Fabrication of Aluminum Oxynitride (γ‐AlON) Transparent Ceramics with Modified Gelcasting

Transparent aluminum oxynitride (AlON) ceramics have been prepared through aqueous gelcasting forming technique starting from the raw materials of single phase AlON powders. The powder was specially treated for anti‐hydrolysis in ethanol before the shaping technique. The surface‐treated AlON powders could then be dispersed in an aqueous‐organic solution to prepare stable slurries containing 35 vol% solids loading. The obtained stable slurries were subsequently casted, calcined, and pressureless sintered at 1950°C for 8 h in nitrogen atmosphere. High transparent AlON ceramics with an average grain size of 112 μm and the in‐line transmittance of 81% at wavelength 1100 nm have been obtained.     

Elastic Properties of Polycrystalline Aluminum Oxynitride Spinel and Their Dependence on Pressure, Temperature, and Composition

The isotropic elastic moduli of four specimens of nitrogen-stabilized cubic aluminum oxide (ALON) were measured using pulse superposition interferometry. Experiments were carried out as a function of both pressure (ambient to 1 GPa) and temperature (0° to 25°C) for specimens of 30.0 and 35.7 mol% AlN. The second-order moduli results were corrected for porosity using the "self-consistent-scheme" approach. Pertinent ambient results for isotropic pore-free ALON are K = 226.3 GPa and G = 132.0 GPa for the 30.0 mol% AlN material, and K = 229.8 GPa and G = 135.5 GPa for 35.7 mol% ALON ( K and G denote the bulk and shear moduli, respectively). The estimated uncertainties in these values are about 2%. The second-order elastic properties of ALON, as well as their pressure and temperature derivatives, fall midway between spinel (MgAl₂O₄) and corundum (Al₂O₃), indicating the excellent potential of this material for structural engineering purposes.     

Elastic Properties of Taurine Single Crystals Studied by Brillouin Spectroscopy

The inelastic interaction between the incident photons and acoustic phonons in the taurine single crystal was investigated by using Brillouin spectroscopy. Three acoustic phonons propagating along the crystallographic b-axis were investigated over a temperature range of −185 to 175 °C. The temperature dependences of the sound velocity, the acoustic absorption coefficient, and the elastic constants were determined for the first time. The elastic behaviors could be explained based on normal lattice anharmonicity. No evidence for the structural phase transition was observed, consistent with previous structural studies. The birefringence in the ac-plane indirectly estimated from the split longitudinal acoustic modes was consistent with one theoretical calculation by using the extrapolation of the measured dielectric functions in the infrared range.     

Crystal Structure and Elastic Properties of Hypothesized MAX Phase‐Like Compound (Cr2Hf)2Al3C3

The term “MAX phase” refers to a very interesting and important class of layered ternary transition‐metal carbides and nitrides with a novel combination of both metal and ceramic‐like properties that have made these materials highly regarded candidates for numerous technological and engineering applications. Using (Cr₂Hf)₂Al₃C₃ as an example, we demonstrate the possibility of incorporating more types of elements into a MAX phase while maintaining the crystallinity, instead of creating solid solution phases. The crystal structure and elastic properties of MAX phase‐like (Cr₂Hf)₂Al₃C₃ are studied using the Vienna ab initio Simulation Package. Unlike MAX phases with a hexagonal symmetry (P6₃/mmc, #194), (Cr₂Hf)₂Al₃C₃ crystallizes in the monoclinic space group of P2₁/m (#11) with lattice parameters of a = 5.1739 Å, b = 5.1974 Å, c = 12.8019 Å; α = β = 90°, γ = 119.8509°. Its structure is found to be energetically much more favorable with an energy (per formula unit) of ?102.11 eV, significantly lower than those of the allotropic segregation (?100.05 eV) and solid solution (?100.13 eV) phases. Calculations using a stress versus strain approach and the VRH approximation for polycrystals also show that (Cr₂Hf)₂Al₃C₃ has outstanding elastic moduli.     

Phase Relations and Reaction Sintering of Transparent Cubic Aluminum Oxynitride Spinel (ALON)

A new isobaric, condensed phase diagram in the region of stability of cubic aluminum oxynitride spinel (ALON) along the pseudobinary AI₂O₃-AIN composition join is presented, deduced primarily from various analytical measurements and microstructural observations. It is shown that cubic aluminum oxynitride spinel melts incongruently at ≊2050°C and is compositionally centered at ≊35.7 mol% AIN, which is equivalent to the following stoichiometric composition: AI₂₃O₂₇N₅ or 5AIN·9AI₂O₃. Single-phase ALON material sintered to nearly full density exhibits transparency in visible light.     

晶体8-羟基喹啉铝的合成及光致和电致发光性能

采用水热合成法,得到8-羟基喹啉铝金属配合物。对8-羟基喹啉铝的单晶进行了X-射线衍射分析,确定了结构;同时对此配合物的UV—VIS-NIR,荧光光谱进行了测定和分析,并且以8-羟基喹啉铝的单晶作为发光材料制成器件对其电致发光性能进行了对比研究。     

Diffusion Characteristics of Zr4+ in LiNbO3 Single‐Crystal

Diffusion characteristics of Zr⁴⁺ in LiNbO₃ single‐crystal were studied. Zr⁴⁺‐doped LiNbO₃ crystal plates were prepared by in‐diffusion of 100 nm thick ZrO₂ film coated onto Z‐cut congruent substrates in wet O₂ at different temperatures. Zr⁴⁺‐diffused profile was analyzed by secondary ion mass spectrometry. The results show that the Zr⁴⁺ diffusion follows the traditional diffusion theory. From the measured profiles, important diffusion parameters are obtained, such as diffusivity and its temperature dependence, diffusion constant, activation energy, surface concentration, and solubility. The Zr⁴⁺ has a diffusivity similar to that of Ti⁴⁺, implying that the Zr⁴⁺ doping and the Ti⁴⁺ diffusion can be performed simultaneously to simplify the fabrication process of a photorefractive‐damage‐resistant Zr⁴⁺‐doped Ti‐diffused LiNbO₃ waveguide.     

Size‐Dependent Crystal Properties of Nanocuprite

Cuprite nanoparticles from 9 nm to 1 μm with narrow size distribution (±7%) are prepared by two different methods. The lattice parameter increases up to 0.2% as the crystallite size decreases to 9 nm from micron size. X‐ray Absorption Near Edge Spectroscope study of our copper oxide nanoparticles shows mostly Cu (I) with increasing concentration of Cu (II) as decreasing crystal sizes. The size effect in Cu(II)/Cu(I) ratio indicates that at smaller crystal size, the Cu₂O tends to be more oxidized at higher charge state with Cu(I)‐O bond. Thus, the lattice expansion can be explained by the presence of longer Cu (II)‐O bond than Cu (I)‐O bond and/or oxygen interstitials in nanocuprite.     

Preparation and Properties of Oxynitride Glasses Made from Potassium Metaphosphate

Potassium phosphate oxynitride (KPON) glasses were made by heating crystalline KPO₃ at 702^° to 775^°C in dry ammonia. The softening temperature, thermal expansion coefficient, refractive index, and dissolution rate in water were measured as a function of nitrogen content and compared with the properties of oxynitride glasses made from LiPO₃ and NaPO₃.     

Single‐Crystalline Mesoporous Molybdenum Nitride Nanowires with Improved Electrochemical Properties

We report single‐crystalline mesoporous molybdenum nitride nanowires (meso‐Mo₃N₂‐NWs) prepared by topotactic reaction using single‐crystalline molybdenum oxide nanowires. The single‐crystalline nature of meso‐Mo₃N₂‐NWs was clearly observed by field‐emission transmission electron microscopy. The meso‐Mo₃N₂‐NWs exhibited mesoporous structure with ～45 m²/g in specific surface area and ～4.6 nm in average pore size confirmed by a nitrogen sorption measurement. Due to high specific surface area and mesoporous structure, meso‐Mo₃N₂‐NWs showed much higher specific capacitance and excellent charging–discharging performance as compared with Mo₃N₂ prepared using conventional nitridation process.     

Unusual Crystal Growth Kinetics of (RS)‐Ibuprofen from Ethanolic Solutions

The solubility, secondary nucleation threshold, and growth kinetics of (RS)‐ibuprofen have been studied in an aqueous ethanol solvent. The metastable zone for secondary nucleation is very narrow at lower temperatures in this range, but greatly enlarged at higher temperatures. The crystal growth kinetics not only display significant dispersion of growth rates, but also a dead zone that is dependent on the growth rates of the crystals. Faster growing crystals display almost no dead zone, whereas the smallest crystals have a large dead zone. The size of the dead zone is largely responsible for the dispersion of crystal growth rates, perhaps due to differences in the thermodynamic stability of the different crystals. The mechanism of growth rate dispersion relates to that of the dead zone.     

Solubility Limits of La and Y in Aluminum Oxynitride at 1870°C

The solubility limits of important dopants (La and Y) in aluminum oxynitride (AlON) were measured using wavelength-dispersive spectroscopy (WDS) mounted on a scanning electron microscope, from samples quickly cooled from 1870°C. To provide saturated AlON, samples were prepared with dopant concentrations well above the solubility limit, which was confirmed by the appearance of secondary phases using X-ray diffraction, backscattered electron micrographs, and WDS. Measurements were conducted on polished samples without thermal or chemical etching. The results indicate solubility limits of 498±82 and 1775±128 ppm for La and Y in AlON at 1870°C, respectively. The solubility limit of Mg in AlON at 1870°C was found to be >4000 ppm. The relation between solubility limit and cation size is briefly discussed.     

Low‐Temperature Ionic Conductivity of an Acceptor‐Doped Perovskite: I. Impedance of Single‐Crystal SrTiO3

Low‐temperature conductivity mechanisms were identified in acceptor‐doped SrTiO₃ single crystals quenched from high temperatures under reducing conditions. Impedance spectroscopy measurements made on samples of the prototypical perovskite structure doped with iron provided a framework for creating a complete conductivity model for a well‐defined point defect system. The dominant conductivity mechanism in the room‐temperature range was identified as being controlled by oxygen vacancy hopping. The activation energy for oxygen vacancy migration, an often debated value in the perovskite community, is determined to lie within the range of 0.59–0.78 eV for the iron‐doped system with the bottom of this range approaching the intrinsic value for oxygen vacancy hopping in an undoped single crystal. At low temperatures, oxygen vacancies form defect complexes with iron impurities, and the observed range of activation energies is explained and modeled in terms of an oxygen vacancy trapping mechanism.     

Elastic Properties and Structure of Interpenetrating Boron Carbide/Aluminum Multiphase Composites

We study the elastic moduli and structure of boron carbide/aluminum (B₄C/Al) multiphase composites using rigorous bounding and experimental characterization techniques. We demonstrate that rigorous bounds on the effective moduli are useful in that they can accurately predict (i) the effective elastic moduli, given the phase moduli and volume fractions, or (ii) the phase moduli (volume fractions), given the effective moduli and phase volume fractions (moduli). Using the best available rigorous bounds on the effective elastic moduli of multiphase composites involving volume-fraction information, we are able to predict the bulk and shear moduli of the Al₄BC phase, a reaction product that forms during heat treatment. These theoretical predictions are in very good agreement with recent experimental measurements of the moduli of the Al₄BC phase. Moreover, we evaluate more-refined bounds involving three-point structural correlation functions by extracting such information from an image of a sample of the B₄C/Al composite. Although experimental data for the effective moduli are unavailable for this sample, our predictions of the effective moduli based on three-point bounds should be quite accurate.     

Low Temperature Ionic Conductivity of an Acceptor‐Doped Perovskite: II. Impedance of Single‐Crystal BaTiO3

Low temperature conductivity mechanisms were identified in acceptor‐doped BaTiO₃ single crystals equilibrated and quenched from high temperature under different oxygen partial pressures. A range of acceptor ionization states were quenched into samples doped with manganese or iron. Using an appropriate equivalent circuit to interpret impedance spectroscopy data, room temperature conductivity mechanisms in the single crystal samples were identified, and the permittivity/temperature dependence was also shown to be self‐consistent with the nature of a first‐order ferroelectric phase transition. The primary, low temperature, conduction mechanism in acceptor‐doped BaTiO₃ was determined to be dominated by the migration of oxygen vacancies. The activation energy for oxygen vacancy migration was experimentally determined to have a value of nearly 0.7 eV. This activation energy represents an intrinsic value for vacancy hopping and confirms our previous work that revealed minimal interaction between acceptor dopants and oxygen vacancies in BaTiO₃ in contrast to the well‐documented evidence of defect association in SrTiO₃.     

Preparation,Crystal Structure and Explosive Properties of Copper(II) Perchlorate Complex with 4‐Amino‐1,2,4‐Triazole and Water

A complex from copper(II) perchlorate with 4‐amino‐1,2,4‐triazole (4‐AT, C₂H₄N₄) was synthesized, and elemental composition, molecular structure, and explosive properties were determined. To this end, elemental and X‐ray analyses were carried out, sensitivity to mechanical and thermal stimuli was measured, mechanism of thermal decomposition was investigated, and kinetic parameters of decomposition were determined. In the next step measurements of heat of combustion and detonation velocity were performed. Detonation parameters were also calculated. It was stated that the complex has slightly distorted square bipyramidal (4+2) coordination. The four basal bonds are formed by nitrogen atoms of four 4‐AT molecules. The coordination of the metal is completed by two axial oxygen atoms, one of the perchlorate ion, and one of the water molecule. With respect to explosive properties, tetrakis(4‐AT)copper(II) perchlorate monohydrate belongs to the group of sensitive secondary explosives.     

Long‐Term Properties of Butt‐Welded Poly(propylene)

It is still not clear why the long‐term properties of plastic weld seams can only be differentiated by the very expensive medium tensile creep tests. One hypothesis for justifying this is based on the change in the structure of the weld seam surroundings, another cites the consumption of antioxidants and the following ageing in the weld seam area to be responsible for this. Butt‐welded weld seams made of poly(propylene) were systematically produced under different process parameters. Corresponding to the particular hypothesis, these weld seams were then analyzed in various ways to find correlations or to prove one of the hypotheses. Regarding their short‐term weld seam quality, the analyzed weld seams could not be differentiated through short‐term tensile or short‐term bend test. However, the medium tensile creep tests showed significant differences in both time until failure and long‐term weld seam quality. Under long‐term loading, the start of the brittle crack could be detected in most weld seams in the fine spherulite‐zone or between this zone and the area of the flow lines. This demonstrated again that only long‐term tests are suitable for examining different weld seam qualities. Depending on the welding parameters, times until failure decline with increasing heated‐tool temperature and heating time. Though these parameters lead to a higher consumption of antioxidants in the weld seam, a degradation was not detected in the breaking area. In fact, increasing heated‐tool temperatures and heating times, as well as higher joining pressures lead to a change in the internal structure of the material. This can be seen in morphological structure analyses in the larger bend of the entire weld seam area. A larger bend, however, correlates with higher residual stresses in the weld seam. In the medium tensile creep tests, these residual stresses as well as the tensile stress in the border region and the compressive stress in the middle are superimposed by the tensile stress resulting from the test stress. Thus a greater bend of the weld seam area and higher residual stresses in the weld seam itself lead to shorter times until failure in medium tensile creep tests.

Schematic representation of the formation of residual stresses in a weld seam and residual stresses in the different bended weld seam areas.     

Crystal phase of poly(vinylidene fluoride‐co‐trifluoroethylene) synthesized via hydrogenation of poly(vinylidene fluoride‐co‐chlorotrifluoroethylene)

Trifluoroethylene addition and thermal treatment induced crystal phase transition in a series of poly(vinylidene fluoride‐co‐trifluoroethylene) [P(VDF‐co‐TrFE)] containing varied TrFE molar ratio (6, 9, 12, and 20 mol %) prepared from the hydrogenation of poly(vinylidene fluoride‐co‐chlorotrifluoroethylene have been investigated by means of Fourier transform infrared spectral (FTIR), X‐ray diffraction (XRD), and differential scanning calorimetry (DSC) analyses. The comprehensive applications of the three techniques could distinguish α, β and γ phase of P(VDF‐co‐TrFE) very well. The multipeak fitting technique of DSC is successfully applied to calculate the percentage of different phases in the samples, which allows us to investigate the phase transition process of P(VDF‐co‐TrFE) precisely. It is found that the crystal phase of P(VDF‐co‐TrFE) films is turned from α + γ phase (6 mol % TrFE) to α + γ + β phase (9 and 12 mol % TrFE) to β phase (20 mol % TrFE) at high temperature, and from α + γ phase (6 mol % TrFE) to γ + β phase (9 mol % TrFE) to β phase (>12 mol % TrFE) at low fabricated temperature. Both the fabrication conditions and TrFE addition are responsible for the crystal phase transition of the hydrogenised P(VDF‐co‐TrFE). © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Direct ink writing of aluminium oxynitride (AlON) transparent ceramics from water-based slurries

In this study, transparent AlON ceramics were fabricated via the direct ink writing (DIW) method from the water-based ceramic slurry. The solids loading of the ceramic slurry was optimised by changing the dispersant content, and the printability and water content were then adjusted by adding hydroxyethyl cellulose (HEC). The structure of the green body was complete and no impurity phases were detected. The effects of sintering temperature and dwell time on the bulk density, phase evolution, microstructure, in-line transmittance, and mechanical properties of the ceramics were studied systematically. High optical and mechanical properties of 10 × 10 × 0.9 mm³ single-phase AlON ceramic tiles were obtained by sintering at 1960 °C for 10 h in a nitrogen atmosphere: in-line transmittance of 81.90% at a wavelength of 780 nm, fracture toughness of 1.74 MPa·m^1/2 (2.94 N), and Vickers hardness of 18.56 GPa (2.94 N). This study provides a novel method for synthesising AlON transparent ceramics from water-based ceramic slurries.