Rutile structured TiO₂ has very high dielectric permittivities in non-ferroelectric materials. To understand the reason why rutile TiO₂ has high ionic polarizabilities, it is essential to analyze accurate dielectric spectra of rutile TiO₂ in the THz region. In this study, the complex permittivity of rutile TiO₂ single crystal in the range 30–700 cm⁻¹ (0.90–21 THz) was directly measured using the anisotropic far-infrared spectroscopic ellipsometer. The three E_u modes and one A_2u mode, which are all infrared-active phonon modes in rutile TiO₂, were observed. Moreover, the resonance frequencies of the phonon modes approximately were coincident with a calculation result of first-principles and the analysis data by a harmonic oscillator model. From the examination of the dielectric response, it was found that E_u(1) mode, which indicates the oscillation of Ti ions against O ions in the same phase, was dominant contributor to the static permittivity for a-axis. On the other hand, the high permittivity for c-axis was due to “soft” A_2u mode.

View full abstract

Electronic structure across the metal–insulator (MI) transition of electron-doped V_1−xW_xO₂ epitaxial films (x = 0–0.06) grown on α-Al₂O₃ substrates was studied by means of thermopower (S) measurements. Significant increase of |S|-values accompanied by MI transition was observed, and the transition temperatures of S (T_S) decreased with x in good linear relation with MI transition temperatures. |S| values of V_1−xW_xO₂ films at T > T_S were constant at low values of 23 µV K⁻¹ independently of x, which reflects a metallic electronic structure, whereas, those at T < T_S almost linearly decreased with logarithmic W-concentrations. The gradient of −213 µV K⁻¹ agrees well with −k_B/e·ln10 (−198 µV K⁻¹), suggesting that V_1−xW_xO₂ films have insulating electronic structures with a parabolic density of state around the conduction band bottom.

View full abstract

Ferroelectric ceramic fiber is expected to demonstrate a wide variety of practical applications in industrial fields due to the flexibility and shape anisotropy. Lead-free ferroelectric (Na,K)NbO₃ (NKN) fiber was synthesized through electrospinning method using aqueous-based citrate precursor (CP). The morphology of electrospun fibers was observed and the properties of the precursor solution, such as viscosity, electrical conductivity and evaporation rate, were investigated. Addition of ethanol and acetic acid to the solvent of the PVA solution worked well for the electrospinning since both additives could control the electrical conductivity as well as evaporation rate of the CP/PVA prepared solution. The properties of the precursor, especially electrical conductivity and evaporation rate have significant influence on the morphology and homogeneity of the developed fibers. The homogeneous NKN fibers with a single perovskite structure of orthorhombic phase at room temperature and controllable diameter ranging approximately 100 to 1100 nm were obtained, indicating that the electrospinning of ferroelectric NKN fiber through CP route was successfully conducted.

View full abstract

We designed and fabricated acoustic matching layers made of a BaTiO₃/epoxy 0–3 composite material for a lead-free ultrasonic flowmeter. Specific acoustic impedance of fabricated 0–3 composite was controlled by changing volume fraction of BaTiO₃ fine particles. When the volume fraction of BaTiO₃ fine particles was 40 vol % or less, sufficiently uniform 0–3 composite materials and various specific acoustic impedances of 2.6–6.9 × 10⁶ kg/m²s were obtained. For improving an accuracy of a lead-free ultrasonic transducer with (K,Na)NbO₃-based ceramics, a pair of acoustic matching layers with a specific acoustic impedance of 6.35 × 10⁶ kg/m²s and a thickness of 0.260 mm were fabricated. By using the fabricated acoustic matching layers in a lead-free ultrasonic flowmeter, the amplitude of output voltage was improved by 35% compared to that using commercialized matching layers. Even in comparison with the commercialized ultrasonic flowmeter with PZT-based materials, the amplitude of output voltage with the fabricated composite matching layers was 83.1%. The lead-free ultrasonic flowmeter with the fabricated composite matching layer had high accuracy of a flow rate error of 3.5% or less. From above results, the effectiveness of the optimized composite matching layers was verified.

View full abstract

One-axis-oriented BiFeO₃ (BFO)-based films were fabricated on platinized silicon and SUS 316L substrates using nanosheets of calcium niobate (ns-CN) with pseudo-perovskite crystal structure. Ca₂Nb₃O₁₀ nanosheets (ns-CNs) were supported on the substrates by dip coating, followed by chemical solution deposition (CSD) of Mn-doped BFO (Mn-BFO) films. Preferential crystal growth of (100)-oriented BFO films was achieved on both ns-CN/(111)Pt/TiO₂/(100)Si and ns-CN/(111)Pt/SUS316L substrates. The out-of-plane lattice parameters of the BFO films on ns-CN/(111)Pt/SUS316L were larger than the parameter reported for BFO bulk because of elastic deformation caused by thermal stress between the BFO films and SUS316L substrate, whereas those of the films on ns-CN/(111)Pt/TiO₂/(100)Si were smaller than the reported value. The remanent polarization of the Mn-BFO films was enhanced to approximately 60 µC/cm² on ns-CN/(111)Pt/SUS316L because of the compressive thermal stress that causes elastic elongation of Mn-BFO crystals to align or change the tilt angle of their polar axes for the substrate surface.

View full abstract

Transparent ZnO films were fabricated on glass substrates by a chemical bath deposition method using zinc acetate solutions also containing AlCl₃. A predominant effect of the Al³⁺ addition seemed to be suppression of the growth of ZnO crystals and change of the crystallographic orientation of ZnO films. The c-axis and the a-axis of the ZnO films came to stand parallel and vertical to the substrate, respectively, by increasing the Al³⁺ concentration. A post ultraviolet irradiation to the films led to a decrease in the sheet resistance from the order of 10⁶ to 10⁴ Ω·sq.⁻¹ without changing the morphology or the crystallinity. This might be related to the photocatalytic effect of ZnO to decompose residual organics in the films and increase the number of carriers. The ZnO film obtained from the solution with 1.0 mol % AlCl₃ showed the lowest sheet resistance of 2.5 × 10⁴ Ω·sq.⁻¹.

View full abstract

We have investigated high-temperature dielectric properties of titania nanosheet (Ti_0.87O₂), a new class of high-κ nanomaterials derived from the exfoliation of layered compounds. In-situ characterizations using atomic force microscopy indicate a robust insulating property in a monolayer form of Ti_0.87O₂ nanosheets even at 200°C. Furthermore, layer-by-layer assembled nanocapacitors exhibit both size-free high-ε_r characteristic (~120) and high insulation resistance (~10⁻⁷ A/cm²) at high temperatures up to 250°C. The simultaneous improvement of ε_r and thermal stability in high-κ nanodielectrics is of critical importance for applications of high-temperature capacitors.

View full abstract

Crystal-oriented (Bi_0.5, Na_0.5)_0.85–Ba_0.15TiO₃ (BNBT15) ceramics with a perovskite crystal structure were prepared by colloidal processing in a rotating high magnetic field to improve their piezoelectric properties. The presence of BaTiO₃ leads to anisotropic crystal lattices, allowing crystal-oriented BNBT15 ceramics to be successfully fabricated, using a rotating magnetic field to orient the c- and a-axes of the crystal in the powder compact. The phase transformation that occurred during sintering redistributed the c-axis oriented structure along both the a- and c-axes. Again, the c-axis was enhanced by electrical field polarization. A piezoelectric constant of 122 pC/N was obtained, which is larger than the 88 pC/N of BNBT ceramics.

View full abstract

Silver electrodes were prepared on the silicon wafer surface using the wetness of an alloy liquid phase produced in the sintering process of the silver powder. Tellurium, which forms a low-melting-point alloy with silver, was doped to the silver powder, and the physical and chemical properties of the synthesized tellurium-doped silver powder were investigated. When silver and tellurium powders were mixed to produce a low-melting-point eutectic crystalline mixture with a silver-to-tellurium ratio of 33.0:67.0 (mol %), a rapid mutual diffusion occurred by heating, following which fusion occurred at the eutectic temperature. When tellurium-doped silver paste prepared with a silver-to-tellurium ratio of 98.5:1.5 (mol %) was printed onto a silicon wafer with texture formed on the surface and then sintered, wetting due to a phase which have been a liquid phase during the sintering process was confirmed at the interface between the silver electrodes and wafer. Silicon was dispersed in silver and tellurium in this phase, and physical contacts of a phase composed of silver, tellurium, and silicon were confirmed between the silver electrodes and wafer.

View full abstract

LaNiO₃ cuboid particles were successfully synthesized by the sol–gel method in the presence of molten chlorides. The precursor gels derived from the La(NO₃)₃ and Ni(CH₃COO)₂ solution were heated with molten chloride, NaCl or KCl, above the melting point of respective molten salts. The formation reaction of LaNiO₃ was completed below the melting point of these chlorides, and then crystal growth process might be facilitated in liquid phase provided by the molten chlorides due to an increase in the mass-transportation rate. The formation of the submicron to micron-sized LaNiO₃ cuboid particles, which are enclosed by {100} facets of pseudocubic perovskite, is confirmed by the electron microscope observations and the electron diffraction analysis.

View full abstract

The viscosities of unary, binary, and ternary eutectic alkali metal carbonate molten salts were measured for the first time by a rotation method using a high-temperature rheometer system and the reliability of the viscosity values was evaluated. The viscosity values obtained in this study are similar to that reported by Sato’s research group, which is considered to have the highest reliability among the studies reported till date. The standard errors in the viscosity values at each temperature are less than ±5%.

View full abstract

In order to synthesize the fine composite oxide powder with uniform composition and good sinterability, reduce the alkaline effluent, and increase the process flexibility by shorten the precipitation time, improvement of the homogeneous precipitation method using the reductant generated by hydrolysis of urea is investigated. Yttria-stabilized zirconia (YSZ) fine powder, which is representative of complex oxide consisting of multiple metal ion, is synthesized by the homogenous precipitation method under high pressure in an autoclave with the microwave irradiation heating. Effects of microwave irradiation heating on microstructure, size, composition uniformity, and sinterability of the powder particles are elucidated. By using the improved method, the hydroxide powder, which is a precursor of the YSZ powder, is generated quickly even when the amount of urea used is not large excess. The YSZ powder particle synthesized by this method is fine and has the uniform composition and good sinterability.

View full abstract

Potassium niobate (KNbO₃) nanocubes were obtained by microwave synthesis. The synthesis was performed using niobium oxide (Nb₂O₅) and potassium hydroxide (KOH) as starting materials. Water was used as the reaction medium. KNbO₃ particles with perovskite structure were confirmed from X-ray diffraction (XRD). The morphology of the KNbO₃ was investigated using transmission electron microscopy (TEM). KNbO₃ nanocubes were synthesized by microwave synthesis at low temperature.

View full abstract

A series of (Gd_2−xLi_x)Ti₂O_7−x with x = 0.050–0.150, abbreviated as GLT-2L were prepared by the addition of 2x mole of LiO_0.5 self-flux in the parent compound. Preparation temperatures were between 1450 and 1500°C depending on the amount of the self-flux addition. Relative densities of all GLT-2L samples were larger than 97.9(3)%. However, the parent compound, Gd₂Ti₂O₇ has no LiO_0.5 co-existence, it has a relative density of 92.8(4)% only, although it was prepared at a higher temperature, 1650°C. Among the GLT-2L samples, the one with x = 0.110 has the highest total electrical conductivity, 6.17(6) × 10⁻⁵ S·cm⁻¹ at 700°C and the lowest activation energy, 0.95(3) eV. Doping Li⁺ ions into the Gd-site of Gd₂Ti₂O₇, preparation temperature was lowered and samples become denser. Meanwhile, vacancies were created and electrical conductivity was increased. At 500°C, average ionic transference numbers (t_i) found for all samples are fully ionic. Increasing temperature, t_i decreases slightly due to the increase of the fractional electronic conductivity of the (Gd_2−xLi_x)Ti₂O_7−x, which is a mixed conductor at high temperature. Ti atoms are in the the mixed valence states.

View full abstract

High-quality (1 − y)(Mg_0.95Mn_0.05)₂(Ti_0.95Sn_0.05)O₄–y(Ca_0.6La_0.8/3)TiO₃ ceramics were prepared by solid-state reaction. The products were characterized by scanning electron microscopy, X-ray diffraction, and network analyzer. (Mg_0.95Mn_0.05)₂(Ti_0.95Sn_0.05)O₄ has a dielectric constant (ε_r) of ~14.21, a high quality factor (Q×f) of ~347,000 GHz, and a temperature coefficient of resonant frequency (τ_f) of ~−57.94 ppm/°C. To produce a temperature-stable material, (Ca_0.6La_0.8/3)TiO₃, which has a large positive τ_f value of +212 ppm/°C, was added to 0.65(Mg_0.95Mn_0.05)₂(Ti_0.95Sn_0.05)O₄–0.35(Ca_0.6La_0.8/3)TiO₃ has an excellent combination of microwave dielectric properties: ε_r ~24.88, Q×f ~133,000, and τ_f = 0 ppm/°C sinter at 1325°C, and can be utilized in the fabrication of microwave devices.

View full abstract

Porous silicon carbide (SiC) ceramics have been a focus of interesting research in the field of porous materials due to their excellent thermal and mechanical properties, which results in wide spread applications in the industrial field. This study presents an approach for the production of porous SiO₂ ceramics using SiC as an additive by the process of direct foaming. The distribution and the microstructure of porous ceramics including the adsorption free energy and Laplace pressure of the particle stabilized colloidal suspension were investigated of around 5.5 × 10⁸ kT and 1.19 mPa respectively to tailor the bubble size and pore size. The wet foam stability was found to be more than 80% and the degree of hydrophobicity achieved from the surfactant (Hexylamine) used can be calculated, measuring the change in the surface tension of the colloidal suspension used.

View full abstract

Tailoring the microstructure of porous materials is essential in order to fulfill the various requirements in industry and daily life. Here we present the macroporous self-setting aluminum trihydroxide (ATH) foams which were fabricated by a direct foaming technique. Sodium dodecyl sulfate (SDS) was used as a surfactant and ATH particles were partially hydrophobized by the adsorption of SDS on its surface. Upon frothing, the foam was stabilized by ATH particles. SDS is a long chain surfactant and has low adsorption energy; therefore the microstructure of the foam was set immediately by the addition of ordinary Portland cement. The self-setting ATH foam obtained by this technique has an average cell size ranging from 69 to 140 µm and porosity in the range of 86 to 93%.

View full abstract

Rare metals could be produced by using a partially stabilized zirconia (PSZ) solid oxide membrane (SOM). The SOM membrane has to expose to a complex fluoride or chloride flux at high temperature. Besides, the SOM membrance was also affected by the loading voltage. In this work, we discussed the corrosion behavior of Calcia-stabilized zirconia (CSZ) in NaF-KF molten salts with different voltage. The results showed that CSZ tubes were eroded in experiments under different temperatures and voltages. This could be attributed to Ca dissolve out from the CSZ matrix, leading metastable tetragonal phase transfer to monoclinic phase. The corrosion rates of exposed to molten and the influence of voltage were also studied, and it was shown that the grain boundaries on the surface were mostly damaged after only 1 h corrosion. However, the CSZ tube could work in molten salts at least 50h. The effect of loading voltage, which could greatly enhance the corrosion behavior, was also studied. The corrosion mechanism of CSZ with different condition was discussed combining microstructures of surface and cross section, EDS and XRD analysis. Based on this work, we could determine the service life of the CSZ tubes and the voltage used in the produced process of rare metals.

View full abstract

MnFe₂O₄ nanocrystals with spinel structure were prepared by conventional solution combustion synthesis and salt-assisted solution combustion synthesis, respectively, and their adsorption capacities for Congo red (CR) were also investigated. The results showed that the MnFe₂O₄ nanocrystals prepared with KCl salt (K-MFO) exhibited much better adsorption capacity for CR than those prepared without KCl (MFO), because the introduction of KCl into the solution combustion synthesis process results in an obvious dispersion and increment of surface area in the obtained MnFe₂O₄ particles. Meanwhile, the MnFe₂O₄ nanocrystals exhibited a clearly ferromagnetic behavior under applied magnetic field, which allowed their high-efficient magnetic separation from wastewater. The adsorption ratio of MnFe₂O₄ nanocrystals prepared with a KCl/M ratio of 2/3 (K-MFO-c) for CR still reached 81% after 5 cycles. By the calculation of Langmuir model, the maximum monolayer adsorption capacity (q_m) of K-MFO-c is 118.76 mg/g and much higher than that of MFO (30.00 mg/g), which must be associated with the higher surface area of K-MFO-c.

View full abstract

The sintering behaviors and microwave dielectric properties of Ba(Co_0.47+xY_0.04Zn_0.35)_1/3Nb_2/3–0.05O₃ (x = 0–0.13) ceramics were investigated in this paper. The XRD results showed all samples exhibited the main phase Ba(Co_1/3Nb_2/3)O₃–Ba(Zn_1/3Nb_2/3)O₃ (BCZN) and a certain amount of secondary phase Ba₅Nb₄O₁₅. SEM revealed that the microstructure was homogeneous fine grained when x equaled to 0.13. The Co deficiency was found unfavorable to improve the microwave dielectric properties of BCZN ceramics and showed remarkable influence on crystal phases and microstructures. The relatively optimized microwave dielectric properties could be obtained when Co was adequate. At last, the Ba(Co_0.6Y_0.04Zn_0.35)_1/3Nb_2/3–0.05O₃ ceramics well-sintered at 1340°C for 20 h had good microwave dielectric properties of ε_r = 35.0, Q×f = 44,833 GHz and τ_f = −1.1 ppm/°C.

View full abstract

The addition of multi-wall carbon nanotubes (MWCNTs) to ceramic matrices can be utilized for special applications such as implant materials. In this study, zirconia toughened alumina (ZTA) composites having 10, 20 and 30 vol % yttria stabilized zirconia (YSZ) with additions of 0.5, 1, and 2 wt % MWCNTs were prepared by spark plasma sintering (SPS) at 1400°C under 40 MPa for 5 min. Systematic investigation of the effects of CNT reinforcement on densification behavior, microstructure, mechanical properties (Vickers microhardness, indentation fracture toughness, and flexural strength) and biocompatibility (cell viability) of ZTA composites was performed. The results indicated that the mechanical properties of CNT reinforced alumina-based composites are strongly dependent on the amount and position of nanotubes in the microstructure and the strength of the cohesion of matrix grains and the nanotubes. Composites with 30 vol % YSZ and 0.5 wt % CNTs exhibited the highest Vickers hardness, fracture toughness and flexure strength with values of ~18 GPa, 5.5 MPa·m^1/2 and 590 MPa, respectively. In addition, preliminary biocompatibility tests indicated that the composites showed no cytotoxicity to human osteoblast cells.

View full abstract

The effect of size and morphology of CeO₂/ZrO₂ catalysts, prepared by impregnation [CZ(IMP)], coprecipitation [CZ(CP)] and deposition–precipitation [CZ(DP)] methods, on the soot oxidation performance was investigated. TEM observation revealed that CeO₂ particles are well dispersed with the size of 10 nm on ZrO₂ support for CZ(IMP). In case of CZ(CP), the agglomeration of CeO₂–ZrO₂ solid solution particles was recognized. On the other hand, large CeO₂ particles (50 nm) were independently present in CZ(DP). Soot oxidation activity of CeO₂/ZrO₂ was strongly dependent on the morphology of CeO₂ particles and decreased in the order of CZ(IMP) > CZ(CP) > CZ(DP). From isotopic transient kinetics analysis using ¹⁸O₂, the lattice oxygen in the surface region of CeO₂ particles in CZ(IMP) was highly reactive compared with those in the surface and bulk of CeZrO_x solid solution in CZ(CP), resulting in high soot oxidation activity.

View full abstract

The dielectric properties of polymorphic tungsten-bronzes, β-SrTa₂O₆ and β′-SrTa₂O₆, were measured using phase pure ceramic specimens. The room temperature dielectric constant (κ) of β-SrTa₂O₆ and β′-SrTa₂O₆ were ≈26 and ≈104, respectively, which were relatively constant over the ac frequency range, 10²–10⁶ Hz. The markedly distinct κ of β- and β′-SrTa₂O₆ were attributed to local structural details, where the displacive Sr disorder in β′-SrTa₂O₆ was emphasized. Both β- and β′-SrTa₂O₆ exhibited a temperature dependent transition of κ with diffuse maxima at 40–80 K.

View full abstract

SiO₂ nanolayer, less than 50 nm in thickness, was coated on hexagonal boron nitride (hBN) plate powders by rotary chemical vapor deposition (RCVD) to assist densification of sinter-hard hBN. In RCVD process, tetraethylorthosilicate (TEOS) precursor heated at 110°C was carried into a reactor by argon, and then reacted with oxygen to form SiO₂ at 700°C, with by-products of CO₂ or H₂O gases vacuumed out the reactor. Full expose of the surface of hBN powders to TEOS, argon and oxygen gases by RCVD technique and stable proceeding of decomposition reaction of TEOS contributed to the uniform distribution of SiO₂ nanolayer. Viscous or liquid flow of uniform SiO₂ nanolayer sintering aids assisted densification process of hBN and elevated its relative density to a maximum value of 96.2% at 1900°C.

View full abstract

Anodic aluminum oxide (AAO) was used as a template coupled with liquid process for synthesis of TiO₂ nanorods and semi-nanotubes. Immersion setting (IS) and vacuum drop setting (VDS) were carried out to insert a TiO₂ precursor solution into AAO pores. With the calcination and NaOH aq. treatment to remove AAO, scanning electron microscopy (SEM) revealed that TiO₂ nanorods with diameter around 100–200 nm were successfully fabricated from IS, whereas TiO₂ semi-nanotubes were given from VDS. The synthesized nanorods or semi-nanotubes were mixed with commercial TiO₂ nanoparticles (P-25) with mixing ratios of 5:95, 10:90 and 15:85 (by mass). The optimum mixing ratios for nanorods and semi-nanotubes are 5:95 and 10:90, respectively. The photoelectrodes made with nanorods or semi-nanotubes showed better performances than the cells used of only P-25, because of the effects of one-dimensional (1-D) nanostructure.

View full abstract

The microstructure formation of Al₂O₃–HfO₂ eutectic prepared by unidirectional solidification and rapid solidification was examined. The microstructure of the Al₂O₃–HfO₂ eutectic samples showed lamellar structure and the relationship between the inter-lamellar spacing λ and solidification rate R can be expressed by λ²R=constant. A small amount of tetragonal HfO₂ phase exists in the sample prepared by rapid solidification. Only monoclinic HfO₂ phase can be found in the eutectic samples prepared by unidirectional solidification. A tensile stress was induced in Al₂O₃ phase during the cooling step due to the transformation of HfO₂ from tetragonal to monoclinic phase. The tensile stress of the Al₂O₃ phase in the eutectic structure was estimated to 420 MPa.

View full abstract

Superhydrophilic alumina films were successfully fabricated by a hydrothermal reaction of nanofibrous alumina films in a nitrilotris(methylenephosphonic acid) (NMP) aqueous solution at 180°C for 6 h. The films showed superhydrophilicity not only as prepared but also after a boiling water resistance test, indicating that they had good durability. The alumina films were phosphorylated wholly in a hydrothermal condition only at 180°C for 6 h. Phosphate moieties were present both at the surface and inside the films and a micro-structure with a serrated morphology was observed over the entire film surface. Whole phosphorylation of the alumina films resulted in good durability in the boiling water resistance test. Other films were phosphorylated partially at 160°C for 6 h and at 180°C for 4 h. The micro-structure with a serrated morphology was observed partially at the film surface. This morphology corresponded to the degree of phosphorylation. These results indicate that the phosphate moieties present on and in the films and the micro-structure of the films produced superhydrophilicity.

View full abstract

Sm³⁺-doped ceria (SDC) nanopowders were prepared via a citrate co-precipitation route. The thermal decomposition of the precursor, SDC structure and morphology were investigated by thermochemical techniques (TGA/DSC), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), surface area analyzer (SAA), scan electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The average crystallite size was observed to be ~7 nm when calcined at 450°C for 4 h. The effect of the ball milling treatment and relative density for the dense sintered-body were also studied. Meanwhile, dense SDC ceramics were successfully prepared by using milled powder under 1250°C and holding for 4 h. The relative density of the obtained SDC ceramics is ~99% with homogeneous microstructure and grain size is ~0.3 µm.

View full abstract

CuFeO₂ crystal thin films were successfully prepared by dip-coating technique through sol–gel route on silica glass substrates. Heat treatment under nitrogen atmosphere was necessary to obtain monovalent Cu and 800–900°C firing was indispensable to prepare CuFeO₂ stable phase, and 2–9 h heat-treatment was appropriate to lower the electrical resistivity. For the dip-coated films, CuO impurity phase was observed in Cu:Fe = 1:1 solution from X-ray diffraction pattern (XRD), and thus the Cu containing solution of Cu:Fe = 0.99:1, 0.97:1, 0.95:1, 0.9:1and 0.8:1 were prepared to eliminate excess CuO phase. Too lower content of Cu such as 0.9:1 and 0.8:1 provided Fe oxides as impurity phase, but slight decrease of Cu iecreased the electric resistivity although CuO was still slightly observed by XRD. The visible transparency of the films was nearly 10%, and some films of conduction type was confirmed as p-type by measuring Hall effect.

View full abstract

The oxynitride phosphor Ca-α-SiAlON:Eu²⁺ has a high thermal tolerance. A series of sodium borosilicate glasses [xNa₂O–(60 − x)B₂O₃–40SiO₂, mol %, x = 2–40] was prepared to investigate their ability to host the Ca-α-SiAlON:Eu²⁺ phosphor powder. The glass-SiAlON phosphor composites, which can emit yellow light when irradiated with blue light (wavelength = 450 nm), were successfully fabricated when the re-melting temperature was 1000 or 1100°C. The chromaticity of the composites, which was estimated from photoluminescence spectra, changed from blue to yellow with increasing SiAlON concentration and sample thickness. This indicates that white light could be generated by controlling the SiAlON concentration and sample thickness. In particular, the 3-mm-thick 10Na₂O–50B₂O₃–40SiO₂ glass with a 2 mass % of phosphor generated near-white light. The quantum efficiency of the composites increased with increasing SiAlON concentration and reached a similar value to that of the phosphor powder, and increased as the Na₂O concentration of the glass decreased.

View full abstract