Zinc Single Crystals Research Articles

Grain Refinement of Pure Zinc Single Crystals with Different Crystal Orientations during a Single Pass of ECAP

Grain Refinement of Pure Zinc Single Crystals with Different Crystal Orientations during a Single Pass of ECAP

Perspective on Development of Piezoelectric Micro-Power Generators

Anthropogenetic environmental deterioration and climate change caused by energy production and consumption pose a significant threat to the future of humanity. Renewable, environmentally friendly, and cost-effective energy sources are becoming increasingly important for addressing future energy demands. Mechanical power is the most common type of external energy that can be converted into useful electric power. Because of its strong electromechanical coupling ability, the piezoelectric mechanism is a far more successful technique for converting mechanics energy to electrical energy when compared to electrostatic, electromagnetic, and triboelectric transduction systems. Currently, the scientific community has maintained a strong interest in piezoelectric micro-power generators because of their great potential for powering a sensor unit in the distributed network nodes. A national network usually has a large mass of sensor units distributed in each city, and a self-powered sensor network is eagerly required. This paper presents a comprehensive review of the development of piezoelectric micro-power generators. The fundamentals of piezoelectric energy conversion, including operational modes and working mechanisms, are introduced. Current research progress in piezoelectric materials including zinc oxide, ceramics, single crystals, organics, composite, bio-inspired and foam materials are reviewed. Piezoelectric energy harvesting at the nano- and microscales, and its applications in a variety of fields such as wind, liquid flow, body movement, implantable and sensing devices are discussed. Finally, the future development of multi-field coupled, hybrid piezoelectric micropower generators and their potential applications are discussed.

Selective sensing performance of UV-activated ZnO nanowires decorated with Ir and Rh nanoparticles

Single-crystal zinc oxide (ZnO) nanowires (NWs) were synthesized through self-assembly hydrothermal reaction and decorated with oxidative and reductive catalytic active sites to tailor their gas sensing selectivity. The sensing performances of the developed materials were investigated under ultraviolet-light emitting diode (UV-LED) irradiation against low concentrations of nitrogen dioxide (NO2) and ammonia (NH3) gases, as oxidizing and reducing gas representatives, respectively. The growth of NWs towards the hexagonal c-axis was demonstrated, where presence of Rh3d and Ir4f active sites on the surface of ZnO NWs was observed. The sensing performance of the surface modified ZnO NWs was enhanced significantly, compared with that of the pristine ZnO NWs. The Rh-decorated ZnO NWs sensor exhibited superior performance in the detection of NO2, while the Ir sites promoted the oxidative reaction in the presence of NH3, attributed to the Fermi level of the metal-decorated films under UV irradiation.

Electronic and thermal properties of Ag-doped single crystal zinc oxide via laser-induced technique

The doping of ZnO has attracted lots of attention because it is an important way to tune the properties of ZnO. Post-doping after growth is one of the efficient strategies. Here, we report a unique approach to successfully dope the single crystalline ZnO with Ag by the laser-induced method, which can effectively further post-treat grown samples. Magnetron sputtering was used to coat the Ag film with a thickness of about 50 nm on the single crystalline ZnO. Neodymium-doped yttrium aluminum garnet (Nd:YAG) laser was chosen to irradiate the Ag-capped ZnO samples, followed by annealing at 700 °C for two hours to form ZnO:Ag. The three-dimensional (3D) information of the elemental distribution of Ag in ZnO was obtained through time-of-flight secondary ion mass spectrometry (TOF-SIMS). TOF-SIMS and core-level x-ray photoelectron spectroscopy (XPS) demonstrated that the Ag impurities could be effectively doped into single crystalline ZnO samples as deep as several hundred nanometers. Obvious broadening of core level XPS profiles of Ag from the surface to depths of hundred nms was observed, indicating the variance of chemical state changes in laser-induced Ag-doped ZnO. Interesting features of electronic mixing states were detected in the valence band XPS of ZnO:Ag, suggesting the strong coupling or interaction of Ag and ZnO in the sample rather than their simple mixture. The Ag-doped ZnO also showed a narrower bandgap and a decrease in thermal diffusion coefficient compared to the pure ZnO, which would be beneficial to thermoelectric performance.

Morphological of Zinc Ferrite Nanostructure Using the Hydrothermal Synthesis

Over the last two decades, many methods for synthesizing various ZnFe2O4 nanostructures of uniform size and shape, such as nanospheres, nanoflowers, nanorods, and nanotubes, have been developed. It seems challenging to investigate a practical and cost-effective method to synthesize cubic ZnFe2O4 magnetite with cubic morphological properties in an aqueous solution. The morphology of zinc ferrite nanostructures is mostly random and non-uniform. The objective of this study is to create reasonably uniform single-crystal zinc ferrite nanocubes. The hydrothermal method was used to successfully sample zinc ferrite by varying the amount of (En) ethylenediamine (0 - 2.4 mL) in the solution. The outcomes demonstrated that the nanocubes, with a particle size of nearly 48 nm, had a more uniform morphology than other samples. The morphology and dimensions of the samples were examined using scanning electron microscopy in conjunction with energy dispersion X-ray spectroscopy.

Orientation Dependence on Bending Deformation Behavior of Pure Zinc Single Crystals

Three-point bending tests were performed on pure zinc single crystals with different crystal orientations to investigate orientation dependence on bending deformation behavior. With basal planes parallel to the neutral planes, the specimens deformed due to basal slips and formed a gull shape after deformation. On the other hand, specimens whose neutral planes are perpendicular to the basal planes and neutral axes are perpendicular to [0001] deformed due to second order pyramidal 〈c + a〉 slips, {1012} twinning and basal slips within {1012} twins, displaying a V shape. The bending deformation behavior of pure zinc single crystals was found to show strong orientation dependence. Also, the bending deformation behavior of pure zinc single crystals was found to differ from that of pure magnesium single crystals when the neutral plane and neutral axis are respectively perpendicular to the basal planes and [0001].

Mechanism of quasi-viscous flow of zinc single crystals

Abstract This paper reports the results of mechanical investigations (tensile and relaxation tests), geometrical measurements as well as macro- and microscopic (slip traces) observations of zinc single crystals in the ‘hard’ orientation (from the line [1120] – [1010] of the standard triangle) tested in the temperature range 523– 673 K. Consideration of the experimental data lead to the conclusion that the quasi-viscous flow of crystals results from localized coarse slip in the basal system occurring in the structure of uniformly distributed slip in the 1st order prismatic (and/or the 1st order pyramidal) systems. The proposed mechanism explains the high strain-rate sensitivity and the ‘jerky’ character of the flow of the crystals.

New large-strain FFT-based formulation and its application to model strain localization in nano-metallic laminates and other strongly anisotropic crystalline materials

This paper presents a new robust large-strain (LS) elasto-viscoplastic (EVP) formulation based on Fast Fourier Transforms (FFTs) for the prediction of the micro-mechanical response and microstructure evolution of polycrystalline and multiphase materials, with emphasis on the effect of strong crystallographic and/or morphologic anisotropy on localization of plastic deformation. The novel LS-EVPFFT formulation allows treatment of complex initial geometries and large deformations considering three grids of material points: a regular grid in the reference configuration, where FFTs can be performed; an irregular grid in the initial configuration, created by applying a stress-free displacement field to the reference regular grid; and an irregular grid in the current configuration, undergoing large strains and rotations as the material is loaded. Further numerical stability of the new formulation also required the use of a novel expression for the discrete modified Green's operator, which reduces spurious field oscillations. After presenting and validating the new formulation by comparison with pre-existing implementations and analytical solutions, LS-EVPFFT is applied to the prediction of slip and kink bands formation in polycrystalline columnar ice, and kink bands in single crystal zinc wires, showing good agreement with classic experiments. Finally, the model is used to study kink band formation during compression of Cu–Nb nano-metallic laminates (NMLs), in which accurate treatment of the complex geometry associated with the tortuosity of interfaces and large deformations become critical, showing consistency with corresponding micropillar experiments.

Моделирование напряженного состояния в преградах из анизотропных материалов

To study the properties of anisotropic materials, a mathematical model is proposed that accounts for the anisotropy of elastic and plastic properties, as well as the anisotropy of “thermal” and “cold” components of pressure. The model is applied in a threedimensional simulation of the deformation of an HCP-single-crystal barrier under impact loading by an aluminum impactor. The numerical simulation results are obtained using the dynamic finite element method with a difference scheme modified to account for the anisotropy of “cold” and “thermal” pressure components. To simulate the anisotropy of the stress deviator in the region of elastic deformations, generalized Hooke's law is used, while in the region of plastic deformations, the Mises-Hill plasticity function (Hill48) is used with account for the anisotropy of elastic properties and anisotropy of the Gruneisen coefficient. The experimentally and numerically obtained velocity profiles of the back surfaces of single-crystal zinc barriers during the spall fracture are compared with each other. When the impact loading direction coincides with [0001] axis, the elastic precursor is not observed on the velocity profile calculated numerically, which is the same for the one derived experimentally. This effect may be explained only with the use of anisotropic pressur.

Post-Annealing Effects on the Structure and Semiconductor Performance of Nanocrystalline ZnTe Thin Films Electrodeposited from an Aqueous Solution Containing Citric Acid

Using the potentiostatic electrodeposition technique, zinc telluride nanocrystalline thin films and an array of nanowires were synthesized in a citric acid bath. Electrodeposited zinc telluride thin films with stoichiometric compositions were obtained at a cathode potential of approximately −0.8 V versus Ag/AgCl, which was in a more noble region compared with the equilibrium potential of zinc. The average thickness of the zinc telluride thin films was approximately 3 μm, and the average growth rate was approximately 3 nm s−1. The as-deposited zinc telluride thin films had an amorphous phase with a black tint. By contrast, the zinc telluride thin films annealed at 683 K had a crystalline phase with a reddish-brown tint. The electrodeposited single-phase zinc telluride exhibited an optical absorption performance in a wavelength region that was shorter than 559 nm. At the annealing temperature of 683 K, the zinc telluride films exhibited an energy band gap of 2.3 eV, which was almost identical to that of single-crystal zinc telluride. The resistivity of the as-deposited amorphous-like zinc telluride thin films was approximately 2 × 105 Ω·m, whereas that of the samples annealed at 683 K was around 2 × 103 Ω·m, which was smaller than that of single-crystal zinc telluride. A three-dimensional nanostructure constructed with the zinc telluride nanowire array was also demonstrated using a template synthesis technique.

Investigations on the surface, thermo-electrical and mechanical properties of ZBG crystal for optoelectronics applications

The low temperature solution growth method was adopted for growing semi organic single crystal zinc boro glutrate (ZBG). The surface morphology was investigated by SEM analysis. Analysis of microhardness has been done, measurement of the Vickers hardness number Hv. Dielectric studies show a decrease in dielectric loss and dielectric constant with an increase in frequency and a constant value in the higher frequencies, suggesting that the crystal is also of good optical quality in nature.

Mechanism of kink band formation in zinc single crystals

Abstract This paper is focused on the mechanism of kink band formation. In the general case, lattice rotation in a kink band may be realized by two sequentially activated simple elastic shears in nearly perpendicular planes. In the case of zinc crystals, compressed along (0001) plane at the temperature 523 K, the first shear may result from stress-induced temporary lattice instability (movement of atoms towards metastable positions in tetrahedric holes), while the second shear occurring along a temporary ‘new-positioned’ basal plane immediately ‘rebuilds’ the stable lattice.

Fabrication of single crystal fiber-like ZnO/polyvinyl alcohol (PVA) films using the spray-drying approach

We report a rapid, facile, and cost-effective approach to fabricating single-crystal zinc oxide (sc-ZnO) with a fiber-like shape using a spray-drying process. A colloidal ZnO solution mixed with PVA (pH = 12) was prepared, and sprayed on glass substrates heated at 70 °C to prepare deposition films. The films formed fiber-like strips on the substrate after drying. The fiber-like ZnO films comprised bunches of needle-like objects, which were verified as sc-ZnO along the crystal orientation (101). This study discussed the critical factors for ZnO crystallization, such as PVA additives, and substrate temperature. The mechanism of sc-ZnO formation on the ZnO/PVA interface was described, based on the water evaporation (drying) conditions of the film.

Growth and Z-scan analysis of semi-organic Bis(picolinic acetate) Zinc(II) single crystal for third order NLO applications

Here, we report a new semi-organic single crystal namely Bis(picolinic acetate) Zinc(II) (BPZ) which was grown by a conventional slow evaporation method at room temperature. Structural studies were carried out by single crystal XRD and the results show that Bis(picolinic acetate) Zinc(II) belongs to monoclinic crystal system with space group P21/n. The presence of functional groups in the grown crystal was identified by FTIR spectral analysis. UV-Vis spectral studies reveal that the grown crystals are transparent in the wavelength region of 200-1200 nm. In order to analyze the mechanical strength of the grown crystal, Vickers micro hardness tester was employed. The dielectric properties with respect to different frequency at room temperature were also studied to analyze the dielectric response. The third order nonlinear optical properties were determined by Z-scan studies which shows significant higher values of nonlinear absorption coefficient (β) and third order nonlinear susceptibility (χ3). The enhanced third order nonlinear behavior suggests that the title compound is suitable for nonlinear optical applications.

Density Function Theory calculation, and phthalonitrile process for a synthesis of single crystal zinc phthalocyanine

This study aims to synthesize the β-phase single crystal of zinc phthalocyanine (ZnPc) by using phthalonitrile process and vapor deposition. The single-crystal X-ray diffraction was used to identify the molecular structure and lattice parameters of the synthesized material. The molecular structure, frontier molecular orbitals, and IR spectroscopy of ZnPc were investigated through Time Dependent (TD)-Density Function Theory (DFT) calculations that is compared with experimental results. For the solid-state simulation, the experimental crystallographic data was used to determine band structure and density of state using DFT method on Quantum Espresso. The β-phase monoclinic single crystal of ZnPc is as a direct band gap semiconductor with the calculated energy gap of 2.1 eV, and the Fermi energy level of 2.61 eV.

Diffusion of indium in single crystal zinc oxide: a comparison between group III donors

Dopant diffusion of indium (In) in single crystal zinc oxide is studied by secondary ion mass spectrometry and is interpreted using a reaction–diffusion model that invokes predictions from density functional theory (DFT). An apparent activation energy of 2.2 eV is obtained for the diffusion of In, when the local Fermi-level position is about 0.2 eV below the conduction band edge. The diffusion of In is found to be significantly faster that that reported for the other group III donors, aluminum and gallium, with several orders of magnitude higher effective diffusivities, that can be assigned to a lower migration barrier for the diffusion of In. Furthermore, our results reveal self-consistency in previous DFT results of defect formation- and migration energies. From this, the diffusion of In is suggested to occur through mobile charged zinc vacancies that form intermediate mobile ()− pairs. The pairs in turn dissociate rather readily at the studied temperatures (850 °C–1150 °C), which results in distinct and abrupt diffusion fronts for the In depth distribution profiles.

Exploring Li-ion hopping behavior in zinc ferrite and promoting performance for flexible solid-state supercapacitor

Zinc ferrite as an electrode material for electrochemical energy storage has attracted much attention due to its good pseudocapacitive performance. However, Li-ion diffusion behavior in zinc ferrite has not been clearly understood, therefore, further improvements are still facing challenges. Herein, we report a controlled growth of single crystal mesoporous zinc ferrite (ZnFe2O4) nanowall arrays on highly flexible carbon textile for flexible supercapacitors. Li-ion hopping behavior and energy barrier in ZnFe2O4 are calculated by the density functional theory. The electrode based on the ZnFe2O4 nanowall arrays exhibits high specific capacity of 162.7 mAhg−1 at 3.35 Ag−1 (1170 Fg−1 at 3.35 Ag−1) with excellent capacity retention of 96.4% after 8000 cycles. Furthermore, a flexible symmetric solid-state supercapacitor based on the ZnFe2O4 nanowall arrays is fabricated, which exhibits excellent capacitive performance (620 F g−1 at 5 mVs−1) with high flexibility and super-long life by retaining 97.35% of its initial capacitance after 10000 cycles, and high energy density of 85 Wh kg−1 at power density of 1000 W kg−1. The results indicate that the ZnFe2O4 nanowall arrays is a promising material for the future generation of high-performance supercapacitors. The finding of Li-ion diffusion behavior presents a better understanding of the pseudocapacitive contribution of spinel structured binary metal oxides.

Equations of state in materials beyond the assumption of isotropy of volume compressibility

The process of elastoplastic deformation is considered for materials whose symmetry of elastic properties is modeled by means of five or more independent elastic constants. In the simulation of shock loading of a zinc single crystal characterized by a transversal isotropy of elastic and plastic properties, it was assumed that there is no volume isotropy of compressibility. Different equations of state are applied in a three-dimensional arrangement in the condition of plastic deformation in the direction of each axis. They reflect the relationship of hydrostatic stress to the degree of compression of the material. It is shown that the application of various equations of state changes the propagation velocity of volume waves and introduces a change in the wave pattern of deformation in anisotropic materials.

Enhanced physical properties of potassium zinc sulphate hydrate single crystal following iodide doping

The crystal grown from mixing potassium iodide and zinc sulphate in an aqueous solution was found to be a single crystal potassium zinc sulphate hydrate. The iodide ions enter the crystal matrix as a dopant with small ratio. The evaluation of the crystal structure was achieved by single crystal diffraction and the resolved structure was monoclinic with space group P21/c. The effect of iodide doping is observed in the crystal morphology and the x-ray powder diffraction pattern. The iodide ions were detected in the grown crystal using x-ray fluorescence and energy dispersive x-ray which spotted a very small fraction of iodide in the raw materials of the crystal. The iodide doping also affected the thermal stability of the original crystal and introduced different thermal behavior. The optical properties are also affected and a noticeable band in the transmittance is observed. The iodide effect on the structure of optical energy gap is analyzed using photoluminescence spectra. Second harmonic generation test shows an unexpected behavior based on the structure of the grown crystal.

Deformation Behavior of Pure Zinc Single Crystals during a single pass of ECAP

A single pass of equal channel angular pressing (ECAP) at 223 K was applied to six kinds of Zn bulk single crystals with different crystal orientations, and the deformation behavior was investigated, such as grain refinement and texture development. Zn bulk single crystals with several millimeters can be divided into a number of grains with several tens micron meters by a single pass of ECAP. Also, texture formed by activation of basal and second order pyramidal slips. Increasing twin boundaries by double twinning, and occurrences of recrystallization at the twin boundaries are required for grain refinement before passing through the theoretical shear plane in the ECAP die.