Direction Of Crystal Axis Research Articles

Effect of Grain Size on the Uniaxial Compressive Strength of Ice Forming with Different Wind Speeds in a Cold Laboratory

This study investigated the uniaxial compressive strength of distilled water ice prepared in a low-temperature laboratory at −30 °C at varying wind speeds of 0 m/s, 1 m/s, 2 m/s, 4 m/s, 6 m/s, and 8 m/s. The crystal structure and grain size of the ice were measured. The results indicated that, during the ice forming period, the higher the wind speed, the lower the grain size. Uniaxial compression tests were conducted parallel to the ice crystal long axis direction within a strain rate range of 10−6 s−1 to 10−2 s−1. The experimental temperature was controlled at −10 °C. Stress–strain curves were generated, elucidating the mechanical properties and failure modes of the ice. The results suggest that the uniaxial compressive strength of ice is related to the strain rate by a power–law function and shows a linear correlation with −1/2 power of grain size. The results explain the physical fact that the strength of ice is higher when the ice is formed in low-temperature and high-wind-speed environments. Additionally, this highlights how wind speed influences ice strength by controlling grain size during ice forming.

Effect of polarization electric field in photodegradation over ε-Cd(IO3)2 photocatalyst against antibiotics and dyes

The efficient photogenerated carriers separation is the key factor in enhancing the activity of photocatalysts to solve environmental pollution problems. The internal polarized electric fields in polar materials most likely provide a more direct and stronger driving force for photogenerated carriers separation. Here, we investigate polar ε-Cd(IO3)2 (CIO) with two different morphologies as an efficient photocatalyst for the photodegradation of antibiotics and dyes. According to the theoretical calculation of the ratios of mh*/me* along three different crystal axis directions, the photogenerated carrier separation efficiency along the c-axis direction is the largest, which matches the direction of the polarized electric field in the crystal. The internal polarized electric field promotes the separation of photogenerated carriers, leading to a high transfer efficiency of the catalyst. Moreover, photodegradation experiments demonstrate that the photocatalytic activity of CIO-1 is approximately 3 times that of TiO2 P25. This study provides some insights that might aid the development of polar photocatalysts with superior performance.

Modeling of Creep Deformation Behavior of DZ411 and Finite Element Simulation of Turbine Blade

Creep tests were conducted on DZ411 material at 930 °C and 850 °C, and creep curves were recorded and employed in normalization creep model building. A yield function suitable for directional solidification nickel-based materials was proposed in an ascending-order approach. Combined with the normalized creep model and the proposed function, a creep subroutine was compiled to simulate the creep deformation behavior of a turbine blade. The typical boundary conditions of the blade were determined and used for finite element analysis. According to the analysis results, the assessment positions for the actual application of a turbine blade were determined and checked for endurance intensity. The phenomenon of deviation angle between crystal axis and blade height direction in actual casting was further analyzed. Multiple angles and directional deviation angles were simulated for 10,000 h creep deformation. Considering the difficulties and challenges of the complex geometric structures of blades, it is necessary to conduct creep tests of DZ411 material and a simulation analysis of a real blade. Based on the above analysis and discussion, the present work sheds light on finite element analysis and has great potential for structural analyses in the engineering applications of complex high-temperature structures.

Full-aperture random polarization smoothing for a low-coherence laser facility.

Two new random polarization smoothing methods using full-aperture elements are proposed on low-coherence lasers, one using birefringent wedge and one using flat birefringent plate. By designing the crystal axis direction and wedge angle of the birefringent plates, the methods can selectively introduce time delay and spatial displacement, so as to obtain fast random evolution of transient polarization by utilizing low spatiotemporal coherence of the laser focal field. Both methods avoid the near field discontinuity and can be used under high fluence. The method using birefringent wedge can slightly improve focal spot uniformity, and the method using flat birefringent plate can obtain non-polarization with DOP lower than 2%. Theoretical studies show that the resulting focal polarization evolves rapidly on sub-picosecond timescales and rapidly covers the entire Poincaré sphere. The method using birefringent wedge is achieved in experiment. The results show that the degree of polarization of the focal spot is reduced from 1 to 0.27, which proves the effectiveness of the full-aperture random polarization smoothing. The full-aperture random polarization smoothing can generate a focal field very close to unpolarized thermal light, which is expected to suppress the laser plasmas instability.

A three-phase volume-averaged solidification model considering the growth direction of columnar crystal axis

The volume-averaged solidification model has generated considerable research interest in metallurgical areas. The model is complicated but flexible to address many problems faced. However, few previous studies focused on the role of the growth direction of the columnar crystal axis in this model. The current work aims to integrate the columnar growing direction into the volume-averaged solidification model. An optimized algorithm for updating the average length of columnar tips is proposed based on the columnar growing direction. The numerical model was verified by a benchmark experiment of directional solidification. Simulation results agreed well with experimental results, including temperature fields, macrosegregation, macrostructure, and the columnar growing direction. Results showed that the optimized columnar-tip tracking algorithm had some effects on the advancement of the columnar front during initial solidification. The overestimation of the columnar length caused an overestimation of the columnar front. Although the final simulated results did not show a great difference after the optimization, these finds were significant in at least three major respects. First, the columnar crystal growing direction in an ingot could be obtained. The columnar growing direction is also a quality parameter of an ingot. Second, the algorithm for updating the average length of columnar tips made more sense in theory. Third, the optimization could provide a more reliable result during initial solidification. The optimized method is worth developing in the future volume-averaged solidification model.

In situ synthesis and photocatalytic hydrogen production of plate‐like Cu‐doped TiO 2 polycrystal with crystal‐axis orientation

The Cu-doped TiO2 plate-like particle was synthesised via using the layered H1.07Ti1.73O4·H2O (HTO) plate-like particle as a precursor. The Cu-doped TiO2 particle consists of nanocrystals and holes, and these nanocrystals are oriented at [ 1 ¯ 1 ¯ 1 ]-crystal-axis direction. Firstly, the HTO particle was treated in a copper acetate solution, forming Cu2+-exchanged HTO plate-like particles. And then Cu2+-exchanged HTO in situ transformed into Cu-doped TiO2 via heat-treating and further acid washing. The Cu-doped TiO2 particle has a stronger absorption in the visible light region of 400–800 nm and the visible photocatalytic H2 production activity.

Thermal bistability of magnon in yttrium iron garnet microspheres

In this work, the thermal bistability of magnons in yttrium iron garnet microspheres was experimentally characterized. Using high quality factor optical whispering gallery modes in the microsphere, the temperature change caused by the microwave pump is precisely measured by probing the optical resonance wavelength shift. It is found that temperature change also induces the magnonic frequency shift and the frequency shift depends on the crystal axis direction of the material. With some appropriate alignment of the magnetic field and the microsphere, the magnonic frequency shift induced by the thermal bistability from the microwave can be suppressed. Our results show its potential use in future experiments on magnon-based transducers.

層状チタン酸テンプレートを用いた反応性テンプレート粒子成長法によるBa<sub>1−x</sub>Ca<sub>x</sub>TiO<sub>3</sub>配向性セラミックスの作製

Piezoelectric performance can be improved by using crystal-axis oriented materials because piezoelectric properties of the ferroelectric materials are dependent on the crystal-axis direction. In this study, we tried to fabricate Ba1−xCaxTiO3 (BCT) oriented ceramics by reactive template grain growth (RTGG) method using H1.07Ti1.73O4 layered titanate (HTO) plate-like particles as the reactive template. BCT ceramics with [110]-orientation were prepared using HTO-BaCO3-Ca(OH)2 (HBC) and HTO-BaCO3-Ca(OH)2-TiO2 (HBCT) reaction systems. The degree of orientation and the relative density of the BCT ceramics are dependent on the green sheet preparation conditions, such as dispersion condition and added binder amount, calcination temperature and starting material composition. In these reaction systems, firstly oriented BCT particles are formed by a topotactic reaction of HTO template particles with Ba and Ca matrix components, and then, BCT oriented ceramic is formed by the growth of the oriented BCT particles. BCT ceramics with higher density and higher orientation can be fabricated using HBCT reaction system than HBC reaction system, where the orientation degree is dependent strongly on the ratio of HTO template particle to TiO2 matrix particle.

Measurement of refractive indices of GdTaO4 crystal by the auto-collimation method

In this paper, the refractive index of GdTaO4 crystal is measured by the auto-collimation method. GdTaO4 crystal is processed into three rectangular prisms, their planes with longer right angle side are planes a, b and c of the crystal, respectively, and their normal directions are the directions of crystal plane axes a, b and c, respectively. with a side by angle . Plane enclosed by hypotenuse and the longer right angle side is subjected to fine polishing, while the surface plating for the latter is subjected to Al reflectance coating, so that the light is incident along the hypotenuse plane with minimum angle of deviation (), reflects on the plane with longer right angle and returns along the original path. The rectangular prisms processed by GdTaO4 crystal are placed on the platform of 32 J goniometer with an accuracy of arc seconds. The 473, 532 nm YAG double frequency laser, 633 nm He-Ne laser and 1064 nm YAG laser with stable light intensity are used as a measuring light source, light will refract into the light perpendicular to the longer right angle side when the laser of measuring light source shoots towards the bevel of a prism with a minimum angle of deviation (). The refractive indexes nx, ny, and nz of a crystallographic axis directions can be measured by , and the relationship between refractive index ellipsoid section and prism refraction of light. The constants Ai, Bi, Ci, and Di (i=x, y, z) are given in Sellmeier's equation ni2 =Ai+Bi/(2-Ci)-Di2, and the values of angle Vz included between light axis and refractive index at wavelengths of 473, 532, 632.8 and 1064 nm are calculated to be 22.5, 22.5, 21.9 and 22.0, respectively. It is proved that GdTaO4 crystal is optically positive biaxial crystal.

Theoretical study on the electron transport properties of chlorinated pentacene derivatives

The effects of chlorination on the geometries, electronic structures and transport properties for some chlorinated pentacene derivatives (nCl-PENT-n) have been theoretically investigated by using density functional theory calculations and Marcus-Hush theory. Compared with PF-PENT, introducing chlorine atoms into pentacene, remarkably decreases the frontier molecular orbital energies while scarcely increases the internal reorganization energy, therefore improves their air-stability and ability of electron injection. Based on the experimental crystal parameters, the predicted hole and electron mobility (μh=0.46cm2V−1s−1, μe=0.61cm2V−1s−1) values for 6,13-dichloropentacene (DCP) crystal indicate that DCP crystal may be a promising candidate as ambipolar OFET materials. After the present work the results indicate that 4Cl-PENT-1 should be good n-channel material (μe=2.74cm2V−1s−1). In addition, the angular dependent simulation for electron mobility shows that the electron transport is remarkably anisotropic in the studied molecular crystals and the maximum μe appears along the crystal axis direction since molecules along this direction exhibit the close face-to-face stacking arrangement with short interplanar distances (∼3.7–5.3Å), which induces large electronic couplings.

Invited; Growth of Czochralski Silicon Crystals with Ultralow Carbon Concentrations for High-Power Insulated-Gate Bipolar Transistor Devices

Introduction To achieve lower ON-resistances in insulated-gate bipolar transistor (IGBT) devices, silicon crystals should exhibit long carrier lifetimes. Generally, floating-zone (FZ) silicon exhibits longer carrier lifetimes than magnetic-field-induced Czochralski (MCZ) silicon, and therefore, it is used in high-power IGBT devices. However, since FZ silicon has lower productivity than MCZ silicon, development of high-quality MCZ silicon with long carrier lifetimes is crucial for supporting the growing demand for IGBT devices. To this end, we focused on reducing carbon impurities in MCZ silicon, because these impurities act as heterogeneous nucleation sites for oxygen precipitates and consequently shorten carrier lifetime. Carbon with concentrations lower than 1015 atoms/cm3, which is the detection limit of FT-IR, was evaluated by photoluminescence (PL) spectroscopy. Carbon can be detected in silicon crystals at lower concentrations of the order of 1013 atoms/cm3 by using the quantitative relationship between the carbon concentration and the PL intensity of carbon complexes generated by electron irradiation [1]. Growth of CZ silicon crystals with ultralow carbon concentrations During CZ growth, carbon contamination is mainly influenced by the back-diffusion of carbon monoxide (CO) into the melt; here, CO is generated by the reaction between silicon monoxide (SiO) and the graphite parts. Moreover, the starting polycrystalline silicon contains carbon impurities in concentrations of ~5×1014 atoms/cm3. Therefore, to reduce carbon concentration in CZ silicon below that in FZ silicon, CO back-diffusion and the carbon impurities originating from the starting polycrystalline silicon both need to be reduced. Fig. 1 shows the dependence of carbon concentrations in 6-inch CZ silicon on the solidified fraction [2]. During growth in the conventional hot zone, the carbon concentration in CZ silicon was higher than that in FZ silicon because of CO back-diffusion (Fig. 1a). In this study, CO back-diffusion was prevented by using a hot zone that can reduce the reaction between SiO and the graphite parts such as the heater. Because the carbon distribution in the crystal growth axis direction was similar to that predicted by the effective segregation law, it was confirmed that CO incorporation into the melt was almost prevented during the growth processes (Fig. 1b). Furthermore, upon increasing the argon (Ar) flow rate, carbon concentrations decreased gradually for solidified fractions lower than 30% (Fig. 1c). This indicates that CO evaporation from the melt dominated over CO incorporation into the melt. By promoting CO evaporation, we managed to grow 6-inch CZ silicon crystals with a carbon concentration lower than 1.0×1014 atoms/cm3. Acknowledgments This work was partly supported by the New Energy and Industrial Technology Development Organization (NEDO) under the Ministry of Economy, Trade and Industry (METI) of Japan.

Theoretical investigation on the crystal structures and electron transport properties of several nitrogen-rich pentacene derivatives

Exploring and synthesizing new simple n-channel organic semiconductor materials with large electron mobility and high air stability have remained a major challenge and hot issue in the field of organic electronics. In the current work, the electron transport properties of four novel nitrogen-rich pentacene derivatives (PBD1, PBD2, PBD3, and PBD4) with two cyano groups as potential n-channel OFET materials have been investigated at the molecular and crystal levels by means of density functional theory (DFT) calculations coupled with the prediction of crystal structures and the incoherent charge-hopping model. Calculations reveal that the studied compounds, which possess low-lying frontier molecular energy levels, large ionization potentials and electron affinities, are very stable exposed to air. Based on predicted crystal structures, the average electron mobility at room temperature (T = 300 K) for PBD1, PBD2, PBD3, and PBD4 is predicted to be as high as 0.950, 0.558, 0.518, and 1.052 cm²·V⁻¹·s⁻¹, which indicate that these four compounds are more than likely to be promising candidates as n-type OFET materials under favorable device conditions. However, this claim needs experimental verification. In addition, the angular-dependent simulation for electron mobility shows that the electron transport is remarkably anisotropic in these molecular crystals and the maximum μ(e) appears along the crystal axis direction since molecules along this direction exhibit the close face-to-face stacking arrangement with short interplanar distances (~3.6-4.0 Å), which induces large electronic couplings.

Beta tricalcium phosphate ceramics with controlled crystal orientation fabricated by application of external magnetic field during the slip casting process

Beta tricalcium phosphate (β-TCP) is a resorbable bioceramic that has hitherto been utilized in the medical field. Since it crystallizes in the anisotropic hexagonal system, properties such as chemical and physical ones are expected to depend on its crystal axis direction and/or on its crystal plane (anisotropy). Control of crystal orientation is thus important when used in polycrystalline form. Meanwhile, application of a strong magnetic field has been found to be a promising technique to control crystal orientation of anisotropic shape or structured crystals. In this work, we attempted to fabricate β-TCP ceramics with controlled crystal orientation by applying an external magnetic field during the slip casting process and subsequently sintering them at 1050°C, below the β–α transition temperature. Application of a vertical magnetic field increased intensities of planes perpendicular to c-plane on the top surface, while a horizontal one with simultaneous mechanical mold rotation decreased it. These results indicated that crystal orientation of β-TCP ceramics were successfully controlled by the external magnetic field and together that the magnetic susceptibility of β-TCP is χc⊥>χc//.

Магнитоэлектрический эффект и типы магнитного упорядочения в пленках мультиферроиков

Space – modulated structures of cycloidal type in a (111) – oriented bismuth ferrite type multiferroic films have been investigated. It has been shown that spin cycloids with a definite direction of propagation vector are realized in the films which is connected with the presence of surface magnetic anisotropy attributed to magnetoelastic interactions. The influence of magnetic field applied in principal crystal axis direction on the character of magnetic ordering in multiferroic films has been considered. The boundaries of transition of space – modulated structure into homogeneous magnetic state has been determined.

Upper critical field of p-wave ferromagnetic superconductors with orthorhombic symmetry

We extended the Scharnberg-Klemm theory of Hc2(T) in p-wave superconductors with broken symmetry to cases of partially broken symmetry in an orthorhombic crystal, as is appropriate for the more exotic ferromagnetic superconductor UCoGe in strong magnetic fields. For some partially broken symmetry cases, Hc2(T) can mimic upward curvature in two crystal axis directions, and reasonably good fits to some of the UCoGe data are obtained.

Symmetry of the Hidden Order in URu2Si2from Nuclear Magnetic Resonance Studies

The hidden order (HO) in URu 2 Si 2 has been investigated by both 29 Si and 99 Ru NMR on a single crystal. Tiny, but finite additional broadening of the spectrum in the HO phase in both 29 Si and 99 Ru NMR with external magnetic field applied along the crystallographic [100] or [110] direction, and its persistence as H ext →0 in 29 Si NMR clearly indicate the existence of internal hyperfine field, and the breaking of the time-reversal symmetry in the HO phase can therefore be concluded. We discuss which symmetry of the D 4 h symmetry group of the URu 2 Si 2 crystal structure is compatible with the observed dependence on the crystal-axis direction of the existence or nonexistence of the internal hyperfine field. Then, by imposing a strong constraint that the wave-vector of the HO is also Q 0 =[0,0,1], the wave-vector of the pressure-induced antiferromagnetism, we show that the two-dimensional representation E - remains as the only possible candidate for the HO symmetry. Since dipoles are obviously excluded...

Micro Cutting of Sapphire

Sapphire has high mechanical strength at high temperatures and high pressure. Thus, micro devices made of sapphire are expected to be used in extreme environments such as aerospace, defense and marine. Then, the machining technology is required for manufacturing of 3 dimensional shapes. The paper discusses the micro cutting process of sapphire to determine the applicable cutting parameters in planing and milling. First, the critical stress at which crack initiation occurs is measured in the indentation test with detecting AE signal. The critical stress of sapphire is beyond 22.6 GPa, which is much higher than those of glasses. Then, the critical depths of cut, maximum depths of cut in which crack-free surfaces were finished, were measured in cutting of r crystal plane. The critical depth of cut is maximized when the cutting is performed in a crystal axis direction. In milling of sapphire, adhesion of chip onto the surface finish should be considered as well as brittle fracture. In milling of r crystal plane, the surface finish is improved better than those of the other crystal planes. Adhesion of material can also be controlled by supplying lubrication.

Effect of dimensionality crossover on magnetovolume properties of quasi one-dimensional weakly antiferromagnetic metals

Magnetic properties and thermal expansion of quasi one-dimensional itinerant electron magnets close to the antiferromagnetic instability are studied. By controlling the relative spectral dispersions of spin fluctuation spectra depending on the direction of crystal axes, we show that the three dimensional properties are changed with increasing the one-dimensional anisotropy. Crossover behaviors are discussed on the temperature dependence of the magnetic susceptibility and the magnetovolume expansion around their critical regions.

Ultrastructural Observation of Hydroxyapatite Ceramics with Preferred Orientation to a-plane Using High-resolution Transmission Electron Microscopy

The dense hydroxyapatite (HAp) ceramics with preferred orientation to a-plane were fabricated using composite powders of single-crystal apatite fibers (AF) and wet-synthesized apatite gels (AG). AF was synthesized by homogeneous precipitation method. The composites of AF and AG were prepared as the following process. Aqueous (NH4)2HPO4 solutions were added into the AF slurry with the amount of 1 mass%. In addition, aqueous Ca(NO3)2 solutions were added dropwise to the slurry to precipitate the AG on the AF at room temperature, and then aged at room temperature for 24h with stirring. The dried powders were uniaxially pressed at 200MPa of compaction pressure and then fired at 1300 ¼C for 5h. All the resulting ceramics were identified with HAp single phases. The (100), (200) and (300) reflections which correspond to a-plane were more intense than those of a standard HAp ceramics. With increasing the additive amount of AG, the orientation degree of a-plane decreased, and the relative density increased. Furthermore, the ultrastructure of the resulting ceramics was examined by high-resolution transmission electron microscopy. The selected area electron diffraction patterns showed clear spots corresponding to [110] zone axis direction of HAp crystal with high crystallinity. The lattice spacings of crystal grains were determined to be 0.34nm or 0.68nm which corresponds to the lattice constant of (002) or (001) plane of HAp crystal. Therefore, the resulting ceramics were HAp single phases with preferred orientation to a-plane.

Stoichiometry Dependence of Li+ Diffusivity in LiNbO3 Crystal in Off‐Congruent, Li‐Deficient Regime

Diffusivity at 1130°C of Li+ in LiNbO3 crystal in off‐congruent, Li‐deficient regime has been studied as a function of Li2O‐content. A diffusion‐limited Li2O‐content reduction depth profile in an X‐ or Z‐cut plate, ranging from 47.2 to 48.5 mol%, was produced by carrying out Li‐poor vapor transport equilibration (VTE) treatment on 1‐mm‐thick, initially congruent plates at 1130°C for 150 h. The profile was obtained by alternatively doing the optical polish to one crystal surface and the Li2O‐content characterization on the polished surface through the measurement on birefringence. The Boltzmann–Matano mathematical analysis was applied to the profile to obtain the Li2O‐content dependence of Li+ diffusivity. The results show that the diffusivity decreases with the decreased Li2O‐content and the decrease is by at least one order of magnitude as the Li2O‐content decreases by 1 mol% from 48.5 mol%. The diffusion shows slight anisotropy and is faster along the optical axis direction of crystal. In combination with previously reported result in the near‐stoichiometric regime, the diffusivity over the Li2O‐content range from 47 to 50 mol% is presented.