Structures containing stacked layers of silicon-rich silicon nitride (green-blue luminescence) and oxide (red luminescence) fabricated by ion implantation are reported, and it is shown how a Si-based material can be engineered to emit over a broad range. To study in depth the emission from implanted SiNx matrices, single nitride layers have been also fabricated by the first time. Si excess variation and the relative thickness of nitride and oxide provide the intensity and position variation of the peaks, and thus open the way to engineer a stack with desired emission properties over the whole visible spectrum.

Herein we compare the lattice parameters, room temperature shear and Young’s moduli, and phonon thermal conductivities of Ti2AlC0.5N0.5 and Ti3Al(C0.5, N0.5)2 solid solutions with those of their end members, namely Ti2AlC, Ti2AlN, Ti3AlC2, and Ti4AlN2.9. In general, the replacement of C by N decreases the unit cell volumes and increases the elastic moduli and phonon thermal conductivities. The increase in the latter two properties, however, is sensitive to the concentrations of defects, most likely vacancies on one or more of the sublattices.

We conducted an investigation into the thermodynamic properties of two stoichiometric CaCu3Ti4O12(CCTO) samples prepared by solid-state reaction and soft chemistry methods to probe the stability of the material relative to simpler oxide constituents (e.g., CaO, CuO, and TiO2) over a wide temperature range. Thermodynamic functions (i.e., heat capacity, formation enthalpies, entropies, and Gibbs free energies) have been measured from near absolute zero to 1100 K using calorimetric methods, including drop solution, low-temperature adiabatic relaxation, and differential scanning calorimetry. In addition, the thermodynamic characteristics of the magnetic-phase transition from the antiferromagnetic to the paramagnetic state are reported. It has been shown that CCTO is very stable relative to constituent oxides and calcium titanate at room temperature and higher, independent of the synthesis route. The enthalpic factor is dominant in the thermodynamics of CCTO, with the entropic factor having almost no effect on the stability of the compound relative to other oxide assemblages. The recommended values for the standard molar enthalpy of formation from constituent oxides and from elements at 298.15 K are −122.1 ± 4.5 and −4155.7 ± 5.2 kJ/mol−1, respectively. The mean of the third law entropy at 298.15 K is 368.4 ± 0.1 J/mol−1/K−1. Based on the thermodynamic data reported, the study confirms the possibility of CCTO decomposition in a reducing atmosphere or CO2 under conditions recently observed in experiments.

In this article, we describe oxidation of molten Sn–0.07 wt% P alloy exposed in air at 280 °C. Although oxidation can be effectively reduced by the addition of trace phosphorus, the oxide film has a poor protection for the molten alloy with a high P concentration. The oxide film was analyzed by x-ray photoelectron spectroscopy. Comparing the results with the low P sample, there was a high phosphorous content in the film and a new Sn–P compound on the surface of the high P sample. It is assumed that the poor protection against oxidation of the film could be due to volatility of phosphorus in the Sn–P alloy at the temperature.

In this article, we present the vacuum ultraviolet-visible spectroscopic properties of NaRFPO4:Tb3+ (R = Gd and Y). Because the samples show intensive absorption near 172 nm and bright emission, the composition of the phosphors has been further optimized and an ideal phosphor NaGd0.3Y0.5Tb0.2FPO4 is obtained. This phosphor exhibits favorable characteristics such as a lower preparation temperature, an intensive emission under 172-nm excitation, a shorter decay time (τ1/10 = 8.7 ms) in comparison with the commercial green plasma display panel (PDP) phosphor Zn2SiO4:Mn2+ (τ1/10 = 10.8 ms), a good thermal stability for luminescence performance, and a uniform particle size around 2.3 μm. Hence, the phosphor NaGd0.3Y0.5Tb0.2FPO4 can be considered a promising green phosphor for use in PDPs.

Bulk metallic glass (BMG) formations in Co- and Fe-based alloy systems are investigated by using our cluster line approach in combination with minor alloying principle. Basic ternary alloy compositions in Co–B–Si, Fe–B–Y, and Fe–B–Si systems are first determined by cluster lines defined by linking special binary clusters to third elements. Then the basic ternary alloys are further minor alloyed with 3 to 5 at.% Nb to improve glass-forming abilities (GFAs) and ϕ3 mm BMGs are formed in (Co8B3–Si)–Nb and (Fe8B3–Y)–Nb but not in (Fe8B3–Si)–Nb, TM8B3 (TM = Fe, Co) being the most compact binary cluster. The BMGs are expressed approximately with a unified simple composition formula: (TM8B3)1M1, M = (Si, Nb) or (Y, Nb). Finally, mutual Fe and Co substitutions further improve the GFAs as well as the soft magnetic properties, e.g., Is reaching 0.98 T and Hc < 6 A/m for the Co–Fe–B–Si–Nb BMGs. Using the (cluster)1(glue atom)1 model, a new ternary BMG Fe8B3Nb1 is obtained.

MgTe2O5 ceramics were prepared by solid-state route. These materials were sintered in the temperature range of 640–720 °C. The structure and microstructure of the compound was investigated using x-ray diffraction (XRD), Fourier transform infrared (FTIR), Raman spectroscopy, and scanning electron microscopy (SEM) techniques. The dielectric properties of the ceramics were studied in the frequency range 4–6 GHz. The MgTe2O5 ceramics have a dielectric constant (ϵr) of 10.5, quality factors (Qu × f) of 61000 at 5.3 GHz, and temperature coefficient of resonant frequency (τf) of −45 ppm/°C at the optimized sintering temperature of 700 °C. The microwave dielectric properties of these materials at cryogenic temperatures were also investigated.

A viscoelastic solid was contacted by a pointed indenter using low-frequency large-amplitude sinusoidal load functions to determine its contact stiffness in a manner similar to that of the continuous stiffness measurement (CSM) technique but in a quasi-static condition. The contact stiffness of a viscoelastic solid determined by the CSM technique, or the dynamic stiffness, is known, from previous CSM-based studies, to overestimate the quasi-static contact stiffness. The contact stiffness of a viscoelastic solid determined in a quasi-static manner is thus hypothesized to help predict the contact depth more accurately. A new analysis procedure based on truncated Fourier series fitting was developed specifically to process the large amplitude sinusoidal indentation data. The elastic modulus of the material characterized in this work was in agreement with that determined by dynamic mechanical analysis, thereby providing evidence for the validity of the present method in characterizing other viscoelastic materials.

Experimental studies were conducted to investigate the microwave (MW) heating behavior of soda-lime glass beads with added iron powder. These studies were intended to obtain fundamental knowledge for vitrification solidification and for the fabrication of metal-reinforced glass-matrix composites. The glass beads (0.2 mm diameter) did not heat very well by themselves at temperatures greater than 200 °C within 600 s in a multimode applicator at a power of 0.67 W. The addition of iron powder (average 70 μm, volume fraction 18%) made it possible to heat the glass beads above 700 °C within 60 s. At lower fractions of 3–11 vol%, however, a sudden temperature rise [thermal runaway (TRW)] occurred after the incubation time period. A single-mode MW applicator was used for clarifying the electric (E)-field and magnetic (H)-field contributions to the heating of each material and their mixtures. The results of this study demonstrated that the H-field contributed to the heating of the iron and then triggered the heating of the glass. The E-field component is necessary for heating the glass to a temperature higher than 800 °C. The factors determining the threshold values of the volume fraction causing TRW are discussed.

The mechanical properties and corresponding microstructure development of the AZ31 Mg alloy after treatment with equal channel angular pressing (ECAP) and subsequent electropulsing (ECP) was investigated. Comparing the ECAP+ECP-treated AZ31 alloy with the ECAP-treated alloy, the elongation to failure was improved significantly, while the yield stress and the ultimate tensile strength were not decreased, the grain sizes were slightly increased and more homogeneous, and the texture was barely changed. The main mechanism for the evolution of the structures and properties might be ascribed to the increased nucleation rate on recrystallization and the decreased dislocation density during the ECP treatment. It was reasonable to expect that the ECAP+ECP treatment would provide a promising approach for enhancing the mechanical properties of the Mg alloys.

There is often a tradeoff between strength and ductility, and the low ductility of ultrafine-grained (UFG) materials has been a major obstacle to their practical structural applications despite their high strength. In this study, we have achieved a ∼40% tensile ductility while increasing the yield strength of FeCrNiMn steel by an order of magnitude via grain refinement and deformation-induced martensitic phase transformation. The strain-rate effect on the inhomogeneous deformation behavior and phase transformation was studied in detail.

New porous biomaterials based on hydroxyapatite (HAp) were designed as obturation materials for dental cavities. Synthetic HAp powder with a particle diameter of 150 μm was agglutinated using three different polyurethane monocomponents (rigid, semi-rigid, and flexible), enabling the matching of their properties to those of real teeth. Alumina particles were also added in some cases. Our new hybrid materials contain up to 60% HAp. Interconnected pores range in size from 100 to 350 μm, while the pore volume fraction varies between 25% and 60%. Most of these materials possess the right morphology for implants and prostheses because their porous structures can be vascularized for bone and tooth ingrowth. Some samples also contain alumina particles to improve the abrasion resistance and to support the stresses produced during mastication. The materials were characterized by x-ray diffraction, scanning electron microscopy, and mechanical testing, along with abrasion, scratch, sliding wear, friction, and staining tests.

The molecular dynamics method has been used to simulate mode I cracking in Ni3Al. Close attention has been paid to the process of atomic configuration evolution of the cracks. The simulation results show that at low temperature, the Shockley partial dislocations are emitted before the initiation of the crack propagation, subsequently forming the pseudo-twins on (111) planes in crack-tip zone, and then the crack cleavage occurs. The emitting of the Shockley partial dislocations accompanies the crack cleavage during the simulation process. At the higher temperature, the blunting at the crack tip is caused by the [110] superdislocations emitted on (100) plane. The present work also shows that the dipole dislocations on (111) planes in the 1/2[110] dislocation core can be formed.

Dynamic indentation techniques are often used to determine mechanical properties as a function of depth by continuously measuring the stiffness of a material. The dynamics are used by superimposing an oscillation on top of the monotonic loading. Of interest was how the oscillation affects the measured mechanical properties when compared to a quasi-static indent run at the same loading conditions as a dynamic. Single crystals of nickel and NaCl as well as a polycrystalline nickel sample and amorphous fused quartz and polycarbonate have all been studied. With respect to dynamic oscillations, the result is a decrease of the load at the same displacement and thus lower measured hardness values of the ductile crystalline materials. It has also been found that the first 100 nm of displacement are the most affected by the oscillating tip, an important length scale for testing thin films, nanopillars, and nanoparticles.

The current study revealed the effects of strain rate on tensile strength and ductile-to-brittle transition of Sn–3Cu/Cu joints in the strain rate range of 4.2 × 10−5 to 2.4 × 10−1 s−1. Experimental results indicate that these joints broke in a ductile manner at low strain rates with a rapid increase in the tensile strength but displayed a brittle manner at higher strain rates with a slow increase in the tensile strength, indicating a typical ductile-to-brittle transition feature. A method was proposed to estimate the interfacial strength between the solder and the intermetallic compounds.

A series of novel epoxy/clay nanocomposites (EPOCg-x) were prepared with a selected epoxy resin and x wt% of a mechanically ground phosphorus-containing organoclay (POCg). The results of x-ray diffraction (XRD), Fourier transform infrared, and field emission scanning electron microscopy measurements showed that POCg was size-reduced, and its silicate layers were disordered by the grinding process. The results of XRD and transmission electron microscopy of the nanocomposites suggested that the POCg particles were well-dispersed in the epoxy matrix with a combination of intercalation and destruction platelet structures. The as-prepared nanocomposites remained thermally stable above 376 °C. Furthermore, the storage modulus in the glass state, surface hardness, char residue, and limiting oxygen index (LOI) of the as-prepared nanocomposite were all significantly increased with increasing the POCg content. The large increment of LOI, 10 units higher than that of neat epoxy, indicated that an extraordinary enhancement on flame retardancy was obtained from EPOCg-5.

The interfacial reactions and ball shear properties of an In–48wt%Sn solder joint with an electroplated Au/Ni ball grid array substrate were investigated with increasing numbers of reflows using scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectrometry, inductively coupled plasma-atomic emission spectroscopy, x-ray diffractometry, and bonding testing. After one reflow, two different intermetallic compound (IMC) layers, AuIn and AuIn2, were formed at the solder–substrate interface. The AuIn was completely transformed into the AuIn2 after three reflows. The AuIn2 IMC layer broke off, and a thin continuous Ni3(SnxIn1–x)4 IMC layer was formed between the molten solder and the exposed Ni substrate after four reflows. After 10 reflows, the AuIn2 IMC layer completely spalled off the substrate and the Ni3(SnxIn1–x)4 IMC layer was dissolved into the molten solder. These interfacial reactions greatly affected the shear properties of the solder joint.

We have investigated structural changes of amorphous borosilicon carbonitride materials with atomic ratios of B/Si/C of 2/3/6 and 4/3/6 calcined at several temperatures. The boron K-edge x-ray absorption spectra showed that the structures of both hexagonal boron nitride ([BN3] unit) with nitrogen-void defects ([BN2] and [BN1] units) and boron oxide existed in the samples, and the relative peak intensity due to the [BN3] unit became stronger by increasing the calcined temperature. It is thought that the well-developed B–N chain and the borosilicate glass coating lead to the high resistance to oxidation at high temperature. X-ray diffraction and infrared measurements followed the x-ray absorption near-edge spectroscopy findings.

This article is focused on a fractography study of cleavage cracking at triple grain boundary junctions in freestanding silicon thin films. At a triple junction, as the crystallographic orientations of the two grains ahead of the crack are different by only a few degrees, the cleavage front advance becomes quite jerky. The crack first enters the grain of smaller boundary toughness and then turns into the other grain from the lateral direction. Consequently, the overall fracture resistance cannot be analyzed in the framework of line-average theory. The nonuniform characteristic of crack behavior can be attributed to the increase in local stress intensity. A few typical crack front advance modes are identified.

The surface enthalpy of ZnO nanoneedles has been measured by oxide melt solution calorimetry of samples with different surface areas. Water adsorption calorimetry was carried out to characterize the stabilization effect of surface hydration. The surface enthalpies of hydrated and anhydrous surfaces (8.21 ± 0.67 and 9.81 ± 0.69 J/m2, respectively) are larger than those of nanorods. The less stable surface of nanoneedles provides a driving force for the transformation of nanoneedles into nanorods during aging. The formation of bushlike assemblies of nanoneedles is also discussed.