeO3 epitaxial films with thicknesses from 100 to 1000 nm were grown by rf magnetron sputtering. The crystal and domain structures of the films were characterized by reciprocal space mapping of X-ray diffraction and piezoelectric force microscopy. It was found that the highest e31,f coefficient of −3.9 C/m2 was obtained on the 600-nm-thick film, which has an intermediate structure between tetragonal and rhombohedral. This suggests that the phase transition by lattice relaxation is effective for improving the piezoelectric properties of BiFeO3 films.

Stabilization of Epitaxial α-Fe2O3 Thin Films Grown by Pulsed Laser Deposition on Oxide Substrates

We have grown epitaxial incommensurate α-Fe2O3 thin films on α-Al2O3(0001), SrTiO3(111), and LaAlO3(001) substrates, identifying hematite as single iron oxide phase stabilized. We demonstrate that a different lattice coupling behavior as a function of the selected oxide substrate mediates the epitaxial character. Single-oriented α-Fe2O3(0001) layers are obtained on α-Al2O3(0001) and SrTiO3(111) substrates, whereas on the LaAlO3(001) substrate, the hematite layer is found to grow along the r-plane to adapt its hexagonal lattice on the cubic lattice of the substrate, evidencing a single-oriented (1102) layer. In the film plane, crystallographic axes of α-Fe2O3(0001) are collinear with the α-Al2O3(0001) ones, while a rotation of 30° is found between those of α-Fe2O3(0001) and SrTiO3(111). On LaAlO3(001), α-Fe2O3(1102) adopts an in-plane orthorhombic structure rotated 45° respect to the substrate lattice. The crystallographic domain size and the crystalline order are dependent on the incommensurate lattice ...

Temperature-Dependent Evolution of Crystallographic and Domain Structures in (K,Na,Li)(Ta,Nb)O3 Piezoelectric Single Crystals.

(K,Na)NbO3-based ferroelectric single crystals have recently undergone a substantial development, resulting in improved crystal quality and large piezoelectric coefficients, exceeding 700 pC/N, over a broad temperature range. However, further development necessitates a detailed understanding of the mechanisms defining the domain structure and its temperature evolution. This paper presents the investigation into the crystallographic structure and domain configurations of a (K,Na,Li)(Ta,Nb)O3 single crystal over a broad temperature range. The crystal was grown by the submerged-seed solution growth technique and investigated using in situ transmission electron microscopy, X-ray diffraction, dielectric measurements, and polarized light microscopy. The lattice distortion, structural phase transitions, and domain configurations are reported. A transition from the lamellar orthorhombic to the rectangular tetragonal domain structure is observed upon heating. Moreover, the milky optical appearance of the crystal was investigated and found to result from the presence of regions with different domain configurations and domain sizes. The formation of these regions is related to the growth defects, which govern the domain formation when cooling below the Curie temperature.

Research Update: Focused ion beam direct writing of magnetic patterns with controlled structural and magnetic properties

Focused ion beam irradiation of metastable Fe78Ni22 thin films grown on Cu(100) substrates is used to create ferromagnetic, body-centered cubic patterns embedded into paramagnetic, face-centered-cubic surrounding. The structural and magnetic phase transformation can be controlled by varying parameters of the transforming gallium ion beam. The focused ion beam parameters such as the ion dose, number of scans, and scanning direction can be used not only to control a degree of transformation but also to change the otherwise four-fold in-plane magnetic anisotropy into the uniaxial anisotropy along a specific crystallographic direction. This change is associated with a preferred growth of specific crystallographic domains. The possibility to create magnetic patterns with continuous magnetization transitions and at the same time to create patterns with periodical changes in magnetic anisotropy makes this system an ideal candidate for rapid prototyping of a large variety of nanostructured samples. Namely, spin-wave waveguides and magnonic crystals can be easily combined into complex devices in a single fabrication step.

ICNME 2018: The 6th International Conference on Nanomaterials and Materials Engineering

PrefaceWith great pleasure, we introduce the Proceedings of 2018 6th International Conference on Nanomaterials and Materials Engineering (ICNME 2018) which provides a lively knowledge sharing forum that reports the latest development of research and application pertaining to Nanomaterials and Materials Engineering. ICNME 2018 offers an extensive program of interest to academia, government and industry. Great presentations have been delivered that allow effective knowledge dissemination, as well as enhancing relevant professional practices and skills.The objective of ICNME 2018 will always be bringing together a large group of researchers, scientists, academics, and engineers in the area of Nanomaterials and Materials Engineering from all over the world to share ideas not only about the technical interests, but also cross culture and history.This proceedings of ICNME 2018 presents the accepted papers, where the submitted papers are from universities, research institutes and industries. The submitted papers have been gone through a rigorous review and the papers are selected based on quality and relevancy to the conference. The volume tends to present to the readers the recent advancement in the field of Nanomaterials and Nanotechnology; Biomaterials and Biomedical Engineering; Ceramic and Glass Materials; Computational Material Science; Coupling of Multiple Ferroic Order Parameters; Crystal Defect Engineering; Crystallographic Domain Engineering; etc.We would like to thank all the authors who have contributed to this volume and also to reviewers, speakers, chairpersons, sponsors and all the conference participants for their commitment, hard work and support to ICNME 2018.ICNME 2018 CONFERENCE CHAIRMarch 30, 2018

Ultrahigh-resolution nonlinear optical imaging of the armchair orientation in 2D transition metal dichalcogenides

We used nonlinear laser scanning optical microscopy to study atomically thin transition metal dichalcogenides (TMDs) and revealed, with unprecedented resolution, the orientational distribution of armchair directions and their degree of organization in the two-dimensional (2D) crystal lattice. In particular, we carried out polarization-resolved second-harmonic generation (PSHG) imaging for monolayer WS2 and obtained, with high-precision, the orientation of the main crystallographic axis (armchair orientation) for each individual 120 × 120 nm2 pixel of the 2D crystal area. Such nanoscale resolution was realized by fitting the experimental PSHG images, obtained with sub-micron precision, to a new generalized theoretical model that accounts for the nonlinear optical properties of TMDs. This enabled us to distinguish between different crystallographic domains, locate boundaries and reveal fine structure. As a consequence, we can calculate the mean orientational average of armchair angle distributions in specific regions of interest and define the corresponding standard deviation as a figure-of-merit for the 2D crystal quality.

Charge-Stripe Order and Superconductivity in Ir1\u2212xPtxTe2

A combined resistivity and hard x-ray diffraction study of superconductivity and charge ordering in Ir Ir1−xPtxTe2, as a function of Pt substitution and externally applied hydrostatic pressure, is presented. Experiments are focused on samples near the critical composition xc ~ 0.045 where competition and switching between charge order and superconductivity is established. We show that charge order as a function of pressure in Ir0.95Pt0.05Te2 is preempted — and hence triggered — by a structural transition. Charge ordering appears uniaxially along the short crystallographic (1, 0, 1) domain axis with a (1/5, 0, 1/5) modulation. Based on these results we draw a charge-order phase diagram and discuss the relation between stripe ordering and superconductivity.

Change in the Crystallite Orientation of Poly(ethylene oxide)/Cellulose Nanofiber Composite Films.

The crystallite orientation and crystallographic domain structure of poly(ethylene oxide) (PEO) in cellulose nanofiber-incorporated (CNF-incorporated) PEO films developed for packaging materials were observed using wide-angle X-ray diffraction for different CNF filling ratios. When a CNF filling ratio of <10 wt % was used, the molecular chains in the PEO crystallite region were oriented in a direction perpendicular to the surface of the film; however, when the ratio was >50 wt %, the PEO molecular chains were oriented in a direction parallel to the surface of the film. The fiber axis of the CNFs became parallel to the surface of the PEO/CNF composite film when the filling ratio was >25 wt %. The change in the orientation of the PEO crystals occurred because increasing the amount of CNF in the composite films decreased the space in which the PEO could be crystallized. Furthermore, the hydrogen bonds between the PEO and the CNF may behave as crystallization nuclei for the PEO. Our results thus pave the way toward the development of packaging materials that are more impermeable to gases than the current materials.

Exceptionally High Piezoelectric Coefficient and Low Strain Hysteresis in Grain-Oriented (Ba, Ca)(Ti, Zr)O3 through Integrating Crystallographic Texture and Domain Engineering.

Both low strain hysteresis and high piezoelectric performance are required for practical applications in precisely controlled piezoelectric devices and systems. Unfortunately, enhanced piezoelectric properties were usually obtained with the presence of a large strain hysteresis in BaTiO3 (BT)-based piezoceramics. In this work, we propose to integrate crystallographic texturing and domain engineering strategies into BT-based ceramics to resolve this challenge. [001]c grain-oriented (Ba0.94Ca0.06)(Ti0.95Zr0.05)O3 (BCTZ) ceramics with a texture degree as high as 98.6% were synthesized by templated grain growth. A very high piezoelectric coefficient (d33) of 755 pC/N, and an extremely large piezoelectric strain coefficient (d33* = 2027 pm/V) along with an ultralow strain hysteresis (Hs) of 4.1% were simultaneously achieved in BT-based systems for the first time, which are among the best values ever reported on both lead-free and lead-based piezoceramics. The exceptionally high piezoelectric response is mainly from the reversible contribution, and can be ascribed to the piezoelectric anisotropy, the favorable domain configuration, and the formation of smaller sized domains in the BCTZ textured ceramics. This study paves a new pathway to develop lead-free piezoelectrics with both low strain hysteresis and high piezoelectric coefficient. More importantly, it represents a very exciting discovery with potential application of BT-based ceramics in high-precision piezoelectric actuators.