Gallium Nitride nano-particles (GaN NPs) are synthesized by a simple nitridation method. A mixture of commercially available β-Gallium Oxide (β-Ga2O3) and GaN powders with about 5 µm particle size was heated at temperatures ranging from 700–1,000 °C in an ammonia (NH3) atmosphere for 1 h. In the powder mixture, the β-Ga2O3 particles converted to GaN NPs agglomerates, while the GaN particles are slightly grown. When the mixture was heated in the NH3 atmosphere at 900 °C, GaN NPs varying from 30 to 50 nm and microsized GaN particles were obtained.
The effect of the lithium ion coexistence on the fluorescent properties was studied for a partially Ag-exchanged LTA (A-type) zeolite. A series of Ag–Li-LTA zeolite samples was prepared by mixing the LTA zeolite powder (1.0 g) with aqueous solutions (100 mL) containing AgNO3 (0.5 mmol) and various amounts of LiNO3 (0–100 mmol). Although the fluorescence intensity was hardly observed in the unheated state for the Ag-LTA and the Ag–Li-LTA zeolites, the intensity was enhanced by the heat-treatment and showed the maximum value for the samples heated at 600 °C. A dramatic enhancement in the fluorescence intensity was observed by increasing the amount of the Li addition with a heat treatment at 600 °C. The highest fluorescent intensity was reached for the Ag(2.8%)–Li(72.6%)-LTA zeolite doped using the solution containing 0.5 mmol/g AgNO3 and 100 mmol/g LiNO3. Furthermore, the fluorescence shifted from a 605 nm (yellow) to the shorter wavelength of 505 nm (green) with the increasing Li amount. The fluorescent intensity due to the coexisting lithium ion for the Ag-exchanged LTA zeolite was significantly superior to those of the Ag–Li-FAU(X- and Y-types) zeolites.
The NH3 nitriding process of TiSi2 micrometer-sized powders were investigated in this paper. TiSi2 powders were heat-treated under NH3 flow in a temperature range of 1,100 to 1,300 °C. The composition and morphology of the resulting composites were characterized by X-ray powder diffraction, scanning electron microscopy with energy-dispersive X-ray spectroscopy, and transmission electron microscopy. Under NH3 flow, TiSi2 grains were first transformed into TiN and Si. Subsequently, Si was transformed into Si3N4 and SiO2 fibers. From this process, mixed materials comprising TiN particles with Si3N4 fibers were obtained.
High-purity mullite ceramics are fabricated to improve their high-temperature mechanical properties using an intelligent eco-friendly sintering process with a transient silica-rich liquid phase formed during sintering, followed by the crystallization of the residual glassy phase of SiO2. The fabricated ceramics possess high density and excellent high-temperature flexural strength. The sinterability of the mullite ceramics improved dramatically when silica-rich compositions were used. This can be attributed to the viscous flow of the silica-rich viscous liquid phase formed during sintering at high temperatures. To increase the high-temperature flexural strength without degrading the fracture toughness, the residual boundary phase was crystallized into cristobalite by controlling its amount and size. The crystallite size of the precipitated cristobalite obtained using suitable post-annealing conditions, i.e., at 1500 °C for 120 h or more, was suppressed; very fine crystals of size 33–38 nm were obtained. The flexural strength measured at 1400 °C for the specimens, which were post-annealed at 1500 °C for 120 h, exceeded that of the as-sintered specimen without resulting in any degradation in fracture toughness at room temperature. These results suggest that suitable grain boundary design conditions, including the composition and post-annealing conditions, can improve the sinterability and high-temperature mechanical properties of the highly pure mullite ceramics at low sintering temperatures. Such grain boundary design can lead to the development of eco-friendly processing of low-temperature sintering for high-performance structural ceramics.
Based on previously reported studies, yttria stabilized zirconia [Y0.15Zr0.85O1.93 (YSZ)] has been used as an epitaxial buffer layer on Si(001) substrates. However, a considerable lattice mismatch exists between the YSZ and Si (−5.4 %). This work elucidates the reported relationship between the lattice parameter and composition of neodymia stabilized zirconia [(NdXZr1−XO2−X/2) (NdSZ)]. According to the relation, the lattice parameter of NdSZ is the same as that of Si at x = 0.75. Therefore, if the epitaxial growth of NdSZ thin film with x = 0.75 is realized on a Si(001) substrate, then zero lattice mismatch can be expected. The deposition of NdSZ thin film on Si(001) substrate was done by dynamic aurora pulsed laser deposition (PLD). Results show that cube-on-cube epitaxial growth (NdSZ(001)//Si(001)) is realized between x = 0.16 and x = 0.52. The best composition of epitaxial NdSZ thin film is regarded as x = 0.47 from the point of crystallinity, orientation and lattice mismatch (−1.1 %). When composition x is larger than x = 0.57, the NdSZ thin film orientation becomes (111). Results also show that the lattice parameter of the NdSZ thin film is larger than that of NdSZ bulk. For x = 0.47 thin film, the coexistence of the epitaxial (221) domains is detected in addition to the (001) cube-on-cube domain. The (221) domain is formed due to lattice matching of the oxygen sub-lattice, which has an isosceles triangle shape. We produced cube-on-cube epitaxial NdSZ thin film on Si(001) substrate with a very small lattice mismatch. However, such a small lattice mismatch brings about additional (221) domains that have been reported in the epitaxial growth of CoSi2 thin film on Si(001) substrate. The lattice mismatch between CoSi2 and Si is −1.2 %, which is approximately equal to that between NdSZ (x = 0.47) and Si.
Garnet-type Li-ion conductor Li6.75(La1−xSmx)3Zr1.75Ta0.25O12 powders were synthesized with 0 ≤ x ≤ 1 using solid-state reaction method. Almost single-phased garnet phase was obtained by synthesis at 900 °C for all Sm contents. The lattice parameters decrease linearly, concomitantly with increasing Sm content, following Vegard’s law. Results of X-ray diffraction and Raman spectroscopy show that Sm is substituted to the rare-earth element site and that the cubic structure of garnet is stable as a main phase at room temperature. Therefore, this study demonstrates that Sm substitution to La site in the garnet-type Li-ion conductor provides continuous lattice parameter control in a wide range up to a = 1.27170(8) nm. It is noteworthy that the wavenumber shifts of Raman mode related to the four-coordinated Li–O bond are observed only slightly in spite of the large lattice constriction and clear observation of peak-top shifts of other cation-oxygen modes, implying that Li-ion conductivity would be less affected by aliovalent substitution to the rare-earth site.
Among many analyzing methods for thin films, atomic force microscopy (AFM) is one of a most powerful tool which enables to analyze local properties as well as microstructure observation in nm scale, but generally it is only applied to the surface of the films and not to the cross section of the films. One of a main reason preventing the cross sectional AFM analysis will be a difficulty in preparation of a flat cross section. In the present study, the authors demonstrate a novel method for obtaining a flat cross section of stacked films deposited on substrate, i.e. perforation fracture method, where preliminary prepared pits by focused ion beam (FIB) on the film surface promote controlled crack propagation and flat cross section of the film is obtained. As a practical example, preparation of cross section and AFM observation for a BT/LNO film deposited on a Pt/Ti/SiO2/Si substrate is introduced.
InGaN-LED-driven solid-state lighting [i.e., white light-emitting diodes (wLEDs)] is now penetrating to our daily life and replacing traditional lighting sources rapidly owing to its energy-saving, high efficiency and environment friendly. Phosphors play key roles in improving the color rendition/gamut, luminous efficiency and lifetime of wLEDs, but the traditional ones for lamps usually do not meet the requirements for wLEDs. This triggers the search for new phosphors that can be excited by blue- or near ultraviolet LEDs. Sialon-based nitride phosphors are emerged as a new family of luminescent materials, superior to oxide or sulfide counterparts in terms of high conversion efficiency, small Stokes shift, excellent chemical and thermal stability. In this mini review, nitride phosphors will be introduced, including their classification, photoluminescence properties, structure-property relations, and applications in general illumination and backlighting.
Ceramics are traditionally synthesized using high temperature annealing. However, cold crystallization is studied with respect to energy saving, low environmental impact, low cost, and hybridization with organic materials and metals, etc. In addition, nanostructure control is required for higher functionality. In this paper, crystal growth control in aqueous solution and morphology control of the ceramic nanostructures are introduced to provide next-generation devices.
In this article, two techniques are described that can enhance the performance of ceramics. First, magnetic field orientation, a technique used to control the particle-assembled structure before sintering, is reviewed using c-axis Si3N4 ceramics as an example. Second, nondestructive internal structure observation based on optical coherence tomography (OCT) is reviewed as a novel evaluation technique using Al2O3 ceramics as an example.
Next-generation ceramic devices will have to be fabricated by novel sintering techniques if they are to obtain the requisite properties such as lightness, robustness, and flexibility. To bind with polymer materials, ceramics must be sintered at temperatures of under 300 °C. In this study we developed a number of low-temperature sintering techniques to synthesize complex oxides by exploiting the chemical reactions among the raw material components. We also developed a number of novel low-temperature synthesis processes to utilize the aforesaid synthesis reactions in sintering. Complex oxides can be prepared at low-temperature using hydroxide and peroxide raw materials. Notably, we found that perovskite oxides, including alkaline earth oxides, can be prepared at temperatures below 100 °C using hydroxide raw materials. (Ba,Sr)(Co,Fe)O3 can be sintered as a cathode material on solid oxide fuel cells at 700 °C by reactive sintering using the solid state synthesis reaction among the peroxide-and-hydroxide mixtures. Cells produced by this method show superior electrochemical performance attributable to an improved interface on the cathode layer derived from reactive sintering. We also found that the novel low-temperature synthesis method effectively yields bulk bodies of perovskite materials such as BaZrO3 at temperatures below 100 °C in atmospheric pressure.
The CaSmAlO4-doped 0.84CaTiO3–0.16Sm0.9Nd0.1AlO3 ceramics with permittivity around 62 were prepared using a conventional solid-state reaction method. The relationship between their structures and microwave dielectric properties was explored by X-ray diffraction, Raman spectroscopy and scanning electron microscopy. A suitable amount of CaSmAlO4 addition is beneficial for improving the Q×f value and tuning τf concurrently. However, excess amount of CaSmAlO4 generated secondary phase and deteriorated the Q×f value. The 0.5 mol % CaSmAlO4-doped 0.84CaTiO3–0.16Sm0.9Nd0.1AlO3 ceramics exhibited the best performance of εr = 62.3, Q×f = 38400 GHz and τf = +49.5 ppm/°C sintered at 1400 °C for 6 h. Although the temperature stability needs to be made better, the CaSmAlO4-doped 0.84CaTiO3–0.16Sm0.9Nd0.1AlO3 ceramics pave the way to develop a promising candidate for 5G dielectric resonators with medium-high permittivity (60 < εr < 70).
In this study, solid solutions of double-perovskite-type LixLa(1−x)/3Nb1−yTayO3 (x = 0.1, y = 0.0–1.0) were synthesized by solid-state reaction. We successfully prepared tetragonal Li0.1La0.3Nb1−yTayO3 single phases by increasing the reaction temperature and the Ta composition. The lattice constants of Li0.1La0.3Nb1−yTayO3 were observed to increase with increasing Ta composition, and densified Li0.1La0.3Nb1−yTayO3 pellets composed of larger grains than Li0.1La0.3NbO3 and Li0.1La0.3TaO3 were obtained. The relationship between the Nb–Ta solid solution in Li0.1La0.3Nb1−yTayO3 and ionic conductivity was investigated, which revealed that Li0.1La0.3Nb1−yTayO3 (y = 0.2) exhibited maximum ionic conductivity (σ = 7.78 × 10−5 S cm−1) at room temperature and that ionic conductivity decreased with increasing Ta composition. The activation energies of Li0.1La0.3Nb1−yTayO3 were found to be 0.34–0.38 eV and increased with increasing Ta composition.
Bi0.5Na0.5TiO3-based materials have drawn much attention as a lead-free ferroelectric and piezoelectric materials. We focused on Bi0.5Na0.5TiO3–NaNbO3 and Bi0.5Na0.5TiO3–NaTaO3 solid solutions, which can be denoted as (Bi0.5(1−x)Na0.5(1+x))(Ti1−xMx)O3 (M = Nb, Ta, x = 0.025, 0.05), and then investigated their ferroelectric and piezoelectric properties, and crystal structures using quantum beam. It was found that the ferroelectric and piezoelectric properties were deteriorated by the Nb and Ta substitutions with x = 0.05. Since the crystal structure analysis on the as-synthesized samples could not explain the change in the ferroelectric and piezoelectric properties, we analyzed the crystal structure of the samples after a polarization. It was indicated that the tilting angle of adjacent (Ti,M)O6 increased significantly only in the case of Bi0.5Na0.5TiO3, the Nb- and Ta-substituted samples with x = 0.025. It was considered that the crystal structure after the polarization played an important role for the ferroelectric and piezoelectric properties.
Solutions derived by cosolvent-free (solventless) acid-catalyzed hydrolytic polycondensation of tetramethoxysilane (TMOS)–water and tetraethoxysilane (TEOS)–water binary systems were used to form silica films by dip-coating. Reactions in these solutions were examined by liquid-state 1H and 29Si nuclear magnetic resonance (NMR) spectroscopy, and the results were quantitatively analyzed based on a general reaction formula of tetraalkoxysilane deduced in this study. Transparent crack-free sintered silica films as thick as ∼500 nm were obtained from the TEOS-based solutions aged at 80 °C, and similar films were also prepared from solutions stored for 30 d at room temperature. Water molecules were nearly absent both in the TMOS and TEOS systems. Unreacted SiOH groups were depressed in the TMOS system whereas abundant in the TEOS system. These SiOH groups in the TEOS system are essential in producing uniform thin films as they render silica oligomers hydrophilic to increase affinity to glass substrates. Furthermore, they were inert and their slow polycondensation enables the extension of pot life. Films prepared from the TMOS system were non-uniform and cracked because the lack of residual SiOH groups impaired wettability to glass substrates and permitted the shrinkage of deposited liquid films before consolidation.
Inspired by biomineralization in nature which provides the formation of various inorganic minerals under mild temperatures and pressures conditions, we report here the low-temperature mineralization sintering process (LMSP) of SiO2–CaO–P2O5 bioactive glass nanoparticles (BGNs). The ternary BGNs were successfully synthesized by an alkali mediated sol–gel method. The obtained glass nanoparticles, having around 30 nm in diameter, were sintered in a mold under an applied pressure of 300 MPa at 120 °C with an aid of small amount of simulated body fluid (SBF) solution. Under the condition, BGNs were densified through biomineralization with a formation of amorphous calcium phosphate phase which filled up the interparticle boundaries and bonded each glass nanoparticles. The relative density and Vickers hardness of the sintered BGNs were sufficiently high, 86 % and 2.09 GPa, respectively, although the low sintering temperature. These values were higher than those of BGNs sintered by the same procedure with no aqueous solution (57 %, 0.68 GPa), distilled water (77 %, 1.52 GPa), and even the conventionally sintered BGNs at 550 °C (69 %, 0.93 GPa) and 850 °C (81 %, 2.02 GPa). These results suggest that the LMSP is a promising and cost-effective process for obtaining bioactive glass and ceramic bulk materials at low temperature.
This study investigated the synergistic effect that the co-doping of cobalt and copper elements has on Jun porcelain glazes. The phase composition of the glazes was analyzed using X-ray diffraction (XRD). The sample morphology and phase separation structure of the glazes were examined using field emission scanning electron microscopy (FESEM). The element composition and valence state of the glazes were analyzed using X-ray photoelectron spectroscopy (XPS). The element distribution of the glazes was studied using an energy dispersive spectrometer (EDS). Our research shows that the distribution of the Co and Cu elements in the glaze layer is random, and indicates the presence of a liquid–liquid phase separation structure in the glazes. The coloring of the glazes is primarily related to the content of the cobalt and copper elements, the valence state of the coloring ions, and the micro-morphology. Additionally, there is an obvious synergistic effect between the coloring metal elements Co and Cu.
The local structure of WOx clusters modified on Ti-doped hydroxyapatite (Ti-HAp) photocatalyst surface was analyzed using X-ray absorption fine structure (XAFS) measurements. W L1- and L3-edge X-ray absorption near-edge structure (XANES) spectra analyses revealed that WOx clusters include WO4 and WO6 structures and that WO6 amounts increase concomitantly with increasing WOx cluster amounts. Results of analyses of W L3-edge extended X-ray absorption fine structure (EXAFS) spectra confirmed this finding, demonstrating that the average coordination number of W surrounded by O increases from 4 to 5 with increasing WOx cluster amount. The number of W–O–W bonds increased concomitantly with increasing amounts of modified WOx clusters, indicating the formation of WOx cluster aggregates. Assuming that two-dimensional WOx monolayer domains were formed and that the domain is square, the average WOx cluster structure was calculated as changing from a monomeric to a trimeric or tetrameric structure with increasing WOx loading amount. The cluster size obtained from the model is consistent with those found in our earlier experimental study. The cluster structure represented here demonstrated that the modified WOx clusters included a low coordination structure. Its electronic structure became different from that of doped W or bulk WO3 and a suitable electron transition path from Ti 3d to W 5d was created, showing high photocatalytic activity.
Perovskite solutions with potassium (K) and formamidinium (FA) iodides added were used to fabricate perovskite solar cells. Since the lattice constants increased with the addition of FA, the substitution by FA of the CH3NH3 (MA) site of the perovskite crystal was confirmed. In addition, conversion efficiencies were improved for devices with K and FA added compared with standard devices. The presence of K in the perovskite solution promoted formation of highly (002)-oriented crystals, which decreased the lattice strain of perovskite crystals. Filling the MA defect sites with K and FA can prevent the recombination of electrons and holes and improve the photovoltaic characteristics.
Foam ceramic materials with uniform pore structure were prepared by adopting organic foam impregnation method using mullite (0.045–0.075 mm) extracted from fly ash as raw materials, aluminum dihydrogen phosphate and kaolin (0.045–0.088 mm) as bonding reagent and plasticizer, respectively. The influence of phosphate content, solid (mullite and kaolin) content and ball-milling time on performance of mullite slurry has been investigated. Especially, the relationship between various properties of the slurry and obtained foam ceramics have been discussed. Furthermore, the physical properties and sintering behaviors of the as-prepared samples at different temperatures were systematically investigated. The result indicated that a high-quality slurry with low sedimentation degree, suitable viscosity and small particle D50 can be prepared under the condition of phosphate content of 12.5 mass %, solid phase content of 62 mass % and ball milling time of 8 h. Finally, the mullite foam ceramic products with a compressive strength of 1.62 MPa, an apparent porosity of 87 % and a thermal shock resistance of 13 times were prepared after sintering at 1450 °C for 4 h.
The “K2O–Na2O” binary and “K2O–Na2O–Li2O” ternary flux systems on the densification behaviors of the porcelain building ceramic were analyzed. The results showed that when K2O and Na2O content were equivalently replaced by Li2O content, the sintering temperature of “K2O–Na2O–Li2O” flux samples was reduced to 1090–1130 °C, which is lower than that of “K2O–Na2O” binary flux sample (1130–1160 °C). The corresponding sintering temperature range of the ternary flux sample is widened from 30 to 40 °C, and thus the bending strength of the ternary flux sample is increased by 3.5 %. energy spectrometer system and “K2O–Na2O–Li2O” ternary frit simulation results indicate ternary flux sample has more Al2O3 and SiO2 content in glass phase than those of the binary flux sample, however, the alkaline oxide contents are higher than those of ternary flux sample. For binary flux samples, “K2O–Na2O” fluxes melt themselves due to low melting point and thus suddenly appear a large amount of the liquid phase and have no time to dissolve Al2O3 and SiO2 contents, resulting in low glassy viscosity of the sample. However, when Li2O content equivalently replace K2O and Na2O contents for the ternary flux sample, they would appear high glassy viscosity steeply, due to the formation of low eutectic mixture melted with high Al2O3 and SiO2 contents. Combined with X-ray powder diffraction patterns and scanning electron microscope images, the ternary flux samples have more crystallite phase, smaller porosity and pore size than those of binary flux samples. Therefore, the properties of the ternary flux samples are superior to those of binary flux samples.
This study developed phase-field method (PFM) technique in oxide melt system by using a new mobility coefficient (L). The crystal growth rates (v0) obtained by the PFM calculation with the constant L were comparable to the thermodynamic driving force in normal growth model. The temperature dependence of the L was determined from the experimental crystal growth rates and the v0. Using the determined L, the crystal growth rates (v) in alkali disilicate glasses, Li2O–2SiO2, Na2O–2SiO2 and K2O–2SiO2 were simulated. The temperature dependence of the v was qualitatively and quantitatively so similar that the PFM calculation results demonstrated the validity of the L. Especially, the v obtained by the PFM calculation appeared the rapid increase just below the thermodynamic melting point (Tm) and the steep peak at around Tm–100K. Additionally, as the temperature decreased, the v apparently approached zero ms−1, which is limited by the L representing the interface jump process. Furthermore, we implemented the PFM calculation for the variation of the parameter B in the L. As the B increased from zero to two, the peak of the v became steeper and the peak temperature of the v shifted to the high temperature side. The parameters A and B in the L increased exponentially and decreased linearly as the atomic number of the alkali metal increased due to the ionic potential, respectively. This calculation revealed that the A and B in the L were close and reasonable for each other.
We have prepared a multicomponent glass, in which photocatalytic Bi2O3–Nb2O5 and Bi2O3–SiO2 phases are crystallizable, and have examined the nanometric structure and photocatalytic activity in the resulting glass-ceramics (GCs). The GCs crystallized the Bi3NbO7 nanophase followed by the Bi5Nb3O15 nanophase as increasing the heat-treatment temperature, and eventually, the nano-sized Bi5Nb3O15–Bi4Si3O12 co-crystallized GC sample was obtained. Although photocatalytic activity was confirmed in the singly Bi3NbO7-/Bi5Nb3O15-crystallized samples by means of the degradation test of rhodamine B dye, a higher activity was found in the co-crystallized sample. The high photocatalytic activity was considered in accordance with a nanometric structural observation.
The crystal structure of Ca(Fe3+0.4Si0.6)O2.8 oxygen-deficient perovskite phase synthesized at 12 GPa and 1400 °C was studied using synchrotron powder X-ray diffraction. The phase is isostructural to low-pressure phase of Ca(Al0.4Si0.6)O2.8. The structure was refined by the Rietveld method and is consists of a perovskite-like triple-layer of corner-shared (Fe3+,Si)O6 octahedra and a double-layer of SiO4 tetrahedra those are stacked alternatively in the  direction of ideal cubic perovskite. Small degree of Fe3+/Si disorder was detected between two octahedral sites. The structure is compared with other oxygen-deficient perovskites.