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1.
The effect of variation of sintering temperature (600–800 °C/4 h) on the gas sensing characteristics of a SnO 2:Cu (Cu=9 wt.%) system (a high-performance temperature-selective composition) in the form of pellets is investigated systematically for the CO, H 2 and LPG gases at a concentration level of 1000 ppm. The XRD, SEM and half-bridge techniques were employed to establish the structural, morphological and gas sensing characteristics of the materials, respectively. A very high value of sensitivity factor (SF) equal to 1400 is obtained for CO gas at an optimal operating temperature of 160 °C for the pellets sintered at 750 °C. The selectivity values of CO gas against H 2 and LPG ( SCO/ SH2∼14 and SCO/ SLPG∼280) at an optimum temperature of 160 °C are also improved considerably. This material (SnO 2:Cu, Cu=9 wt.% sintered at 750 °C with an optimal temperature of 160 °C) may prove to have tremendous potential for CO gas sensing applications. 相似文献
2.
Phase-pure bismuth tantalate fluorites were successfully prepared via conventional solid-state method at 900 °C in 24–48 h. The subsolidus solution was proposed with the general formula of Bi 3+x Ta 1?x O 7?x (0 ≤ x ≤ 0.184), wherein the formation mechanism involved a one-to-one replacement of Ta 5+ cation by Bi 3+ cation within ~4.6 mol% difference. These samples crystallised in a cubic symmetry, space group Fm-3 m with lattice constants, a = b = c in the range 5.4477(± 0.0037)–5.4580(± 0.0039) Å. A slight increment in the unit cell was discernible with increasing Bi 2O 3 content, and this may attribute to the incorporation of relatively larger Bi 3+ cation in the host structure. The linear correlation between lattice parameter and composition variable showed that the Vegard’s law was obeyed. Both TGA and DTA analyses showed Bi 3+x Ta 1?x O 7?x samples to be thermally stable as neither phase transition nor weight loss was observed within ~28–1000 °C. The AC impedance study of Bi 3TaO 7 samples was performed over the frequency range 5–13 MHz. At intermediate temperatures, ~350–850 °C, Bi 3+x Ta 1?x O 7?x solid solution was a modest oxide ion conductor with conductivity, ~10 ?6–10 ?3 S cm ?1; the activation energy was in the range 0.98–1.08 eV. 相似文献
3.
In order to synthesize cobalt-based spinel oxides, air was bubbled through aqueous hydroxides suspensions of cobalt and zinc with atomic ratios of Co:Zn = 100:0, 85:15, 67:33 (precisely 2:1), 50:50, 30:70, 15:85, and 0:100 at 70 °C and atmospheric pressure. When cobalt was absent in the suspensions, hexagonal ZnO nanocrystals with ca. 82.2 nm size were observed, whereas cubic Co 3O 4 ones with ca. 52.7 nm were seen when zinc was not present. Zinc-contained cobalt spinel oxides, i.e., Zn x Co 3?x O 4 ( x = 0–1), were obtained when both hydroxides were present, e.g., spherical nanoparticles with ca. 107.6 and 85.0 nm diameters were observed for Co:Zn = 50:50 and 67:33, respectively. The lattice constant, a, for the cubic spinel increased with the increase in zinc atomic %, suggesting the increase in zinc concentration in the spinel. The Zn x Co 3?x O 4 synthesized was normal spinel with a cubic crystal structure, whereas it was also suggested that a very small portion of zinc ion was incorporated into the octahedrally coordinated sites (inversion of spinel). BET surface area of the synthesized catalyst increased with increasing the cobalt atomic % except for Co:Zn = 67:33, for which local minimal surface area was obtained. Oxygen storage capacity of the catalyst was the largest for Co:Zn = 85:15 at 150 and 200 °C, whereas it was for 50:50 at 250 °C. After reducing the synthesized catalysts with hydrogen, metallic cobalt was formed on zinc oxide. CO chemisorption number on the cobalt was the largest for Co:Zn = 67:33, for which the smallest metallic cobalt diameter was also obtained. On the other hand, catalytic CO 2 hydrogenation activity and methane selectivity were the highest for Co:Zn = 50:50, suggesting that zinc oxide as a basic support played an important role in the hydrogenation of acidic CO 2. It was also shown that the catalytic hydrogenation activity and the methane selectivity were higher for the catalysts prepared by the present liquid-phase approach than for those prepared by conventional coprecipitation and impregnation methods, which were ascribed to larger surface area and number of active sites for the former preparation technique than for the latter two. 相似文献
4.
Here, the photocatalytic CO 2 reduction reaction (CO 2RR) with the selectivity of carbon products up to 100% is realized by completely suppressing the H 2 evolution reaction under visible light (λ > 420 nm) irradiation. To target this, plasmonic Au/CdSe dumbbell nanorods enhance light harvesting and produce a plasmon‐enhanced charge‐rich environment; peripheral Cu 2O provides rich active sites for CO 2 reduction and suppresses the hydrogen generation to improve the selectivity of carbon products. The middle CdSe serves as a bridge to transfer the photocharges. Based on synthesizing these Au/CdSe–Cu 2O hierarchical nanostructures (HNSs), efficient photoinduced electron/hole (e ?/h +) separation and 100% of CO selectivity can be realized. Also, the 2e ?/2H + products of CO can be further enhanced and hydrogenated to effectively complete 8e ?/8H + reduction of CO 2 to methane (CH 4), where a sufficient CO concentration and the proton provided by H 2O reduction are indispensable. Under the optimum condition, the Au/CdSe–Cu 2O HNSs display high photocatalytic activity and stability, where the stable gas generation rates are 254 and 123 µmol g ?1 h ?1 for CO and CH 4 over a 60 h period. 相似文献
5.
Two different polymorphs of ferrous oxalate dihydrate were synthesized by precipitation of ferrous ions with oxalic acid: α-Fe(C 2O 4) · 2H 2O with a monoclinic unit cell is obtained after precipitation and ageing at 90 °C, whereas the orthorhombic β-type is formed after precipitation at room temperature. The morphology of the oxalate crystals can be tailored from prismatic crystals of the α-polymorph over star-like aggregates of α/β-mixtures to non-agglomerated crystallites of β-oxalate. Thermal decomposition in air gives hematite at T ≥ 250 °C; if the thermolysis reaction is performed at low oxygen partial pressures (e.g., T = 500 °C and p O2 = 10 ?25 atm) magnetite is obtained. The synthesized magnetite is stoichiometric as signaled by lattice parameters of a 0 = 8.39 Å. The thermal decomposition of ferrous oxalate is monitored by thermal analysis, XRD, and IR-spectroscopy. The morphology of the oxalate crystals is preserved during thermal decomposition; the oxalates are transformed into spinel particle aggregates of similar size and shape. The crystallite size of the magnetite particles increases with temperature and is 40 or 55 nm, if synthesized from β-oxalate at 500 °C or 700 °C, respectively. The saturation magnetization of the magnetite particles decreases with decreasing particle size. Since the particles are larger than the critical diameter for superparamagnetic behavior they display hysteresis behavior at room temperature. 相似文献
6.
Copper aluminum oxide (CuAlO 2) with delafossite phase was synthesized by the Pechini method using different calcination temperatures to evaluate its influence on the structure and thermoelectric material properties. X-ray diffraction and Raman spectroscopy confirm that delafossite phase was formed at 1100 °C with the presence of 2 H-CuAlO 2 and Al 2O 3 impurities, while at lower calcination temperatures (900 and 1000 °C), a mixture of CuO + CuAl 2O 4 (spinel phase) was observed. Energy-dispersive X-ray elemental maps display an even distribution of copper, aluminum and oxygen in the sample calcined at 1100 °C. Direct optical band gap, E g = 3.6 eV, was calculated from reflectance diffuse spectra by Kubelka–Munk and Tauc methods. An absorption band at 1.7 eV accounts for defect levels, masking the characteristic indirect transition. The thermoelectric properties, such as Seebeck coefficient, and thermal and electrical conductivities of the sample calcined at 1100 °C were measured at different temperatures. Hall voltage and positive values of the Seebeck coefficient (425.8–434.4 µV K ?1) confirm the material’s p-type character. The independence of the Seebeck coefficient on the operation temperature indicates a small polaron electrical conduction mechanism. Thermal conductivity decreases exponentially with the temperature from 43.45 to 23.9 W m ?1 K ?1, where the principal contribution is due to phonons. Figure of merit ZT of sample calcined at 1100 °C between 100 and 800 °C increases from 1.42 × 10 ?8 to 4.94 × 10 ?4 in the order of the literature reports. From the Arrhenius plot ln( σT) versus 1000/ T, an activation energy E a = 0.32 eV for the electrical conductivity was calculated. 相似文献
7.
The purpose of this study is to understand the effects of substrate temperature (ST) and post deposition annealing (PDA) on the structural-electrical properties of Gd 2O 3 film and to evaluate the electrical performances of the MOS based devices formed with this dielectric. The Gd 2O 3/Si structures were annealed at 500, 600, 700, and 800 °C under N 2 ambient after the films were grown on heated p-Si substrate at various temperatures ranged from 20 to 300 °C by RF magnetron sputtering. For any given ST, the crystallization/grain size increased with increasing PDA temperature. The bump in the accumulation region or continuous decrease in the capacitance values of the inversion region of the C–V curves for 800 °C PDA was not observed. The lowest effective oxide charge density ( Q eff ) value was obtained to be ??1.13?×?10 11 cm ?2 from the MOS capacitor with Gd 2O 3, which is grown on heated Si at 300 °C and annealed at 800 °C. The density of the interface states ( D it ) was found to be in the range of 0.84?×?10 11 to 1.50?×?10 11 eV ?1 cm ?2. The highest dielectric constant ( ε) and barrier height \(({\Phi _B})\) values were found to be 14.46 and 3.68, which are obtained for 20 °C ST and 800 °C PDA. The results show that the negative charge trapping in the oxide layer is generally more than that of the positive, but, it is reverse of this situation at the interface. The leakage current density decreased after 20 °C ST, but no significant change was observed for other ST values. 相似文献
8.
Microalgae cultivation and biomass to biochar conversion is a potential approach for global carbon sequestration in microalgal biorefinery. Excessive atmospheric carbon dioxide (CO 2) is utilized in microalgal biomass cultivation for biochar production. In the current study, microalgal biomass productivity was determined using different CO 2 concentrations for biochar production, and the physicochemical properties of microalgal biochar were characterized to determine its potential applications for carbon sequestration and biorefinery. The indigenous microalga Chlorella vulgaris FSP-E was cultivated in photobioreactors under controlled environment with different CO 2 gas concentrations as the sole carbon source. Microalgal biomass pyrolysis was performed thereafter in a fixed-bed reactor to produce biochar and other coproducts. C. vulgaris FSP-E showed a maximum biomass productivity of 0.87 g L ?1 day ?1. A biochar yield of 26.9% was obtained from pyrolysis under an optimum temperature of 500 °C at a heating rate of 10 °C min ?1. C. vulgaris FSP-E biochar showed an alkaline pH value of 8.1 with H/C and O/C atomic ratios beneficial for carbon sequestration and soil application. The potential use of microalgal biochar as an alternative coal was also demonstrated by the increased heating value of 23.42 MJ kg ?1. C. vulgaris FSP-E biochar exhibited a surface morphology, thereby suggesting its applicability as a bio-adsorbent. The cultivation of microalgae C. vulgaris FSP-E and the production of its respective biochar is a potential approach as clean technology for carbon sequestration and microalgal biorefinery toward a sustainable environment. 相似文献
9.
In order to compare the electrochemical performance of Ce 0.9Gd 0.1O 2−δ (CGO) in various fuels, impedance spectroscopy measurements were carried out in the atmospheres containing H 2, CO, CO 2, CH 4, N 2 at various compositions, in the temperature range 650°C to 850°C. Ohmic loss and polarization resistance were derived from impedance spectroscopy measurements. The stability at different temperatures of the anode was also investigated in 9%H 2/91%N 2 humidified with 3% H 2O. The microstructure of the anode before and after degradation test was analysed by SEM. These investigations indicated similarities in the impedance and the activation enthalpies in hydrogen/water, methane/water and CO/CO 2 atmospheres. No indications of methane cracking leading to carbon formation were found. 相似文献
10.
Camphor, C 10H 16O, as a natural and renewable carbon precursor, can be pyrolyzed to pyrolytic carbon (PyC; pyrocarbon) with significant industrial applications from conducting electrodes to biomedical implant coatings. Here, a simple but controllable chemical vapor deposition setup, operating at low temperatures (650–800 °C) in nitrogen atmosphere at ambient pressure in the absence of catalyst, was used. According to XRD and Raman spectroscopy, nanocrystalline thin PyC films were obtained at this temperature range without a significant change in L c and d 002 values. When the deposition temperature increased from 700 to 800 °C, L a and crystallinity percentage values were increased from 2.40 nm and 73.16% to 4.15 nm to 87.58%, respectively. SEM and AFM analyses showed smooth ( Ra ≈ 1 nm) and shiny surface for the thin films with 10–500-nm range thickness. The films were hydrophilic on surface (water contact angle ≈ 72.45°) with surface free energy of ≈ 41 mN/m. Young’s modulus, hardness and friction coefficient of the thin PyC coatings were calculated using nanoindentation technique as ≈ 29.9, 3.5 GPa and 0.09, respectively. Resistivity of the films was 2.21 × 10 ?5 Ωm, so it can be anticipated to repel the blood cells. Cytocompatibility screening in direct contact mode and in vitro biocompatibility findings supported cyto- and hemocompatible properties for the PyC specimens synthesized from camphor. 相似文献
11.
The CO 2 reduction reaction (CO 2RR) driven by renewable electricity represents a promising strategy toward alleviating the energy shortage and environmental crisis facing humankind. Cu species, as one type of versatile electrocatalyst for the CO 2RR, attract tremendous research interest. However, for C 2 products, ethanol formation is commonly less favored over Cu electrocatalysts. Herein, AuCu alloy nanoparticle embedded Cu submicrocone arrays (AuCu/Cu‐SCA) are constructed as an active, selective, and robust electrocatalyst for the CO 2RR. Enhanced selectivity for EtOH is gained, whose Faradaic efficiency (FE) reaches 29 ± 4%, while ethylene formation is relatively inhibited (16 ± 4%) in KHCO 3 aqueous solution. The ratio between partial current densities of EtOH and C 2H 4 ( jEtOH/ jC2H4) can be tuned in the range from 0.15 ± 0.27 to 1.81 ± 0.55 by varying the Au content of the electrocatalysts. The combined experimental and theoretical calculation results identify the importance of Au in modifying binding energies of key intermediates, such as CH 2CHO*, CH 3CHO*, and CH 3CH 2O*, which consequently modify the activity and selectivity ( jEtOH/ jC2H4) for the CO 2RR. Moreover, AuCu/Cu‐SCA also shows high durability with both the current density and FE EtOH being largely maintained for 24 h electrocatalysis. 相似文献
12.
This study reports the effect of coronene (C 24H 12) addition on some superconducting properties such as critical temperature ( Tc), critical current density ( Jc), flux pinning force density ( Fp), irreversibility field ( Hirr), upper critical magnetic field ( Hc2), and activation energy ( U0), of bulk MgB 2 superconductor by means of magnetisation and magnetoresistivity measurements. Disk-shaped polycrystalline MgB 2 samples with varying C 24H 12 contents of 0, 2, 4, 6, 8, 10 wt%, were produced at 850 °C in Ar atmosphere. The obtained results show an increase in field- Jc values at 10 and 20 K resulting from the strengthened flux pinning, and a decrease in critical temperature ( Tc) because of C substitution into MgB 2 lattice, with increasing amount of C 24H 12 powder. The Hc2(0) and Hirr(0) values are respectively found as 144, 181, 172 kOe, and 128, 161, 145 kOe for pure, 4 wt% and 10 wt% C 24H 12 added samples. The U0 depending on the magnetic field curves were plotted using thermally activated flux flow model. The maximum U0 values are respectively obtained as 0.20, 0.23 and 0.12 eV at 30 kOe for pure, 4 wt% and 10 wt% C 24H 12 added samples. As a result, the superconducting properties of bulk MgB 2 at high fields was improved using C 24H 12, active carbon source addition, because of the presence of uniformly dispersed C particles with nanometer order of magnitude, and acting as effective pinning centres in MgB 2 structure. 相似文献
13.
In this study, Na-substituted Bi 2Sr 2Ca 0.9Na 0.1 Cu 2O superconductor samples were prepared by a polymer solution method. Three different sintering temperatures (850, 860, and 870 °C) were used to study the effect of Na substitution. The samples have been characterized using X-ray diffraction, scanning electron microscopy (SEM), DC electrical resistivity, and DC magnetic measurements. Magnetoresistivity measurements have shown a broadening of the superconducting transition under magnetic field which is explained on the basis of the thermally activated flux flow (TAFF) model. The calculated flux pinning energies of the samples varied from 0.17 to 0.02 eV by means of increasing magnetic field 0 to 9 T. The upper critical magnetic field H c2(0) and the coherence length ( ζ(0)) at T = 0 K were calculated using the resistivity data. H c2(0) and ξ(0) values have been calculated as 194, 144, and 139 T and 15.5, 15.2, and 13 Å at 850, 860, and 870 °C, respectively. TAFF model has shown Bi 2Sr 2Ca 0.9Na 0.1Cu 2O 8+y flux pinning energies are 0.015 eV at 9 T in all cases, while they were 0.165, 0153, and 0.149 eV at 0 T for samples sintered at 850, 860, and 870 °C, respectively. 相似文献
14.
CeO 2 and Co 3O 4–CeO 2 nanoparticles were synthesized, thoroughly characterized, and evaluated in the COPrOx reaction. The CeO 2 nanoparticles were synthesized by the diffusion-controlled precipitation method with ethylene glycol. A notably higher yield was obtained when H 2O 2 was used in the synthesis procedure. For comparison, two commercial samples of CeO 2 nanoparticles (Nyacol ®)—one calcined and the other sintered—were also studied. Catalytic results of bare CeO 2 calcined at 500 °C showed a strong influence of the method of synthesis. Despite having similar BET area values, the CeO 2 synthesized without H 2O 2 was the most active sample. Co 3O 4–CeO 2 catalysts with three different Co/(Co + Ce) atomic ratios, 0.1, 0.3, and 0.5, were prepared by the wet impregnation of the CeO 2 nanoparticles. TEM and STEM observations showed that impregnation produced mixed oxides composed of small CeO 2 nanoparticles located both over the surface and inside the Co 3O 4 crystals. The mixed oxide catalysts prepared with a cobalt atomic ratio of 0.5 showed methane formation, which started at 200 °C due to the reaction between CO 2 and H 2. However, above 250 °C, the reaction between CO and H 2 became important, thus contributing to CO elimination with a small H 2 loss. As a result, CO could be totally eliminated in a wide temperature range, from 200 to 400 °C. The methanation reaction was favored by the reduction of the cobalt oxide, as suggested by the TPR experiments. This result is probably originated in Ce–Co interactions, related to the method of synthesis and the surface area of the mixed oxides obtained. 相似文献
15.
Trace gases such as H 2O, CO, CO 2, NO, N 2O, NO 2 and CH 4 strongly absorb in the mid-IR (>2.5 μm) spectral region due to their fundamental rotational and vibrational transitions. CH 4 gas is relatively non-toxic, however, it is extremely explosive when mixed with other chemicals in levels as low as 5% and it can cause death by asphyxiation. In this work, we propose a silicon strip waveguide at 3.39 μm for CH 4 gas sensing based on the evanescent field absorption. These waveguides can provide the highest evanescent field ratio (EFR)>55% with adequate dimensions. Moreover, EFR and sensitivity of the sensor are highly dependent on the length of the waveguide up to a certain limit. Therefore, it is always a compromise between the length of the waveguide and EFR in order to obtain greater sensitivity. 相似文献
16.
Biogas has limited use in energy generation mainly due to the presence of hydrogen sulfide (H 2S). Currently, most of the techniques employed in the removal of H 2S from biogas have a chemical base, with high material costs and generating secondary pollutants. Biological processes for H 2S removal have become effective and economical alternative techniques to traditional gas-treatment systems based on physicochemical techniques. Therefore, the aim of this work was to investigate the performance of a bench-scale biofilter for the removal of H 2S present in synthetic biogas. In addition, CO 2 and CH 4 concentrations in the outlet biogas were evaluated. The inoculum used in the experiment was composed of Acidithiobacillus thiooxidans fixed on a packing of wood chips. Synthetic biogas was supplied to the system with a composition of 60 % CH 4, 39 % CO 2 and 1 % H 2S. The biofilter operated continuously for 37 days with an average H 2S removal efficiency of 75 ± 13 % and maximum of 97 %. The elimination capacity of the system reached an average of 130 ± 23 g m ?3 h ?1 and a maximum of 169 g m 3 h ?1. The biofiltration system showed an average reduction of only 6 % in CH 4 concentration from biogas. Thus, besides being efficient in the removal of H 2S, the system was able to maintain the biogas energy value. 相似文献
17.
The effect of defect ion concentration on conductivity in the CaNd 2S 4 system has been investigated by varying the CaS:Nd 2S 3 ratio. Samples with the formula xCaS:Nd 2S 3 x = 0.7–1.0 have been prepared using solid state methods by high temperature synthesis in evacuated quartz tubes followed by annealing in hydrogen sulfide. The structures of the materials were determined using the Rietveld refinement of powder neutron diffraction data. The phases crystallise with a defect version of the cubic Th 3P 4 structure in the space group I-43d with cell parameter a ≈ 8.53 Å. Temperature programmed oxidation (TPO) in a 5 Vol.% O 2/Ar atmosphere show that the materials resist oxidation up to a temperature of approximately 680 °C. TPO also indicates that there is only one type of sulfide ion present in the system, based on the presence of only one peak in the TPO trace. In-situ impedance spectroscopy was carried out in an Ar and H 2S/Ar atmosphere between 300 °C and 500 °C. Bulk conductivities, activation energies and time constants for ion hopping processes were determined. The sample, 0.9CaS:Nd 2S 3, was found to exhibit three impedance arcs in the Nyquist plot suggesting ionic conduction. The independence of the material’s bulk conductivity when exposed to an H 2S/Ar atmosphere supports this statement. The xCaS:Nd 2S 3 sample with x ≤ 0.8 show strong electronic contributions to the overall conductivity. The total ionic conductivity for 0.9CaS:Nd 2S 3 of 1.09 × 10 ?6 S cm ?1 measured at 500 °C, matches conductivity values reported using galvanic cells. 相似文献
18.
In this study, the catalytic activities of the steam methane reforming (SMR) reactions with two catalysts, including nickel–scandia-stabilized zirconia (Ni–SSZ) and copper/nickel–scandia-stabilized zirconia (Cu/Ni–SSZ), were examined and compared. The microstructure and crystallinity of the as-prepared catalysts were characterized by scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. Mass spectrometer was applied in the outlet streams, in order to simultaneously monitor the time-dependent kinetics in the reactor for an activity test and conversion examination. Finally, thermogravimetric analysis (TGA) and Raman spectrometer were implemented for further verification of carbon residuals on the catalysts. It was found that the incorporation of Cu on Ni–SSZ imposed significant constraints on the growth of nickel crystallites from NiO during the annealing process in reducing atmospheres. The methane conversion of Ni–SSZ and Cu/Ni–SSZ catalysts (annealed at 300 °C for 2 h) was 36.2 and 26.0%, respectively. However, the amount of carbon residuals on Cu/Ni–SSZ catalyst (300 °C for 2 h) was 18.6%, which is lower than that of the Ni–SSZ catalysts (33.2%) from TGA results. Further Raman experiments revealed that more graphite-like carbon residuals and less defects or amorphous carbons ( IG/ ID?=?2.0) were found in the case of Cu/Ni–SSZ catalysts (300 °C for 2 h). Among the catalysts in this study, the Cu/Ni–SSZ catalyst (300 °C for 2 h) is considered as a promising catalyst for SMR reaction, since it has a fair methane conversion, and characterized higher CO 2 selectivity and lower CO selectivity without compromising the hydrogen purity. More importantly, the least amount of carbon residuals was found in Cu/Ni–SSZ catalyst (300 °C for 2 h), which assured a better lifetime. 相似文献
19.
In this study, the powders of the Ba0.75Sr0.25TiO3 (BST) nanoparticles were directly synthesized by milling of Ba(OH)2·8H2O, Sr(OH)2·8H2O, and Ti(BuO)4 in ethanol at room temperature. They have homogenous grains of?~?15 nm and high sintering activity. The dense ceramics with the density?>?90% can be obtained at a sintering temperature of?≤?950 °C by adding 3 wt% sintering aids of Bi2O3 and Li2CO3. Several Bi-related intermediate compounds act as perovskite-structured templates to sintering the ceramics at a different temperature. They enhance the mass transfer and promote the sintering densification. These compounds such as Ba2BiO4 and SrBiO4 appear at 800 °C, LiBa4Bi3O11 and Sr1.2Bi0.8O3 appear over 830 °C, and Bi8.11Ba0.89O13.05 appears at 950 °C. The cation Bi in them can have mixture valences of 3+ and 5+. It makes the ceramics as semiconducting state with the dark gray color and decreases the ceramic resistivities. With the sintering temperature increase, especially at 950 °C, the cation Bi tends back to single valence of +3 in the ceramics. The most of alkaline earth cations in Bi-related compounds will release and resorb into the lattice of BST and drive the sintering densification. The BST ceramics can have a peak dielectric constant?>?6500 (at 53 °C) with loss?<?0.025 at 10 kHz, and resistivity?>?1012 Ω cm when sintered at a temperature of?≥?900 °C with 3 wt% sintering aids. They have a potential application for multiple layer ceramic capacitors (MLCC) with silver inner electrodes. 相似文献
20.
Novel LiBaPO 4:Bi 3+ yellow-emitting phosphor is synthesized by high temperature solid-state reaction method in air. With excitation 260 nm, LiBaPO 4:Bi 3+ phosphor emits yellow light with the chromaticity coordinate (0.4272, 0.4657) and color rendering index 77.7. Emission band peaking at ~?588 nm of LiBaPO 4:Bi 3+ phosphor in the range of 400–790 nm is attributed to the 3P1 → 1S0 electron transition of Bi 3+ ion. Excitation band monitored at 588 nm in the range of 220–300 nm is assigned to the 1S0 → 3P1 electron transition of Bi 3+ ion. The optimal Bi 3+ ion concentration in LiBaPO 4:Bi 3+ phosphor is ~?1.0 mol%. Time resolved spectra and fluorescence lifetime data confirm that there is only Bi 3+ ion luminous center in LiBaPO 4:Bi 3+ phosphor. The luminous mechanism is analyzed by configurational coordinate diagram of Bi 3+ ion. The experiment results are helpful to develop other new Bi 3+-doped optical materials for solid-state lighting. 相似文献
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