High Degree Of Preferred Orientation Research Articles

Influence of Hardwood Lignin Blending on the Electrical and Mechanical Properties of Cellulose Based Carbon Fibers.

Carbon fibers (CFs) are fabricated by blending hardwood kraft lignin (HKL) and cellulose. Various compositions of HKL and cellulose in blended solutions are air-gap spun in 1-ethyl-3-methylimidazolium acetate (EMIM OAc), resulting in the production of virtually bead-free quality fibers. The synthesized HKL-cellulose fibers are thermostabilized and carbonized to achieve CFs, and consequently their electrical and mechanical properties are evaluated. Remarkably, fibers with the highest lignin content (65%) exhibited an electrical conductivity of approximately 42 S/cm, surpassing that of cellulose (approximately 15 S/cm). Moreover, the same fibers demonstrated significantly improved tensile strength (∼312 MPa), showcasing a 5-fold increase compared to pure cellulose while maintaining lower stiffness. Comprehensive analyses, including Auger electron spectroscopy and wide-angle X-ray scattering, show a heterogeneous skin-core morphology in the fibers revealing a higher degree of preferred orientation of carbon components in the skin compared to the core. The incorporation of lignin in CFs leads to increased graphitization, enhanced tensile strength, and a unique skin-core structure, where the skin's graphitized cellulose and lignin contribute stiffness, while the predominantly lignin-rich core enhances carbon content, electrical conductivity, and strength.

Solvent and A-Site Cation Control Preferred Crystallographic Orientation in Bromine-Based Perovskite Thin Films.

Preferred crystallographic orientation in polycrystalline films is desirable for efficient charge carrier transport in metal halide perovskites and semiconductors. However, the mechanisms that determine the preferred orientation of halide perovskites are still not well understood. In this work, we investigate crystallographic orientation in lead bromide perovskites. We show that the solvent of the precursor solution and organic A-site cation strongly affect the preferred orientation of the deposited perovskite thin films. Specifically, we show that the solvent, dimethylsulfoxide, influences the early stages of crystallization and induces preferred orientation in the deposited films by preventing colloidal particle interactions. Additionally, the methylammonium A-site cation induces a higher degree of preferred orientation than the formamidinium counterpart. We use density functional theory to show that the lower surface energy of the (100) plane facets in methylammonium-based perovskites, compared to the (110) planes, is the reason for the higher degree of preferred orientation. In contrast, the surface energy of the (100) and (110) facets is similar for formamidinium-based perovskites, leading to lower degree of preferred orientation. Furthermore, we show that different A-site cations do not significantly affect ion diffusion in bromine-based perovskite solar cells but impact ion density and accumulation, leading to increased hysteresis. Our work highlights the interplay between the solvent and organic A-site cation which determine crystallographic orientation and plays a critical role in the electronic properties and ionic migration of solar cells.

Preferred orientation in polycrystalline colossal electroresistive hollandite PbFexV6‐xO11

AbstractPreferred orientation in polycrystalline materials is one of the most challenging problems for structural analysis. Significant preferred orientation can severely affect the structure‐property analysis of the systems having substantial crystallographic anisotropy. Here, an extremely high degree of preferred orientation has been demonstrated in R‐block hollandite hexagonal PbFexV6−xO11 compounds, which has recently been shown to exhibit an unusual colossal electroresistance response that has a strong dependence on structural modifications. The present results warn against possible errors in understanding the evolution of the crystal structure of these hollandites, which might adversely affect the estimation of the influence of the same on their spectacular physical properties.

Tailoring Preferential Orientation in BaTiO3‐based Thin Films from Aqueous Chemical Solution Deposition

AbstractFerroelectric properties of thin films can be enhanced by crystallographic texture. In this work, we report on how heat treatment of films can be designed to tailor the degree of preferential orientation in BaTiO3‐based thin films from aqueous chemical solution deposition. In situ synchrotron X‐ray diffraction in combination with Rietveld refinements was used to study the crystallization process of films from a single deposition and to give an in‐depth characterization of the crystallographic texture of the films. Transmission electron microscopy was employed to evaluate the microstructure and degree of preferred orientation in thicker films from multiple depositions. Texture was induced in the multilayer films by a repeated annealing process. Cube‐on‐cube growth was demonstrated to occur in both single and multi‐layered films provided the heating program was designed to give limited nucleation and growth below the threshold for where cube‐on‐cube growth is favoured, resulting in a very high degree of preferred orientation. The cube‐on‐cube grown films were relaxed with respect to the lattice unit cell mismatch between the film and the substrate, where the relaxation of stress depends on the film thickness. Texture and cube‐on‐cube growth were demonstrated on several types of single‐crystal oxide substrates. Calcium and zirconium substitution did not alter the crystallization process, but zirconium slowed down the texture formation kinetics. The ferroelectric response was strongest in the films with a high degree of preferred orientation.

The effect of the spinning conditions on the structure of mesophase pitch-based carbon fibers by Taguchi method

Taguchi’s experimental design was employed in the melt spinning of molten mesophase pitch to produce carbon fibers. The textures of the obtained carbon fibers were radial with varied crack angles, as observed by scanning electron microscopy and polarized optical imaging. The diameter, crack angle, preferred orientation, and tensile modulus of the produced samples were examined to investigate the influence of four spinning variables. The relative importance of the variables has been emphasized for each characteristic. The results show that thicker carbon fiber can be obtained with a smaller entry angle, a higher spinning temperature, a reduced winding speed, and an increased extrusion pressure. The winding speed was found to be the most significant factor in relation to the fiber diameter. While it was observed that thicker carbon fiber generally shows improved preferred orientation, the most important variable affecting the preferred orientation was found to be the entry angle. As the entry angle decreased from 120° to 60°, the shear flow was enhanced to induce more ordered radial alignment of crystallite planes so as to obtain carbon fibers with a higher degree of preferred orientation. As a consequence, the crack angle was increased, and the tensile modulus was improved.

Influence of fibre distribution and orientation on the flexural behaviour of beams cast from flowable hybrid polymer–steel FRC

The present study analyses the performance of full-scale beams cast from flowable hybrid polymer FRC with regard to fibre distribution and orientation. To identify possible flow-induced effects, variations of the fibre contents and orientation factors were investigated along the length and over the height of the beams. The study includes a comparison of the fibre distribution and orientation between standard specimens and full-scale beams, and the influence thereof on flexural behaviour and design assumptions. For the full-scale beams, it is found that fibres, even combined, distribute differently by type: steel fibres tend to segregate after a certain flow length, while polymer fibres distribute evenly. Furthermore, polymer fibres seem to adopt a higher degree of preferred orientation, especially in the bottom half of the beams. This research confirms that the modelling of the full-scale beams on the basis of results from standard specimens leads to an overestimation of their flexural response. However, the present study demonstrates how such overestimation can be considerably reduced if the tensile response from standard tests is adjusted to account for variations in the fibre content and orientation.

X-Ray Diffraction Computed Tomography for Structural Analysis of Electrode Materials in Batteries

We report the use of X-ray diffraction in combination with computed tomography to provide quantitative information of a coin cell Li-ion battery and a commercial Ni/MH AAA battery for the first time. This technique allows for structural information to be garnered and opens up the possibility of tracking nanostructural changes in operandi. In the case of the cylindrically wound, standard AAA Ni/MH cell, we were able to map all the different phases in the complex geometry, including anode, cathode, current collector and casing, as well as amorphous phases such as the binder and separator. In the case of a Li-ion coin cell battery, we show how the X-ray diffraction tomography data can be used to map crystal texture of the LiCoO2 particles over the cathode film. Our results reveal that the LiCoO2 microparticles show a high degree of preferred orientation, but that this effect is not homogenous over the film, which may affect the electrochemical properties.

Linking preferred orientations to elastic anisotropy in Muderong Shale, Australia

The significance of shales for unconventional hydrocarbon reservoirs, nuclear waste repositories, and geologic carbon storage has opened new research frontiers in geophysics. Among many of its unique physical properties, elastic anisotropy had long been investigated by experimental and computational approaches. Here, we calculated elastic properties of Cretaceous Muderong Shale from Australia with a self-consistent averaging method based on microstructural information. The volume fraction and crystallographic preferred orientation distributions of constituent minerals were based on synchrotron x-ray diffraction experiments. Aspect ratios of minerals and pores, determined from scanning electron microscopy, were introduced in the self-consistent averaging. Our analysis suggested that phyllosilicates (i.e., illite-mica, illite-smectite, kaolinite, and chlorite) were dominant with [Formula: see text]. The shape of clay platelets displayed an average aspect ratio of 0.05. These platelets were aligned parallel to the bedding plane with a high degree of preferred orientation. The estimated porosity at ambient pressure was [Formula: see text] and was divided into equiaxial pores and flat pores with an average aspect ratio of 0.01. Our model gave results that compared satisfactorily with values derived from ultrasonic velocity measurements, confirming the validity and reliability of our approximations and averaging approach.

Phase and Texture Evolution in Chemically Derived PZT Thin Films on Pt Substrates

The crystallization of lead zirconate titanate (PZT) thin films was evaluated on two different platinum‐coated Si substrates. One substrate consisted of a Pt coating on a Ti adhesion layer, whereas the other consisted of a Pt coating on a TiO2 adhesion layer. The Pt deposited on TiO2 exhibited a higher degree of preferred orientation than the Pt deposited on Ti (as measured by the Full Width at Half Maximum of the 111 peak about the sample normal). PZT thin films with a nominal Zr/Ti ratio of 52/48 were deposited on the substrates using the inverted mixing order (IMO) route. Phase and texture evolution of the thin films were monitored during crystallization using in situ X‐ray diffraction at a synchrotron source. The intensity of the Pt3Pb phase indicated that deposition on a highly oriented Pt/TiO2 substrate resulted in less diffusion of Pb into the substrate relative to films deposited on Pt/Ti. There was also no evidence of the pyrochlore phase influencing texture evolution. The results suggest that PZT nucleates directly on Pt, which explains the observation of a more highly oriented 111 texture of PZT on the Pt/TiO2 substrate than on the Pt/Ti substrate.

Temperature dependence on p-Cu2O thin film electrochemically deposited onto copper substrate

In this study, we attempted to quantitatively interpret the effect of electrodeposition temperature on Cu2O film's microstructure, optical and photoelectrochemical properties. Three deposit temperatures (35, 50 and 65°C) were taken into consideration. Based upon our observations, a general trend was concluded. That is, Cu2O films deposited at lower temperature (35°C) always possessed a high degree of preferential orientation, smaller pyramidal-like crystal size, high photolumminance and a higher carrier concentration. These properties made Cu2O films deposited at 35°C a better photoelectrochemical performance with photocurrent density of −0.22mA/cm2 bias −0.4V vs. SCE. This value is about 35% higher than those Cu2O films deposited at higher temperatures. Observed higher photocurrent density is likely due to the intrinsic of a higher charge carrier concentration, and a lower resistance within Cu2O crystal and at Cu2O/electrolyte interface.

Pulsed laser deposition of BiFeO3 thin films with large polarization on Pt(111)/Ti/SiO2/Si by controlling substrate temperature

Bismuth ferrite (BiFeO3) thin films with large polarization were grown on Pt(111)/Ti/SiO2/Si by optimizing the substrate temperatures (T sub). The BiFeO3 thin films were prepared by pulsed laser deposition and the effects of T sub (T sub = 853–913 K) on crystallization orientation, surface morphology and properties of the films were investigated. The microstructure and morphology of the films showed a strong dependence on T sub. The film prepared at T sub = 893 K had a relatively high degree of (111) preferential orientation and densely packed morphology. A large polarization with the maximum remanent polarization of 108 μC/cm2 was obtained, which was due to the high degree of preferential orientation and the dense surface morphology at the optimum substrate temperature.

Effect of Oxide Buffer Layer on the Thermochromic Properties of VO2 Thin Films

VO2 thin films were deposited on soda lime glass substrates with ZnO, TiO2, SnO2, and CeO2 thin films applied as buffer layers between the VO2 films and the substrates in order to investigate the effect of buffer layer on the formation and the thermochromic properties of VO2 film. Buffer layers with thicknesses over 50 nm were found to affect the formation of VO2 film, which was confirmed by XRD spectra. By using ZnO, TiO2, and SnO2 buffer layers, monoclinic VO2 (VO2(M)) film was successfully fabricated on soda lime glass at 370 °C. On the contrary, films of VO2(B), which is known to have no phase transition near room temperature, were formed rather than VO2(M) when the film was deposited on CeO2 buffer layer at the same film deposition temperature. The excellent thermochromic properties of the films deposited on ZnO, TiO2, and SnO2 buffer layers were confirmed from the temperature dependence of electrical resistivity from room temperature to 80 °C. Especially, due to the tendency of ZnO thin film to grow with a high degree of preferred orientation on soda lime glass at low temperature, the VO2 film deposited on ZnO buffer layer exhibits the best thermochromic properties compared to those on other buffer layer materials used in this study. These results suggest that deposition of VO2 films on soda lime glass at low temperature with excellent thermochromic properties can be achieved by considering the buffer layer material having structural similarity with VO2. Moreover, the degree of crystallization of buffer layer is also related with that of VO2 film, and thus ZnO can be one of the most effective buffer layer materials.

Laminar iridium coating produced by pulse current electrodeposition from chloride molten salt

Due to the unique physical and chemical properties, Iridium (Ir) is one of the most promising oxidation-resistant coatings for refractory materials above 1800°C in aerospace field. However, the Ir coatings prepared by traditional methods are composed of columnar grains throughout the coating thickness. The columnar structure of the coating is considered to do harm to its oxidation resistance. The laminar Ir coating is expected to have a better high-temperature oxidation resistance than the columnar Ir coating does. The pulse current electrodeposition, with three independent parameters: average current density (Jm), duty cycle (R) and pulse frequency (f), is considered to be a promising method to fabricate layered Ir coating. In this study, laminar Ir coatings were prepared by pulse current electrodeposition in chloride molten salt. The morphology, roughness and texture of the coatings were determined by scanning electron microscope (SEM), profilometer and X-ray diffraction (XRD), respectively. The results showed that the laminar Ir coatings were composed of a nucleation layer with columnar structure and a growth layer with laminar structure. The top surfaces of the laminar Ir coatings consisted of cauliflower-like aggregates containing many fine grains, which were separated by deep grooves. The laminar Ir coating produced at the deposition condition of 20mA/cm2 (Jm), 10% (R) and 6Hz (f) was quite smooth (Ra 1.01±0.09μm) with extremely high degree of preferred orientation of 〈111〉, and its laminar structure was well developed with clear boundaries and uniform thickness of sub-layers.

Direct Synthesis of Anatase Films with ∼100% (001) Facets and [001] Preferred Orientation

Anatase films exhibiting ~100% (001) reactive facets at the surface were grown hydrothermally on gold substrate from a homogeneous solution of TiF(4) and NaF. In addition to NaF, it was found that TiO(2) films with very similar properties could be prepared with the fluoride salts LiF, CsF, HF, NH(4)F, and N(CH(2)CH(3))(4)F. The polycrystalline anatase films are continuous, approximately 1 μm thick, and evenly coat the substrate. The surface grain size is ~400 nm. Grazing angle XRD measurements show that the films exhibit a high degree of preferred orientation with the c-axis normal to the substrate surface. SEM images reveal that the grains span the thickness of the films. Annealing the films at 500 °C removes fluorine and causes crystallites within the grains to restructure as shown by SEM, XRD, and Raman spectroscopy. Supported anatase films grown from this one-pot method may serve as oxidative photocatalysts and electrodes for photoelectrochemical applications such as solar cells and hydrogen evolution.

Dependence of the gas sensing properties of ZnO nanowires on their microstructure

Two different types of ZnO nanowires were synthesized by the thermal evaporation of different material powders: ZnS powders for ZnO nanowires A; and a mixture of ZnO and graphite powders for ZnO nanowires B. ZnO nanowires A were found to have a bamboo structure consisting of many hexagonal plates each of which is a single crystal, whereas ZnO nanowires B were single crystals with no grain boundary at all. ZnO nanowires B had a far higher degree of preferred orientation than ZnO nanowires A. The sensing properties of ZnO nanowires A were superior to those of ZnO nanowires B in terms of the sensing response and sensing speed. ZnO nanowires A showed an approximately 440 % response at 5 ppm NO2 at 300 °C, whereas ZnO nanowires B showed an approximately 150 % response under the same condition. ZnO nanowires A showed considerably shorter response and recovery times than ZnO nanowires B under the same condition. The superior sensing properties of ZnO nanowires A compared to ZnO nanowires B can be explained mainly by carrier modulation of the depletion layer formed across the grain boundaries of nanowires A.

Physical properties of SnS thin films fabricated by hot wall deposition

The dependence of the microstructure and optical properties of SnS thin films fabricated by hot wall deposition onto glass substrates on the deposition conditions is studied. Phase and elemental composition, surface morphology, and transmission spectra of the obtained films are investigated within the wavelength range 400–2500 nm. The single-phase films feature near-stoichiometric elemental composition and a high degree of preferential orientation in the (040) plane. The optical band gap for direct transitions is 1.07–1.27 eV, depending on film thickness.

Chemically deposited thin films of PbSe as an absorber component in solar cell structures

PbSe thin films were prepared by chemical deposition using dimethylselenourea as a source of selenide ions. Depending on the duration (30 min to 4 h) and temperature (30–60 °C) of the deposition, and the substrate, the films show a high degree of preferred orientation for the (111) planes. The texture coefficients could be up to 5 for these planes. The crystallite diameters are in the 30–35 nm range, and optical bad gap, 0.4–0.7 eV. The electrical conductivity is p-type, 0.01–10 (Ω cm) − 1 . These films were deposited over CdS/Sb 2S 3 or CdS/Sb 2Se 3 solar cell structures as an additional absorber. In a CdS/Sb 2Se 3/PbSe cell, this addition increases the short circuit current density ( J sc ) from 0.2 mA/cm 2 to 8.9 mA/cm 2 and conversion efficiency ( η) from 0.04% to 0.99%. In a CdS/Sb 2S 3/PbSe cell, J sc is 5.91 mA/cm 2; η, 0.98%; and open circuit voltage, 560 mV.

Electrochemical performances for preferred oriented PLD thin-film electrodes of LiNi 0.8Co 0.2O 2, LiFePO 4 and LiMn 2O 4

The charge–discharge performances for lithium ion batteries using the PLD thin-film cathodes of LiNi 0.8Co 0.2O 2, LiFePO 4 and LiMn 2O 4 were investigated. LiMn 2O 4 and LiFePO 4, which have a 3-D frame work crystal structure, showed smooth charging and discharging. On the contrary, LiNi 0.8Co 0.2O 2, which consists of a 2-D layered crystal structure, exhibited a poor discharge capacity. The differences in electro-chemical behaviors might be related to characteristics of PLD thin-film such as high crystallinity or high degree of preferred orientation. Furthermore, the surface roughness and film thickness of LiMn 2O 4 thin-film were varied by using SPT and PLD method, and their structures were clarified by XRD and SEM. The SPT method gave the film with rough and large surface area, while the PLD method provided a flat and high crystalline film. Their rate performances of charge and discharge were independent of the deposition method but depended on the film thickness. Optimum performance was obtained with the PLD film deposited for 30 min, which showed almost the same shape of the discharge curve between 36 C and 720 C.

Sol-gel and PLD Preparation of Lanthanum Gallate-based Mixed Ionic-electronic Conducting Oxides

AbstractIonic and mixed conducting oxides (La0.9Sr0.1)[(Ga1-xFex)0.8Mg0.2]O3-y (I) and (Sr1.8La0.2)(GaFe)O5.1 (II) with the perovskite and brownmillerite structures, respectively, have been prepared in forms of dense bulk ceramics and ceramic coatings by the sol-gel method. Thin films II have been grown by the pulsed laser deposition method on single crystal MgO (100) and Si (100), fused silica, and stainless steel substrates. The films grown under optimal process conditions were single-phase and homogeneous, with a high degree of preferential orientation. The structure and microstructure of the ceramic coatings have been studied by X-ray diffraction and scanning electron microscopy.

Laser deposition of brownmillerite-structure Sr1.8La0.2GaFeO y thin films

Thin films of brownmillerite-structure Sr1.8La0.2GaFeO y have been grown by pulsed laser deposition on (100) MgO, (100) Si, fused silica, and stainless steel substrates, and their microstructure has been studied. The films grown under optimal process conditions are single-phase and homogeneous, with a high degree of preferential orientation.