Microcrystalline Material Research Articles

Cs2Cd(C2H)2(C2): A Crystalline Acetylide with Bridging C2 Units.

Cs2Cd(C2H)2(C2) was synthesized by heating known Cs2Cd(C2H)4 either in a dry argon atmosphere at 200 °C or under ammonothermal conditions (130 °C, ∼ 100 bar). The crystal structure of the resulting dark orange-brown microcrystalline material was solved and refined from synchrotron powder diffraction data (Cmcm, Z = 4). Cs2Cd(C2H)2(C2) is composed of Cd2+ cations tetrahedrally coordinated end-on by four acetylide groups. Two of them are terminating C2H- groups, whereas the other two positions are occupied by bridging C22- anions. Thus, a polymeric ∞1[Cd(C2H)2(C2)2/22-] chain-like anion results and these chains are separated by Cs+ cations. So obviously Cs2Cd(C2H)2(C2) is formed from Cs2Cd(C2H)4 by a condensation reaction of two of its four C2H- groups under the release of one acetylene (C2H2) molecule. This reaction mechanism is supported by DSC/TGA measurements, and the crystal structure of Cs2Cd(C2H)2(C2) is further supported by IR spectroscopic investigations.

Discolouration of polyamide microcrystalline denture base plates after exposure to filter cigarette smoke

Introduction: Denture users with smoking habit often complain about colour changes in their dentures, especially on the base part. Polyamide microcrystalline is a thermoplastic denture base material and does not undergo many colour changes. The purpose of this study was to analyse the effect of filter cigarettes smoke exposure on the colour of polyamide microcrystalline materials. Methods: This study used posttest only control group design — Plate-Shaped sample with a size of 2 x 2 x 0.5 cm3. Nine samples as controls were immersed without exposure to the cigarette smoke, and 9 samples were immersed in artificial saliva with exposure to the filter cigarette smoke by six cycles, where one cycle was in the form of smoke exposure from one cigarette at 30-minute intervals. Cigarette exposure lasts for 21 days using a smoking simulation tool. Every seven days of exposure, colours were evaluated using a DSLR camera. The photos were then analysed with Adobe™ Photoshop in the CIELab colour space. The results were analysed afterwards by a one-way ANOVA variant test, and advance difference tests were analysed using a Post-Hoc test. Results: There was a significant colour change after exposure (p < 0.05), but the control group did not experience discolouration. The highest rate of colour change occurred in the second week, while in the third week the colour changes still occurred but tend to be stable. Conclusion: Exposure to the filter cigarette smoke changes the colour of polyamide microcrystalline denture base.Keywords: Polyamide microcrystalline, filter cigarette smoke, discolouration, denture base

Dual-band simultaneous lasing in MOFs single crystals with Fabry-Perot microcavities

Multi-band microlasers based on single microcrystalline materials with Fabry-Perot (F-P) cavities are critically and technologically essential. Here, we demonstrate simultaneous dual-band lasing output (615 and 685 nm) in metal-organic frameworks (MOFs) and organic dyes hybrid single crystals, which support F-P resonances. Through a two-step assembly strategy, two different types of cationic pyridinium hemicyanine dye molecules can be encapsulated into the channel pores of anionic bio-MOF-1-2Me successfully. In addition, the employment of the host-guest system significantly increases the dye loading, enhances luminescent efficiency, and diminishes the aggregation-caused quenching (ACQ) effect in the resultant MOFs/dye composites. This finding not only combines the characteristic of MOFs materials with excellent luminescent properties of organic dyes, but also points out a simple and promising strategy to design multi-band microlasers based on F-P mechanism, opening a low-cost avenue for the rational design of miniaturized lasers in the future.

On the Structure and Thermoelectric Properties of CoSi Obtained from a Supersaturated Solution–Melt in Sn

The structure, composition, and thermoelectric properties of cobalt monosilicide obtained by crystallization from a supersaturated solution–melt in tin are studied. A technique for the synthesis and directional solidification of microcrystalline and bulk textured materials in a single technological cycle is developed.

Thermoluminescence studies of CaSO4:Dy nanophosphor for application in high dose measurements

Nanorods of CaSO4:Dy (having diameter ∼20 nm and length ∼200 nm) were prepared by chemical coprecipitation method and their thermoluminescence (TL) characteristics were studied after annealing at different temperatures in the range 400–1000 °C. Microcrystalline material was also prepared through acid recrystallization method. TL glow curves of the nanocrystalline material annealed at 700 °C showed a major peak at around 283 °C. The effect of annealing temperature on the phase structure/morphology of particles was studied. Phase change was observed when CaSO4:Dy was annealed at different temperatures as confirmed by XRD and TG-DTA. It was observed from the TEM images that the nanomaterial originally in the nanorods form broke into nanoparticles due to strain developed by phase change on annealing at higher temperatures. The combined effect resulted in changes in TL glow curve structure. For better clarity the TL glow curves were further deconvoluted by Computerized Glow Curve Deconvolution (CGCD) method and kinetic trapping parameters were determined. It was found that the values of kinetic parameters also changed for the nanocrystalline material annealed at different temperatures. These were also compared with the corresponding values of the microcrystalline material. It was also observed that the TL intensity saturates at about 100 Gy in case of microcrystalline phosphor, while that in case of nanocrystalline phosphor did not do saturate even up to 5 kGy.

Photochemical synthesis of nano- and micro-crystalline particles in aqueous solutions

UV irradiation of aqueous solutions containing various metal ions (Ag, Rh, Cu, Pb, Ba, …) and sensitizers was performed in order to synthesize a large variety of solid nano- or microcrystalline materials in the irradiated solutions and illustrate the chemical and photochemical reactions leading to their formation. Acetone was shown to be a very effective sensitizer and photoreducing agent when coupled with propan-2-ol, whereas formate HCOO– was introduced either mainly as a reducing agent in deaerated solution or as a source of nascent CO2 in the presence of air. It was shown that UV irradiation allows for the preparation of a wide variety of inorganic materials. Moreover, reactions mechanisms discussed may occur during Laser Ablation in Liquid processes.

Структура и термоэлектрические свойства CoSi, полученного из пересыщенного раствора-расплава в Sn

AbstractThe structure, composition, and thermoelectric properties of cobalt monosilicide obtained by crystallization from a supersaturated solution–melt in tin are studied. A technique for the synthesis and directional solidification of microcrystalline and bulk textured materials in a single technological cycle is developed.

Calcium ion incorporated hydrous iron(III) oxide: synthesis, characterization, and property exploitation towards water remediation from arsenite and fluoride.

Calcium ion-incorporated hydrous iron(III) oxide (CIHIO) samples have been prepared aiming investigation of efficiency enhancement on arsenic and fluoride adsorption of hydrous iron(III) oxide (HIO). Characterization of the optimized product with various analytical tools confirms that CIHIO is microcrystalline and mesoporous (pore width, 26.97 Å; pore diameter, 27.742 Å with pore volume 0.18 cm3 g-1) material. Increase of the BET surface area (> 60%) of CIHIO (269.61 m2 g-1) relative to HIO (165.6 m2 g-1) is noticeable. CIHIO particles are estimated to be ~ 50 nm from AFM and TEM analyses. Although the pH optimized for arsenite and fluoride adsorptions are different, the efficiencies of CIHIO towards their adsorption are very good at pH 6.5 (pHzpc). The adsorption kinetics and equilibrium data of either tested species agree well, respectively, with pseudo-second order model and Langmuir monolayer adsorption phenomenon. Langmuir capacities (mg g-1at 303 K) estimated are 29.07 and 25.57, respectively, for arsenite and fluoride. The spontaneity of adsorption reactions (ΔG0 = - 18.02 to - 20.12 kJ mol-1 for arsenite; - 0.2523 to - 3.352 kJ mol-1 for fluoride) are the consequence of entropy parameter. The phosphate ion (1 mM) compared to others influenced adversely the arsenite and/or fluoride adsorption reactions. CIHIO (2.0 g L-1) is capable to abstract arsenite or fluoride above 90% from their solution (0 to 5.0 mg L-1). Mechanism assessment revealed that the adsorption of arsenite occurs via chelation, while of fluoride occurs with ion-exchange.

Confinement of Perovskite-QDs within a Single MOF Crystal for Significantly Enhanced Multiphoton Excited Luminescence.

The development of the photostable higher-order multiphoton-excited (MPE) upconversion single microcrystalline material is fundamentally and technologically important, but very challenging. Here, up to five-photon excited luminescence in a host-guest metal-organic framework (MOF) and perovskite quantum dot (QD) hybrid single crystal ZJU-28⊃MAPbBr3 is shown via an in situ growth approach. Such a MOF strategy not only results in a high QD loading concentration, but also significantly diminishes the aggregation-caused quenching (ACQ) effect, provides effective surface passivation, and greatly reduces the contact of the QDs with the external bad atmosphere due to the confinement effect and protection of the framework. These advantages make the resulting ZJU-28⊃MAPbBr3 single crystals possess high PLQY of ≈51.1%, a high multiphoton action cross-sections that can rival the current highest record (measured in toluene solution), and excellent photostability. These findings liberate the excellent luminescence and nonlinear optical properties of perovskite QDs from the solution system to the solid single-crystal system, which provide a new avenue for the exploitation of high-performance multiphoton excited hybrid single microcrystal for future optoelectronic and micro-nano photonic integration applications.

Computer simulation of superplastic forming of a three-sheet structure containing an ultrafine-grained core

Superplastic forming of a three-sheet structure is considered. The focus is on overcoming the main disadvantages of the process of manufacturing of such structures by means of the SPF/DB technique including high temperatures of treatment and the formation of folds on the outer surface of the article manufactured. The application of ultrafine-grained sheets of titanium alloy Ti-6Al-4V has been analyzed in order to avoid these disadvantages. Various combinations of the use of ultrafine-grained and microcrystalline sheets as skin and core sheets are considered by means of the finite element analysis. The standard power law of superplasticity is used for analysis with material constants determined from technological experiments. The conclusion is made that the most attractive way appears to be the usage of ultafine-grained material for the core sheet and microcrystalline material for the skin sheets.

Unexpected Sequential NH3/H2O Solid/Gas Phase Ligand Exchange and Quasi-Intramolecular Self-Protonation Yield [NH4Cu(OH)MoO4], a Photocatalyst Misidentified before as (NH4)2Cu(MoO4)2.

[NH4Cu(OH)MoO4] as active photocatalyst in the decomposition of Congo Red when irradiated by UV or visible light has been prepared in an unusual ammonia/water ligand exchange reaction of [tetraamminecopper(II)] molybdate, [Cu(NH3)4]MoO4. [Cu(NH3)4]MoO4 was subjected to moisture of open air at room temperature. Light blue orthorhombic [Cu(NH3)(H2O)3]MoO4 was formed in 2 days as a result of an unexpected solid/gas phase ammonia-water ligand exchange reaction. This complex does not lose its last ammonia ligand on further standing in open air; however, a slow quasi-intramolecular (self)-protonation reaction takes place in 2-4 weeks, producing a yellowish-green microcrystalline material, which has been identified as a new compound, [NH4Cu(OH)MoO4], ( a = 10,5306 Å, b = 6.0871 Å, c = 8.0148 Å, β = 64,153°, C2, Z = 4). Mechanisms are proposed for both the sequential ligand exchange and the self-protonation reactions supported by ab initio quantum-chemical calculations and deuteration experiments as well. The [Cu(NH3)(H2O)3]MoO4 intermediate transforms into NH4Cu(OH)(H2O)2MoO4, which loses two waters and yields [NH4Cu(OH)MoO4]. Upon heating, both [Cu(NH3)4]MoO4 and [Cu(NH3)(H2O)3]MoO4 decompose, losing three NH3 and three H2O ligands, respectively, and stable [Cu(NH3)MoO4] is formed from both. The latter can partially be hydrated in boiling water into [NH4Cu(OH)MoO4. This compound can also be prepared in pure form by boiling the saturated aqueous solution of [Cu(NH3)4]MoO4. All properties of [NH4Cu(OH)MoO4] match those of the active photocatalyst described earlier in the literature under the formulas (NH4)2[Cu(MoO4)2] and (NH4)2Cu4(NH3)3Mo5O20.

Grain size effects on irradiated CeO2, ThO2, and UO2

Microcrystalline and nanocrystalline UO2, ThO2, and CeO2 (∼2 μm and∼20 nm particle size, respectively) were irradiated with 946 MeV Au ions at room temperature and characterized by synchrotron X-ray diffraction, Raman spectroscopy, and transmission electron microscopy. All samples show a small increase in unit cell parameter as a function of ion fluence (0.17 ± 0.03% for CeO2 and 0.11 ± 0.03% for ThO2), except microcrystalline UO2, which displays a small contraction of the unit cell (−0.06 ± 0.02%). Raman spectroscopy measurements of microcrystalline UO2 indicate an increase in nonstoichiometry after irradiation. All bulk materials are subject to an increase in heterogeneous microstrain, most notably UO2, implying that the relatively small changes in unit cell parameter are accompanied by substantial local disorder induced by isolated defects. The magnitude of volumetric swelling for all materials is larger in the nanocrystalline form as compared with the microcrystalline form (0.38 ± 0.60% for CeO2, 0.14 ± 0.03% for ThO2, and 0.52 ± 0.13% for UO2). ThO2 shows the smallest difference in swelling between the microcrystalline and nanocrystalline samples (∼0.03%). All nanocrystalline materials exhibit irradiation-induced grain coarsening along with a decrease in heterogeneous microstrain with increasing ion fluence, except nanocrystalline CeO2, which shows no observable change in grain size and a slight increase in heterogeneous microstrain attributed to the accelerated formation of a secondary Ce11O20 phase evidenced in the X-ray diffraction data, present in both nanocrystalline and microcrystalline materials. Surprisingly, nanocrystalline UO2 exhibits a significant degree of swelling indicative of a decrease in oxygen content along with an increase in disorder induced by oxygen loss at grain boundaries during irradiation, based on the analysis of X-ray diffraction and Raman spectroscopy.

Optical constants and electrochromic characteristics of HxMoO3 and LixMoO3 bronzes.

Ellipsometric concentration dependent data of ZxMoO3 (Z=H+, Li+) bronze thin films are interpreted from different prospects to unravel a detailed account of electrochromic characteristics. From the linear parts of the electronic energy loss functions (-1/ϵ), and from the dips in the optical density data, it is very difficult to decide about crystallographic phase shifts in these bronzes, simply because of the difficulty of the structural determination of these microcrystalline materials. MoO3 bronze thin films are found to have high electrochromic efficiency, and therefore require higher charge density, and less substoichiometry, to obtain the same contrast ratio as observed in tungsten bronze thin films. The values of oscillator strengths, dipole strengths, and the degrees of delocalization of polaron wave functions have been calculated at different doping levels, and all are found to reveal the characteristics of localized in-bandgap states of electrons, and do not give any symptom of formation of Bloch states in these bronzes even at higher values of concentration, x.

Photoluminescence properties of green emitting CaY2Al4SiO12:Tb3+ garnet phosphor

The photoemission properties of a microcrystalline-powder Tb3+-doped CaY2Al4SiO12 garnet phosphor were studied. The microcrystalline materials were obtained using the sol–gel method that yields chemically homogeneous and microparticle-sized powders. X-ray powder diffraction (XRPD) and scanning electron microscope (SEM) analyses were used to reveal the crystallinity, crystal structure, and surface morphology of the prepared CaY2Al4SiO12:Tb3+ garnet phosphor. The samples showed a green-emission characteristic at around 544 nm with an excitation at 271 nm. A concentration quenching was observed with the increasing of the Tb3+ concentration. The effect of the Tb3+ doping and the photoluminescence properties were also investigated, leading to the proposal of a feasible interpretation by the authors.

The Role of a Phonon Bottleneck in Relaxation Processes for Ln-Doped NaYF4 Nanocrystals

The localized inner 4f shell transitions of lanthanide ions are largely independent of the local surroundings. The luminescence properties of Ln3+ ions doped into nanocrystals (NCs) are therefore similar to those in bulk crystals. Quantum size effects, responsible for the unique size-dependent luminescence of semiconductor NCs, are generally assumed not to influence the optical properties of Ln3+-doped insulator NCs. However, phonon confinement effects have been reported to hamper relaxation between closely spaced Stark levels in Ln3+-doped NCs. At cryogenic temperatures emission and excitation from higher Stark levels was observed for Ln3+ ions in NCs only and were explained by a cutoff in the acoustic phonon spectrum. Relaxation would be inhibited as no resonant low energy (long wavelength) acoustic phonon modes can exist in nanometer sized crystals, and this prevents relaxation by direct phonon emission between closely spaced Stark levels. This phenomenon is known as a phonon bottleneck. Here, we investigate the role of phonon confinement in Ln-doped NCs. High resolution emission spectra at temperatures down to 2.2 K are reported for various Ln3+ ions (Er3+, Yb3+, Eu3+) doped into monodisperse 10 nm NaYF4 NCs and compared with spectra for bulk (microcrystalline) material. Contrary to previous reports, we find no evidence for phonon bottleneck effects in the emission spectra. Emission from closely spaced higher Stark levels is observed only at high excitation powers and is explained by laser heating. The present results indicate that previously reported effects in NCs may not be caused by phonon confinement.

The cause of ‘weak-link’ grain boundary behaviour in polycrystalline Bi2Sr2CaCu2O8 and Bi2Sr2Ca2Cu3O10 superconductors

The detrimental effects of grain boundaries have long been considered responsible for the low critical current densities in high temperature superconductors. In this paper, we apply the quantitative approach used to identify the cause of the ‘weak-link’ grain boundary behaviour in YBa2Cu3O7 (Wang et al 2017 Supercond. Sci Technol. 30 104001), to the Bi2Sr2CaCu2O8 and Bi2Sr2Ca2Cu3O10 materials that we have fabricated. Magnetic and transport measurements are used to characterise the grain and grain boundary properties of micro- and nanocrystalline materials. Magnetisation measurements on all nanocrystalline materials show non-Bean-like behaviour and are consistent with surface pinning. Bi2Sr2CaCu2O8: our microcrystalline material has very low grain boundary resistivity which is similar to that of the grains such that (assuming a grain boundary thickness (d) of 1 nm) equivalent to an areal resistivity of The transport values are consistent with well-connected grains and very weak grain boundary pinning. However, unlike low temperature superconductors (LTS) in which decreasing grain size increases the pinning along the grain boundary channels, any increase in pinning produced by making the grains in our Bi2Sr2CaCu2O8 materials nanocrystalline was completely offset by a decrease in the depairing current density of the grain boundaries caused by their high resistivity. We suggest a different approach to increasing from that used in LTS materials, namely incorporating additional strong grain and grain boundary pinning sites in microcrystalline materials to produce high values. Bi2Sr2Ca2Cu3O10: both our micro- and nanocrystalline samples have of at least 103. This causes strong suppression of across the grain boundaries, which explains the low transport values we find experimentally. Our calculations show that low in untextured polycrystalline Bi2Sr2Ca2Cu3O10 material is to be expected and the significant effort in the community in texturing samples and removing grain boundaries altogether is well-founded.

Hot pressing of nanocrystalline tantalum using high frequency induction heating and pulse plasma sintering

The paper presents the results of nanocrystalline powder tantalum consolidation using hot pressing. The authors used two different heating techniques during hot pressing: high-frequency induction heating (HFIH) and pulse plasma sintering (PPS). A comparison of the structure, microstructure, mechanical properties and corrosion resistance of the bulk nanocrystalline tantalum obtained in both techniques was performed. The nanocrystalline powder was made to start from the microcrystalline one using the high-energy ball milling process. The nanocrystalline powder was hot-pressed at 1000 °C, whereas, for comparison, the microcrystalline powder was hot pressed up to 1500 °C for proper consolidation. The authors found that during hot pressing, the powder partially reacts with the graphite die covered by boron nitride, which facilitated punches and powder displacement in the die during densification. Tantalum carbide and boride in the nanocrystalline material was found, which can improve the mechanical properties. The hardness of the HFIH and PPS nanocrystalline tantalum was as high as 625 and 615 HV, respectively. The microstructure was more uniform in the PPS nanomaterial. The corrosion resistance in both cases deteriorated, in comparison to the microcrystalline material, while the PPS material corrosion resistance was slightly better than that of the HFIH one.

Color changing in denture base polyamide 12 and polyamide microcrystalline after polishing in laboratory and dental clinic

This study’s purpose was to compare color changes from polyamide 12 and polyamide microcrystalline materials. Each material was divided into two groups, polished with laboratory and clinical polishing equipment, and then immersed in a 28 °C coffee solution for seven days. Surface roughness was measured with a profilometer before the immersion. Color (L*, a*, and b*) was measured using a spectrophotometer before and after immersion. There were no significant color changes in the polyamide 12 and polyamide microcrystalline materials after immersion in the coffee solution.

Influence of excitation frequency and electrode separation on the growth of microcrystalline silicon films and their application in single junction microcrystalline solar cell

In this paper we present the role of plasma excitation frequency and electsrode separation on the growth of microcrystalline silicon thin films at two different hydrogen dilutions of silane and different power densities. We optimized the process conditions to develop device quality microcrystalline material. Optoelectronic and structural properties of the developed material have been correlated with the solar cell properties. Growth rate ~7 A/s has been achieved using plasma excitation frequency of 27.12 MHz at 15 mm electrode separation. We have noticed the positive effects after reducing the electrode separation in higher frequency (27.12 MHz). Optimized microcrystalline film of activation energy 0.55 eV and grain size of 14.61 nm has been developed and is applied to fabricate single junction microcrystalline solar cell. Solar cell with initial cell efficiency of 7.75% with short circuit current density of 24.98 mA/cm2 and open circuit voltage of 0.47 V and fill factor of 0.66 has been achieved.

Micro-mechanical modelling of mechanical and electrical properties in homogeneous piezoelectric ceramic by using boundary integral formulations

Recent experiments on polycrystalline materials show that microcrystalline materials have a strong dependency ona grain size. In this study, mechanical and electrical properties of polycrystalline materials in micro level were studied by using averaging theorems. To completely understand the size-dependency of polycrystalline materials, an integral non-local approach that can predict the stress-strain relations for these materials was presented. In microcrystalline materials, crystalline and grain-boundary were considered as two separate phases. Mechanical properties of the crystalline phase were modelled using crystalline brittle material and is composed of randomly distributed and orientated single crystal anisotropic elastic grains. For microcrystalline materials, the surface-to-volume ratio of the grain boundaries is low enough to ignore its contribution to the elastic deformation. Therefore, the grain boundary phase was not considered in microcrystalline materials and mechanical properties of the crystalline phase were modelled using appropriate integral non-local approach. Finally, the constitutive equations for polycrystalline materials were implemented into a boundary integral equation and the results and some examples are provided for piezoelectric ceramic.