Crystalline Grain Size Research Articles

CREATION OF COMPOSITE SCINTILLATORS WITH A SHORT DECAY TIME

To date, LuAG:Ce crystals are one of the most common scintillators, since they have been known for a long time and there are technologies for mass production of large-volume crystals. However, the scintillation properties of such crystals can be improved by creating mixed crystals with the replacement of some ions by others. In this work, composite scintillators based on the grown LuYAG:Ce inorganic crystals were produced. For the obtained samples, studies of optical transmission, luminescence, light output, and decay time were carried out. The optimal conditions and sizes of crystalline grains for the creation of composite scintillators have been determined.

Co-deposition of nanocrystalline Co–Mo catalysts with a new fluffy microstructure for hydrogen evolution reaction based on N, N-dimethylformamide and ethylene glycol system

The co-deposition behavior of Co(II) and Mo(VI) in N,N-dimethylformamide and ethylene glycol system is observed. The result implies that Co–Mo co-deposition is typical induced deposition, while containing ordinary deposition process. Mo(VI) species in the system can suppress the reduction of Co(II) and its effect can be improved as the increase of Mo(VI) concentration, however, Co(II) species can promote the reduction of Mo(VI) and the effect can also be improved as the increase of Co(II) concentration. SEM micrographs indicate that all these films exhibit a fibrous surface morphology with a new fluffy microstructure. XRD pattern reveals that the Co–Mo film is a Mo solid solution in Co and its average size of crystalline grain is 9.5 nm. In addition, the electrocatalytic activity for hydrogen evolution reaction (HER) on these Co–Mo films is investigated. These results indicate that its electrocatalytic activity can be improved as Mo content increases from 1.02 to 2.84 wt% and the prepared Co–Mo film with 2.84 wt% Mo presents a high electrocatalytic activity and stability for HER with an overpotential of 81 mV at 10 mA cm−2.

Effect of copolymerization on the thermal characteristics and behavior of crystallization of biobased semi‐aromatic PA10T/10I

AbstractThis work synthesized the pure poly (decamethylene terephthalamide) acid (PA10T) and a series of PA10T/10I through an efficient one‐pot melt polymerization method. The structures, thermal behavior, crystallization performance, and mechanical properties of PA10T and PA10T/10I were investigated by FT‐IR, DSC, TGA, POM, XRD, and mechanics performance testing, respectively. The thermal analysis demonstrates that the melting temperature of PA10T/10I gradually decreased with the increase of isophthalic acid (IPA) copolymerization proportions. Specifically, it was observed that, the Tm1 of pure PA10T was 299.5°C, while the Tm1 of PA10T/10I‐4 with a linear downward trend was 284.7°C. And the introduction of IPA copolymerization has an obvious beneficial effect on the thermal stability of PA10T/10I (Td,5 varied from 429.5 to 434.5°C) with a wider temperature range of processing, which could potentially be applied in high‐temperature scenes. POM and XRD were used to characterize the crystallization behavior of all samples further. It was discovered that although adding IPA did not alter the crystal structure of PA10T, it dramatically reduced the size of crystalline grains and increased the number of crystal nuclei. In addition, the copolyamides possess excellent mechanical properties, and the tensile strength of PA10T/10I varied between 42.91 and 46.89 MPa, the bending strength varied between 76.69 and 85.83 MPa, and the izod impact strength varied between 25.41 and 29.82 kJ m−2. Moreover, the influence of the IPA comonomer of copolyamides PA10T/10I on melting points, thermal stability, crystallization behavior, and mechanical characteristics was investigated. This work provides a reference for preparing biobased semi‐aromatic copolyamides PA10T/10I with outstanding processing performance, excellent thermal characteristics, and adjustable mechanical properties.

Effects of 1,9-dibromnonane on the structural, photophysical properties and stability of cesium lead bromide perovskite nanocrystals

The CsPbBr3@Cs4PbBr6 nanocrystals (NCs) could be synthesized by multiple Cs-oleate injections as adding the 1,9-dibromnonane in the reaction solution. The 1,9-dibromnonane could provide Br− ions and the rich Br− ions effectively restrain the generation of CsBr. The Cs4PbBr6 wrapped around the CsPbBr3 NCs and the size of crystalline grain was increased with increasing the Cs-oleate as excess oleylamine. The quantum yield for 14S4DN reached to 99.3 % due to the decrease of defects and the surface passivation of Cs4PbBr6. There are more oleylammonium bromide on the surface of CsPbBr3 NCs as synthesized with 1,9-dibromnonane. The ligand shell and the surface passivation of Cs4PbBr6 restrained the decomposition of surface, consequently improved the stability of moisture and light for CsPbBr3 NCs. When the CsPbBr3@Cs4PbBr6 NCs were immersed in water under UV light (365 nm) for 2 h, the PL intensity could retain 90.4 %, while the 11S1 (traditional CsPbBr3 NCs) was only 10.9 %. It indicated the stability of moisture and light for CsPbBr3 NCs were greatly improved, because Cs4PbBr6 NCs effectively passivated the surface of CsPbBr3 NCs and restrained the generation of traps states.

Morphological and Structural Variations in Anodic Films grown on Polished and Electropolished Titanium Substrates

The objective of this work was to investigate the effects of anodization parameters on the anatase phase formation of titanium oxide films, which have been grown on both electropolished and non-electropolished titanium surfaces by direct current anodization in 0.25 and 2.5 mol L-1 H3PO4 solutions, respectively, at three anodization times (3, 6 and 12 hours). SEM, Raman spectroscopy and X-ray diffraction techniques revealed the characteristics of anodic films. Films were characterized according to presence of crystalline nuclei of anatase phase on an amorphous matrix. It was found that differences in size, shape and distribution of crystalline grains on anodized surfaces are affected by the type of polishing given to substrates. The particles on electropolished surfaces were grown in well-defined layers following cone-shaped grains. On the other hand, the crystallization phenomenon on non-electropolished substrates has led to the appearance of smaller particle sizes and a larger number of particles distributed along the surface as well.

The Impact of High Pressure, Doping and the Size of Crystalline Boron Grains on Creation of High-Field Pinning Centers in In Situ MgB2 Wires

In this work, we investigated the influence of isostatic pressure (of 0.1 MPa and 1.1 GPa) during heat treatment, doping, size and shape of crystalline boron grains, and annealing time at low annealing temperature (570 °C) on the formation of high-field pinning centers in MgB2 wires. The results indicate that high isostatic pressure (1.1 GPa) at low annealing temperature (570 ° C) and annealing time of 120 min significantly increases the density of high-field pinning centers in MgB2 wires with small and large boron grains. Transport measurements show that an increase of annealing time from 120 to 210 min at 1.1 GPa slightly decreases the critical current density (Jc) and irreversibility field (Birr) in MgB2 wires with large boron grains, suggesting that longer annealing time weakly affects the density of high-field pinning centers. On the other hand, for MgB2 wires with small boron grains, the annealing time of 210 min significantly reduces J_{mathrm {c}} and B_{text {irr}}. This indicates that the longer annealing time at 1.1 GPa significantly reduces the density of high-field pinning centers. Our studies indicate that dislocations created by the hot isostatic pressure process significantly increase B_{text {irr}} in the temperature range from 5 to 12 K. On the other hand, strains due to the shrinkage of MgB2 material increase B_{text {irr}} in the temperature range from 12 to 34 K. The results show that small grains of crystalline boron and high isostatic pressure lead to a high density of dislocations and strains during transformation to the MgB2 phase.

Raman scattering in boron doped nanocrystalline diamond films: Manifestation of Fano interference and phonon confinement effect

Heavily boron doped nanocrystalline diamond films grown on glass substrates by the method of plasma-chemical deposition, were investigated using Raman spectroscopy. Analysis of the spectra showed both the phonon confinement effect in nanocrystalline grains and Fano interference effect due to the contribution of electron Raman scattering in heavily doped p-type diamond films. The increase of boron concentration led to decrease of the size of crystalline diamond grains. The films are semitransparent and have good conductivity, so that it can be used as transparent electrodes in giant-scale electronics and optoelectronics.

Effects of aggregate microstructure on slag resistance of lightweight Al2O3-MgO castable

Corundum-spinel castables using lightweight aggregate have drawn much attention due to their energy-saving potential, in particular when they are applied in high-temperature areas, such as the work lining of refining ladle. One of the main issues which hinder their application is their relatively poor slag corrosion performance. In this study, one type of dense tabular corundum and three types of lightweight corundum were chosen as aggregates to prepare four different model corundum-spinel castables. Their slag resistance was evaluated by an induction furnace corrosion test method. As well as SEM, EDS, and XRD characterizations, thermodynamic and kinetic analyses were carried out to assist understanding the corrosion mechanism. Results indicated that size and shape of crystalline grain in aggregate were important for the slag corrosion (dissolution) resistance of lightweight corundum-spinel castables under dynamic condition (enforced convection), whereas the effects of pore characteristics were not significant. Use of aggregates having large average crystal size and flake-shaped crystals led to a thicker diffusion boundary layer and lowered dissolution rate, i.e., good corrosion resistance, whereas use of aggregates with small and spherical crystals and larger pores led to poor slag resistance.

Influence of synthesis temperatures on the crystalline grain growth and morphology of lanthanum magnesium hexaaluminate

Lanthanum magnesium hexaaluminate (LaMgAl11O19, LMA) was prepared at different temperatures by solid-state reaction. Phase compositions and crystal morphologies of specimens synthesized at different temperatures were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM). It was observed that the crystalline grain size of LMA was not only dependent on the preparation temperature but also on its powder morphology. In the temperature range of 1300–1550 °C, LMA showed platelet grain and the average crystalline grain size increases with the increase in temperature. At 1600 °C, if the powder was sintered for two times, the equiaxed grain could be found with the decrease in grain space, resulting in the reduction of the crystalline grain size. Styles of specimens (powder or disk) might have no obvious influence on morphologies and sizes of LMA crystalline grains which were synthesized with the well-dispersed raw material mixtures. The synthesis temperature played a key role in influencing the free space for the formation and growth of crystalline grains.

Structure, piezoelectric performance and liquid phase aid sintering of SiO2 doped (K0.5Na0.5) NbO3 lead-free ceramics

The structure, piezoelectric and sintering proprieties of Lead-free piezoelectric (K0.5Na0.5) NbO3 (abbreviated as KNN) ceramic with additive SiO2 (KNN–xSiO2, x = 0, 0.25, 0.50, 0. 75, 1.00, 1.50, 2.00 and 3.00 mol%) were investigated. Though it has a high melting point, the SiO2 was found to be effective on the sintering and piezoelectric performance of KNN lead-free ceramics. The structure characterization indicating that low concentration doping (<2.00 mol%) may not change KNN perovskite structure and liquid phase have appeared between crystalline grains. Furthermore, the sizes of crystalline grains gradually increased and reached to maximum when x = 0.75 mol% with indistinct grain boundaries on account of liquid phase. And the density properties of KNN ceramic were dramatically enhanced because of occurrence of liquid phase. The dielectric properties have achieved improvement obviously due to large resistivity and decreased structure loss results from the appearance of liquid phase as well. And ferroelectric properties have still achieved to enhancement including increased remnant polarization P r and decreased coercive field E c when appropriate SiO2 was added into KNLTN ceramic. We obtained the maximum value of piezoelectric coefficient d 33 (115 pC/N) and converse piezoelectric coefficient d * 33 when doping concentration approached to 0.75 mol%.

TEM studies on thermally nanocrystallized vanadium-containing glassy analogs of LiFePO4 olivine

Three series of glasses of the Li2O-FeO-V2O5-P2O5 system were thermally nanocrystallized and their microstructure was studied, at a nanometer resolution by transmission electron microscopy (TEM). Those observations were complemented by DTA and XRD studies on the same materials. It was shown that appropriate heating of the as-received glasses leads to formation of crystalline nanosize grains embedded in the glassy matrix. Average size of those grains reached even a few nm, was much smaller than that reported for LiFePO4-based nanostructured materials obtained by other methods. The crystal structure of most nanograins was identified as that of the LiFePO4 olivine, but some grains of the Nasicon-like Li3V2(PO4)3 phase were also present. The presence of both phases was confirmed independently by XRD patterns. Due to small size of crystalline grains (down to ca 5nm) the interfacial regions around them occupy an important fraction of the total volume of the material and their properties can strongly influence the effective properties of the whole material. We have postulated that the defective nature of interfacial regions leads to an increased concentration of Fe2+/Fe3+, V4+/V5+ or V3+/V4+ aliovalent pairs, crucial for a small polaron hopping mechanism of the electronic transport, and to an enhanced electrical conductivity. The presence of highly conducting interfacial regions in the system where either the glass matrix and both crystalline phases (LiFePO4 and Li3V2(PO4)3) are very poor conductors is the main cause of the observed strong enhancement of the electrical conductivity of the heat-treated glasses of the Li2O-FeO-V2O5-P2O5 system.

Effects of milling on the microstructure and hardness of Al2NbTi3V2Zr high-entropy alloy

Lightweight Al2NbTi3V2Zr alloy was fabricated through mechanical milling and vacuum hot pressing. The effects of milling on the microstructure, phase evolution, and hardness of the fabricated alloy were investigated. High-energy (HE) milling decreased the size of crystalline grains and activated the powders for subsequent sintering. HE-annealed powders at above 900°C and all sintered bulks consisted of body-centered cubic (BCC) and intermetallics α and β. Low-energy (LE) milling only provided homogeneity to the powders. LE bulks exhibited a microstructure similar to that of HE bulks at 1450°C–1550°C. The hardness of the HE bulk was higher than that of the LE bulk and exhibited a peak value of 781HV at 1250°C. All Al2NbTi3V2Zr bulks possessed low density ranging from 5.05g/cm3 to 5.25g/cm3. Two empirical equations for hardness of the bulks were proposed for the BCC matrix bulks and simple cubic matrix bulks respectively and the estimated results are consistent with the experimental measurements.

Micro‐Raman Spectroscopy Study of Glass‐Ceramics with Gradient of Volume Fraction of Crystalline Phase

A simple technique to characterize the structure of nonuniform glass‐ceramics is proposed. The technique is based in micro‐Raman spectroscopy. This technique allows determining the gradient of average size of crystalline grains in the subsurface layers of glass‐ceramics modified by ion exchange.

Deposition of high-electron-mobility transparent conducting zinc oxide thin films by DC magnetron sputtering in gas mixture of argon and hydrogen

Transparent conducting zinc oxide thin films having high electron-mobility are deposited on glass substrates by DC magnetron sputtering in gas mixture of argon and hydrogen at room temperature. Introducing a little amount of hydrogen gas into sputtering Ar gas can remarkedly improve the electron mobility in ZnO thin films. With gas flow rate ratios of hydrogen to argon range from 7.2 % to 19.2 %, ZnO films with hydrogen (ZnO:H) have stable and low resistivity of 6.6×10-4 Ω.cm. At H2/Ar flow rate ratio 7.2 %, electron Hall mobility in ZnO:H film reaches a maximum value of 61 cm2.V-1.s-1. This value is much higher than the one of 23 cm2.V-1.s-1 in pure ZnO films under the same deposition condition. Morever, electron density of 1.51020 cm-3 in ZnO:H films is also higher than the one of 6×1019 cm-3 in pure ZnO films. XRD and FESEM show that the average crystallinegrain size in ZnO:H films are larger than the one in pure ZnO films. The 600-nm-thick ZnO:H films (substrate included) have average transmission of 83 % in the wide wavelength range of 380-1100 nm and low sheet resistance of 11 /square.

Comprehensive Evaluation of the Properties of Nanocrystalline Diamond Coatings Grown Using CVD with E/H Field Glow Discharge Stabilization

The nanocrystalline diamond films (coatings) were prepared using the plasma enhanced chemical vapor deposition (PECVD) technique. In this method, direct current (DC) glow discharge in the crossed E/H fields was used to activate the gas phase. The diamond coatings were deposited from the working gas mixture CH4/H2 with addition of nitrogen in various concentrations. It was ascertained that addition of N2 to the working gas mixture leads to reduction in the sizes of diamond grains as well as to the substantial decrease in the resistivity of the studied films. The electrophysical data are in good agreement with the changes induced by varying the N2 content in the Raman scattering spectra. The increase in the N2 concentration causes significant lowering of the crystalline diamond related peak and increase in the intensity of the peaks related to the sp2‐bonded carbon. These changes in the spectra indicate significant disordering of the structure of prepared films and its uniformity in the nanodiamond film volume. With the great possibility, it is associated with a decrease in the sizes of diamond crystalline grains and tendency of NCD film to amorphization.

Morphology of polycrystalline cassiterite films

Polycrystalline cassiterite films have been grown by the hydropyrolytic method from a 10(H2O) + 5(SnCl2 · 2H2O) solution (in weight fractions) on corundum substrates. The crystallization regularities are considered and a comparative analysis of the properties of natural and artificial cassiterite crystals is performed. The surface morphology is investigated and the size of crystalline grains is determined by scanning electron microscopy. X-ray microprobe analysis showed that all films contain tin and oxygen atoms in a ratio corresponding (within the experimental error) to the chemical formula of tin dioxide. It is established that the surface morphology of cassiterite films is characterized by both single crystallites and aggregates of two or more crystals typical of twins. It is suggest that doping can efficiently be used to control the concentration of twins and the stability of their formation.

Efficient organic photovoltaic cells with vertically ordered bulk heterojunctions

Nanoscale morphology has been proved to be the key parameter deciding the exciton dissociation and charge transportation in bulk heterojunction (BHJ) solar cells. In this paper, we report a kind of small molecular organic photovoltaic cell (OPV) with a vertically ordered BHJ prepared by the weak epitaxial growth method. By this method, zinc phthalocyanine (ZnPc) can easily be formed into a highly ordered and continuous thin film and C60 is inclined to become dispersed crystalline grains in ZnPc film. Furthermore, we can control both the size and distribution density of C60 crystalline grains in ZnPc thin film without destroying the order of the ZnPc thin film. The OPVs with the vertically ordered BHJ show a high fill factor and a power conversion efficiency over 3% has been achieved.

Influence of the microcrystalline structure on the magnetic properties of ferromagnetic films and structures on their base

This paper presents the results of investigating the crystal structure of thin films of the Co40Fe60 composition obtained by magnetron sputtering on their magnetic properties and properties of ferromagnetic nanostructures formed from these films using the optical and electron lithography. It has been found experimentally that magnetic properties of the structures depend on the crystalline-grain sizes, which can be controlled by means of deposition of additional buffer layers of various materials ∼1 nm thick on the substrate under the ferromagnetic film. It has been shown that the crystallite size can be the main factor that determines the minimal lateral sizes of the structures with specified magnetic properties, which are formed from thin ferromagnetic films.

Laser-Induced Epitaxial Growth Technology for Monolithic Three Dimensional Integrated Circuits

Laser-induced epitaxial growth process has been developed to obtain single crystalline silicon on insulator using a seed which is formed by selective epitaxial growth process. It was found that the lateral epitaxial growth of molten silicon occurs when the energy density of the laser beam is high enough to completely melt the deposited amorphous silicon on seeds and that on oxide films. The location and size of such single crystalline grain were precisely controlled due to the pre-patterned epitaxial seeds. Furthermore the problem caused by the edge area of the laser beam was thoroughly analyzed, and solutions to the problem were reasonably suggested. Consequently this proposed laser-induced epitaxial growth process enables the realization of location-controlled perfect single crystalline silicon layer on oxide films for monolithic three-dimensional integration.

Mechanism of boron suppressing environmental embrittlement in H2 for the ordered Ni3Fe intermetallics

Influence of boron content on tensile properties in vacuum and H2 atmosphere as well as hydrogen diffusion effect for the ordered Ni3Fe intermetallics were investigated. The results showed that the ultimate tensile strength and elongation of the ordered Ni3Fe alloy tested in vacuum and H2 increased and the factor of hydrogen embrittlement of the alloy in H2 decreased with increasing the boron content in the alloy. The tensile fractographs tested in vacuum and H2 illustrated that the boron atom doping in the ordered Ni3Fe alloy increased the grain boundary strength. The diffusion coefficient of hydrogen in the ordered Ni3Fe decreased with the increase of boron content. The diffusion of hydrogen played the main role in the process of hydrogen embrittlement when the ordered Ni3Fe alloy tested in H2. The mechanism of boron suppressing the environmental embrittlement induced by H2 is that the boron segregated on the boundary of the ordered Ni3Fe alloy decreases the size of crystalline grain and increases the mechanical property of the alloy; meanwhile, boron increases also the grain boundary strength and decreases the diffusion coefficient of hydrogen. Therefore, the boron atom can reduces effectively the sensitivity of hydrogen embrittlement of the ordered Ni3Fe alloy in H2.