While lead-free (Li,Na,K)NbO3 piezoceramics have a high Curie temperature (TC > 400 °C) and an excellent piezoelectric constant (d33 > 200 pC/N), the process window regarding the sintering temperature and dwelling time is narrow. Inappropriate sintering conditions can induce the volatilization of A-site alkali ions, leading to a deterioration in dielectric and piezoelectric properties. However, the effect of alkali volatilization on the ferroelastic properties is still uncertain. In this study, (Li,Na,K)NbO3 piezoceramics were deliberately exposed to the sintering temperature for varying times to compare the susceptibility of the effect of alkali volatilization on the ferroelastic properties and compared to changes in the ferroelectric and ferroelastic and dielectric properties.
The dispersion state of barium titanate (BT) particle groups in self-assembled BT/poly-L-lactic-acid (PLLA) composites prepared under different fabrication conditions was investigated. In particular, the BT/PLLA/BT heterointerface in the BT aggregates by the self-assembly process was analyzed and the effect of the BT/PLLA/BT heterointerface and the BT/BT interface on the dielectric properties of BT/PLLA composites were investigated. BT/PLLA composites were fabricated by adding BT particles and BT granules with low and high-speed kneading conditions. The volume fraction of BT in composites varied from 5 to 20 vol.%. The BT aggregates having a BT/PLLA/BT heterointerface were formed under the low-speed kneading condition and the BT agglomerates having a BT/BT interface were formed under the high-speed kneading condition within the self-assembly process. The tan δ of the BT/PLLA composite of self-assembled BT aggregates having the BT/PLLA/BT heterointerface was lower than that of the BT granules having the BT/BT interface. The dielectric constant (ε′) of the self-assembled composite was increased by growing an average secondary particle area of BT fillers. In contrast, the average secondary particle area of BT granules was increased, as compared with 5 vol.% of BT. However, the change in ε′ was saturated. The slopes of the change in the ε′ depending on the secondary particle area of BT fillers were different between the self-assembled BT aggregates having the BT/PLLA/BT heterointerface and the BT granules having the BT/BT interface. Thus, it was suggested that it was an important role in improving the dielectric properties to form ceramic secondary particle groups having the ceramics/polymer/ceramics heterointerface by the self-assembly process.
Ion exchange of Ba to Sr was carried out for spherical BaTiO3 particles (particle size of 600 to 700 nm) by hydrothermal method using strontium nitrate aqueous solution, and the hydrothermal conditions were at 200 °C for 0.5 to 1.5 mol/L for 24 h. After hydrothermal treatment, all samples remained the form and particle size of the source materials. The Sr substituted BaTiO3 sample obtained by hydrothermal treatment with strontium nitrate at 1.5 mol/L showed the composition of Sr0.14Ba0.86TiO3 by elemental analysis by EDX, and the Curie temperature was confirmed to be 90 °C by Raman spectra, respectively.
Conduction of minority carriers in electrolytes is one of the key factors to be controlled to realize highly efficient protonic ceramic fuel cells (PCFCs). In this study, the performance of anode-supported PCFCs using a BaZr0.8Y0.2O3−δ (BZY) monolayer electrolyte membrane and a bilayer electrolyte where a lanthanum tungstate (La28−xW4+xO54+3/2x; LWO) hole-blocking layer is deposited on the BZY membrane are investigated by theoretical calculations based on transport properties of the electrolytes and experimental electrochemical performance tests. The theoretical calculations indicated that the BZY|LWO bilayer cell can achieve higher open-circuit voltage (OCV) and energy efficiency than those of the BZY monolayer cell by suppressing the hole conduction in the electrolyte membrane. We experimentally confirmed that the BZY|LWO cell exhibited the OCV of 1.01 V while that of the BZY monolayer cell was 0.93 V at 600 °C. This study presents that the thin LWO hole-blocking layer is effective in the improvement of the OCV and the energy efficiency of the anode-supported PCFCs.
We synthesized SiO2 glasses doped with various concentrations of Cu (0.001, 0.005, 0.01, and 0.05 mol %) by the spark plasma sintering (SPS) method, and investigated optical, scintillation, and dosimetric properties. The Cu-doped samples indicated photoluminescence (PL) due to the 3d10–3d94s1 transition of Cu+ at around 500 nm under an excitation at 270 nm. The 0.005 % Cu-doped sample showed the highest PL quantum yield (QY) among the present samples, and the QY was 34 %. The decay time constants ascribed to the PL from Cu+ were 47–52 and 121–124 µs. The scintillation and thermally-stimulated luminescence (TSL) peaks were observed to be due to Cu+ as well as PL. The TSL glow curves of all the samples showed two glow peaks around 130 and 300 °C. In TSL dose response functions, the 0.005 and 0.01 % Cu-doped samples showed detection limit of 0.1 mGy.
Nd3xY3−3xAl5O12 (Nd:YAG) powders with high uniformity were synthesized by reverse-titration co-precipitation method. The precipitation formation process and dispersion mechanism of Nd:YAG precursor in co-precipitation process were analyzed, and the influence of the preparation technology on the dispersion of powders was explored by adjusting the concentration of precipitator, alcohol-water solvent and ratio of composite dispersant. In addition, through the analysis of the precursor calcination process, combined with SEM and particle size analysis, it is shown that, under optimum processing conditions, the powders have excellent particle uniformity, narrow particle size distribution and appropriate crystal size when calcined at 1150 °C for 2 h.
The effect of crystal structure of Y-doped ZrO2 as support on the three-way catalytic performance of Rh catalyst was investigated. Rh catalyst supported on 3Y-ZrO2 with tetragonal phase showed higher activity than that on 3Y/ZrO2 with monoclinic phase. The difference in the Rh–support oxide interaction was suspected from the measurements of temperature-programmed reduction by CO (CO-TPR). The use of Y-doped ZrO2 as support was found to contribute to the formation of easily reducible Rh species, resulting in high catalytic activity. Rh species can more strongly interact with 3Y/ZrO2 than with 3Y-ZrO2, resulting in the formation of catalytically active reducible Rh species in Rh/3Y-ZrO2, which showed the highest activity. From Fourier transform infrared (FT-IR) spectroscopy following CO adsorption, no qualitative difference in the surface valence state of Rh particles irrespective of crystallite structure of Y-doped ZrO2 was observed. On the other hand, a large fraction of the surface of Rh particles in Rh/3Y-ZrO2 was found to be Rh0 sites rather than Rh+ sites. This is related to the interaction of Rh particles with Y species in tetragonal 3Y-ZrO2. We concluded that the tetragonal structure of 3Y-ZrO2 with which Rh can interact via Y species is a key-factor to obtain highly active Rh catalysts.
Cobalt metal clusters were synthesized in interlayers of Layered Double Hydroxide (LDH) composed of magnesium and aluminum. Chelate type complex, which is Co-citrate, was used as a precursor of the cluster and intercalated into the interlayer of LDH by ion exchange method. A structural characterization using XRD, IR, TEM-STEM-EELS and nitrogen adsorption/desorption isotherm revealed that Co-citrate was successfully inserted and reduced in the interlayer. Co clusters smaller than 5 nm were formed and catalyzed a hydrolysis reaction of sodium borohydride, resulting in hydrogen generation.
Rare-earth metal bismuth oxynitrates, RBi2O4(NO3) (R: Tb, Dy, Er, Gd, and Ho), were prepared by hydrothermal reactions using hydrated sodium bismuthate (NaBiO3·nH2O) and rare earth nitrates. The optical band gap of the Tb compound was 2.10 eV, and those for the Dy, Er, Gd, and Ho compounds ranged between 2.92 and 2.94 eV. All the compounds were yellowish white in color, except the Tb compound, which was yellowish brown. Surface area of all the compounds varied from 2.46 to 8.17 m2/g. The Tb compound showed the highest photocatalytic activity for phenol degradation under visible light irradiation than other compounds (Dy, Er, Gd, and Ho). At elevated temperatures, TbBi2O4(NO3) was changed to (Tb0.333Bi0.667)O1.50 having a fluorite-type structure, which exhibited poor photocatalytic activity for phenol degradation under visible light irradiation.
A series of boron nitride nanotubes (BNNTs)/ boron carbide (B4C) composite ceramics were prepared using spark plasma sintering (SPS) technology, which uses B4C powders as the matrix and BNNTs as the toughening phase. X-ray diffraction (XRD) and scanning electron microscope (SEM) were then used to characterize the B4C ceramic samples. The effects of the sintering temperature, the BNNTs content, and the matrix particle size on the microstructure and mechanical properties of the B4C composite ceramics were investigated in detail. The experimental results showed that the ceramic samples obtained by adding a 5 wt % BNNTs content sintered at 1750 °C displayed the best mechanical properties. The relative density, microhardness, and fracture toughness were 99.41 %, 32.68 GPa, and 6.87 Mpa·m1/2, respectively. The fracture toughness was 54.59 % higher than that of the composite without the BNNTs. The toughening mechanism of the BNNTs was also studied. The pulling-out of the BNNTs, bridging, and crack branch contributed to the toughness property of the B4C-based ceramic.
In this study, the flexural strength of three kinds of alumina-strengthened porcelains (ASPs), which were recently developed with both small water absorption (WA) and small pyroplastic deformation (PD), was examined using a three-point bending test. The strength of the porcelains was as large as or slightly larger than that of conventional ASPs except for the porcelain made with fine talc powders, in which the accelerated cordierite crystallization suppressed the PD. In addition, the conducted X-ray diffraction, which was analyzed using the Rietveld method, revealed that a lot of alumina particles in the porcelain were consumed for the cordierite crystallization, leading to a decrease in the porcelain strength. This indicates that to realize both small WA and small PD in the material design of porcelains, maintaining the alumina amount as large as possible is important to produce strong porcelains.
Zirconium nitride (ZrN) powders have been prepared by using the zirconium dioxide (ZrO2), sodium azide (NaN3) and metallic magnesium (Mg) as starting materials in a stainless-steel autoclave. The X-ray powder diffraction pattern indicates the formation of cubic phase ZrN. Hafnium nitride (HfN) can also be synthesized from hafnium dioxide (HfO2) through the similar procedure.
The shrinkage rate during a flash event is controlled at a constant value by current ramping for 8 mol %Y2O3–ZrO2 green compact with a rectangular shape. The green compact is heated at a constant heating rate of 5 °C/min until the occurrence of a flash event under a constant alternative current (AC) field of 50 Vrms/cm and 1000 Hz at a limit current of 100 mArms. After the flash event, current ramping is started to keep the shrinkage rate at a constant value of 120 µm/min. Current ramping is conducted by controlling the limit current using a programmable power supply operating in a current control mode. When the limit current reaches 1200 mArms, the sintering condition is kept as it is for 5 min, and the sintering process is completed. 8 mol %Y2O3–ZrO2 sintered polycrystal with a relative density of approximately 99 % and a grain size of about 2.5 µm can be obtained at a furnace temperature of 870 °C for a current ramping and soaking regime of approximately 30 min.