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1.
Sol–gel derived Bi2Ti2O7 ceramic powders have been prepared from methoxyethoxides of bismuth and titanium (molar ratio of Ti/Bi = 1.23 and water/alkoxides = 1.31). The Bi2Ti2O7 phase was stable at a low temperature (700 °C), but it then transformed into mixed phases of Bi4Ti3O12 and Bi2Ti4O11 at 850–1150 °C. The single phase of Bi2Ti2O7 reoccurred at 1200 °C. Dielectric properties and ferroelectric behavior of samples sintered at 1150 and 1200 °C were examined. Under frequency of 1 MHz, samples sintered at 1150 and 1200 °C had a dielectric constant of 101.3 and 104.2, and a loss tangent of 0.0193 and 0.0145, respectively. Only the sample sintered at 1150 °C showed ferroelectric behavior, where remanent polarization is 3.77 μC cm−2 and coercive field is 24 kV cm−1. Thus, the Bi2Ti2O7 did not exhibit ferroelectricity, but the mixed phase of Bi4Ti3O12 and Bi2Ti4O11 did.  相似文献   

2.
The microstructure, electrical properties, dielectric characteristics, and DC-accelerated aging behavior of the ZnO–V2O5–MnO2 system sintered were investigated for MnO2 content of 0.0–2.0 mol% by sintering at 900 °C. For all samples, the microstructure of the ZnO–V2O5–MnO2 system consisted of mainly ZnO grain and secondary phase Zn3(VO4)2. The incorporation of MnO2 to the ZnO–V2O5 system was found to restrict the abnormal grain growth of ZnO. The nonlinear properties and stability against DC-accelerated aging stress improved with the increase of MnO2 content. The ZnO–V2O5–MnO2 system added with MnO2 content of 2.0 mol% exhibited not only a high nonlinearity, in which the nonlinear coefficient is 27.2 and the leakage current density is 0.17 mA/cm2, but also a good stability, in which %ΔE1 mA = −0.6%, %Δ = −26.1%, and %Δtan δ = +22% for DC-accelerated aging stress of 0.85E1 mA/85 °C/24 h.  相似文献   

3.
Thin films of the system xAl2O3–(100 − x)Ta2O5–1Er2O3 were prepared by a sol–gel method and a dip-coating technique. The influences of the composition and the crystallization of the films on Er3+ optical properties were investigated. Results of X-ray diffraction indicated that the crystallization temperature of Ta2O5 increased from 800 to 1000 °C with increased values of x. In crystallized films, the intensities of the visible fluorescence and upconversion fluorescence tend to decrease with an increase in x values, due to the high phonon energy of Al2O3; the strongest fluorescence is observed in a crystallized film for x = 4 heat treated at 1000 °C. In amorphous films obtained by heat treatment at relatively low temperatures the Er3+ fluorescence could not be observed because strong fluorescence from organic residues remaining in the films thoroughly covered the Er3+ fluorescence. On the other hand, the Er3+ upconversion fluorescence in the amorphous films was observed to be stronger than that in the crystallized films. The strongest upconversion fluorescence is observed in an amorphous film for x = 75 heat treated at 800 °C.  相似文献   

4.
The BaxSr1−xTiO3 (BST)/Pb1−xLaxTiO3 (PLT) composite thick films (20 μm) with 12 mol% amount of xPbO–(1 − x)B2O3 glass additives (x = 0.2, 0.35, 0.5, 0.65 and 0.8) have been prepared by screen-printing the paste onto the alumina substrates with silver bottom electrode. X-ray diffraction (XRD), scanning electron microscope (SEM) and an impedance analyzer and an electrometer were used to analyze the phase structures, morphologies and dielectric and pyroelectric properties of the composite thick films, respectively. The wetting and infiltration of the liquid phase on the particles results in the densification of the composite thick films sintered at 750 °C. Nice porous structure formed in the composite thick films with xPbO–(1 − x)B2O3 glass as the PbO content (x) is 0.5 ≥ x ≥ 0.35, while dense structure formed in these thick films as the PbO content (x) is 0.8 ≥ x ≥ 0.65. The volatilization of the PbO in PLT and the interdiffusion between the PLT and the glass lead to the reduction of the c-axis of the PLT phase. The operating temperature range of our composite thick films is 0–200 °C. At room temperature (20 °C), the BST/PLT composite thick films with 0.35PbO–0.65B2O3 glass additives provided low heat capacity and good pyroelectric figure-of-merit because of their porous structure. The pyroelectric coefficient and figure-of-merit FD are 364 μC/(m2 K) and 14.3 μPa−1/2, respectively. These good pyroelectric properties as well as being able to produce low-cost devices make this kind of thick films a promising candidate for high-performance pyroelectric applications.  相似文献   

5.
Synthesis and single crystal structure are reported for a new gadolinium acid diphosphate tetrahydrate HGdP2O7·4H2O. This salt crystallizes in the monoclinic system, space group P21/n, with the following unit-cell parameters: a = 6.6137(2) Å, b = 11.4954(4) Å, c = 11.377(4) Å, β = 87.53(2)° and Z = 4. Its crystal structure was refined to R = 0.0333 using 1783 reflections. The corresponding atomic arrangement can be described as an alternation of corrugated layers of monohydrogendiphosphate groups and GdO8 polyhedra parallel to the () plane. The cohesion between the different diphosphoric groups is provided by strong hydrogen bonding involving the W4 water molecule.

IR and Raman spectra of HGdP2O7·4H2O confirm the existence of the characteristic bands of diphosphate group in 980–700 cm−1 area. The IR spectrum reveals also the characteristic bands of water molecules vibration (3600–3230 cm−1) and acidic hydrogen ones (2340 cm−1). TG and DTA investigations show that the dehydration of this salt occurs between 79 and 900 °C. It decomposes after dehydration into an amorphous phase. Gadolinium diphosphate Gd4(P2O7)3 was obtained by heating HGdP2O7·4H2O in a static air furnace at 850 °C for 48 h.  相似文献   


6.
Bi2O3·B2O3 glasses doped with rare-earth oxides (RE2O3) (RE3+ = La3+, Pr3+, Sm3+, Gd3+, Er3+ and Yb3+) were prepared by the melting–quenching method. The relationships between composition and properties were demonstrated by IR, DSC, XRD and SEM analysis. The results show that the network structure resembles that of undoped Bi2O3·B2O3 glass, composing of [BO3], [BO4] and [BiO6] units. RE2O3 stabilizes the glass structure as a modifier. Transition temperature (Tg) increases linearly with cationic field strength (CFS) of RE3+. La2O3, Pr2O3, Sm2O3 and Gd2O3 are benefit to promote the formation of BiBO3 crystal. When Er2O3 and Yb2O3 are introduced, respectively, the main crystal phase changes to Bi6B10O24. Transparent surface crystallized samples are obtained by reheating at 460–540 °C for 5 h. In this case, needle like BiBO3 crystal or rare-earth-doped BiBO3 crystal (PrxBi1−xBO3 and GdxBi1−xBO3) are observed, which is promising for non-linear optical application.  相似文献   

7.
《Materials & Design》1997,18(4-6):395-399
This study shows that homogeneous composite compacts with improved superconducting and mechanical properties can be successfully prepared from pure Me–HTSC powders (Me=Ag, Cu, Al; HTSC=YBA2Cu3O7−x). Composites were produced under the following conditions: the mass fraction of the metal phase was in the range 2.5–40 wt%, the compacting pressure was 30 kN/cm2, the sintering temperature was from 270 to 950°C and the cooling rate was 50°C/h and 220°C/min. Microstructure and X-ray diffraction analysis have been done, alongside the Tc value determination.  相似文献   

8.
We report on the properties of (1−x)SrBi2Ta2O9xBi3TaTiO9 solid solution thin films for ferroelectric non-volatile memory applications. The solid solution thin films fabricated by modified metalorganic solution deposition technique showed much improved properties compared to SrBi2Ta2O9. A pyrochlore free crystalline phase was obtained at a low annealing temperature of 600°C and grain size was found to be considerably increased for the solid solution compositions. The film properties were found to be strongly dependent on the composition and annealing temperatures. The measured dielectric constant of the solid solution thin films was in the range 180–225 for films with 10–50% of Bi3TaTiO9 content in the solid solution. Ferroelectric properties of (1−x)SrBi2Ta2O9xBi3TaTiO9 thin films were significantly improved compared to SrBi2Ta2O9. For example, the observed remanent polarization (2Pr) and coercive field (Ec) values for films with 0.7SrBi2Ta2O9–0.3Bi3TaTiO9 composition, annealed at 650°C, were 12.4 μC/cm2 and 80 kV/cm, respectively. The solid solution thin films showed less than 5% decay of the polarization charge after 1010 switching cycles and good memory retention characteristics after about 106 s of memory retention. The improved microstructural and ferroelectric properties of (1−x)SrBi2Ta2O9xBi3TaTiO9 thin films compared to SrBi2Ta2O9, especially at lower annealing temperatures, suggest their suitability for high density FRAM applications.  相似文献   

9.
Dense TiC–Al2O3–Al composite was prepared with Al, C and TiO2 powders by means of electric field-activated combustion synthesis and infiltration of the molten metal (here Al) into the synthesized TiC–Al2O3 ceramic. An external electric field can effectively improve the adiabatic combustion temperature of the reactive system and overcome the thermodynamic limitation of reaction with x < 10 mol. Thereby, it can induce a self-sustaining combustion synthesis process. During the formation of Al2O3–TiC–Al composite, Al is molten first, and reacted with TiO2 to form Al2O3, followed by the formation of TiC through the reaction between the displaced Ti and C. Highly dense TiC–Al2O3–Al with relative density of up to 92.5% was directly fabricated with the application of a 14 mol excess Al content and a 25 V cm−1 field strength, in which TiC and Al2O3 particles possess fine-structured sizes of 0.2–1.0 μm, with uniform distribution in metal Al. The hardness, bending strength and fracture toughness of the synthesized TiC–Al2O3–Al composite are 56.5 GPa, 531 MPa and 10.96 MPa m1/2, respectively.  相似文献   

10.
The microstructure and piezoelectric properties of the 0.01Pb(Mg1/2W1/2)O3–0.41Pb(Ni1/3Nb2/3)O3–0.35PbTiO3–0.23PbZrO3 + 0.1 and 0.3 wt.% Y2O3 + x ZnO ceramics were investigated. The crystal structure changed from psudocubic to tetragonal when ZnO added. The average grain size increased from 4 μm to 8 μm with the addition of ZnO by oxygen diffusion, even if the growth rate was low. When ZnO added until 0.5 wt.%, the , kp and d33 values of specimens were slightly increased regardless Y2O3 contents. The curie point of PMW–PNN–PT–PZ ceramics were increased from 162 °C to 232 °C, as increasing the ZnO contents. When ZnO added, the kp of specimens slightly was increased regardless Y2O3 contents. The mechanical quality factors were abruptly decreased regardless Y2O3 contents, when ZnO added until 0.75 wt.%. The optimized piezoelectric properties were obtained; d33 = 730 (pC/N), kp = 60, Qm = 50, and  = 4750, when PMW–PNN–PT–PZ + 0.3 wt.% Y2O3 + 0.5 wt.% ZnO sintered at 1200 °C for 1 h.  相似文献   

11.
This paper presents the observations of the study on arsenic removal from a contaminated ground water (simulated) by adsorption onto Fe3+ impregnated granular activated carbon (GAC-Fe). Fe2+, Fe3+ and Mn2+ have also been considered along with arsenic species in the water sample. Similar study has also been done with untreated granular activated carbon (GAC) for comparison. The effects of adsorbent dose, particle size of adsorbent and initial arsenic concentration on the removal of As(T), As(III), As(V), Fe2+, Fe3+ and Mn2+ have been discussed. Under the experimental conditions, the optimum adsorbent doses for GAC-Fe and GAC have been found to be 8 g/l and 24 g/l, respectively with an agitation time of 15 h. Particle size of the adsorbents (both GAC and GAC-Fe) has shown negligible effect on the removal of arsenic and Fe species. However, for Mn removal the effect of adsorbent particle size is comparatively more. Percentage removal of As(T), As(V) and As(III) increase with the decrease in initial arsenic concentration (As0). However, the increase in percentage removal of all the arsenic species with decrease in As0 are less for higher value of As0 (3000–500 ppb) than those of the lower value of As0 (500–10 ppb). The % removal of As(T), As(III), As(V), Fe, and Mn were 95%, 92.4%, 97.6%, 99% and 41.2%, respectively when 8 g/l GAC-Fe was used at the As0 value of 200 ppb. However, for GAC these values were 55.5%, 44%, 71%, 98% and 97%. The pH and temperature of the study were 7 ± 0.1 and 30 ± 1 °C, respectively.  相似文献   

12.
The inhibition performance of PWVA/Sb2O3 complex inhibitor on carbon steel was studied in 55%LiBr + 0.07 mol L−1 LiOH solution. Results indicated that the complex inhibitor decreased both anodic and cathodic polarization current density and widened the passive potential region of carbon steel in test solution and can be classified as mixed inhibitor. The complex inhibitor exhibited excellent inhibition performance on carbon steel when the concentrations of PWVA and Sb2O3 were 300 and 200 mg L−1, respectively. With the solution temperature increasing from 145 to 240 °C, the corrosion rates of carbon steel increased from 4.71 to 120.66 μm y−1. In solution containing the complex inhibitor, the relationship between relative coverage ratio of inhibitor on carbon steel surface and inhibition efficiency at 145 °C was obtained as the equation μ = 0.94η, it was a direct proportion. This result proved that the complex inhibitor inhibited the corrosion of carbon steel by geometric blocking effect. When solution temperature was 160 °C, the adsorption Gibbs free energy of PWVA and Sb2O3 on carbon steel were −49.59 and −44.29 kJ mol−1, respectively. It indicated that the adsorption processes of PWVA and Sb2O3 on carbon steel surface were spontaneous processes. As a strong oxidant, PWVA facilitated the compact passive film comprising of FeO, Fe2O3 and Fe3O4 forming on the surface and itself was reduced to heteropoly blue. Sb2O3 adsorbed on carbon steel surface formed an adsorption film. PWVA and Sb2O3 behaved synergistic effect. The corrosion resistance performance of carbon steel in 55%LiBr + 0.07 mol L−1 LiOH solution was improved by PWVA/Sb2O3 complex inhibitor.  相似文献   

13.
This study reports a new, simple and effective pre-calcined method for fabrication BaO–TiO2–B2O3–SiO2 low temperature co-fired ceramics (LTCC) at a sintering temperature below 900 °C, and with dielectric losses (tan δ) lower than 2 × 10−3. The research results have shown that the addition of 2–5 wt% Al2O3 could easily eliminate the porosity of the glass-ceramics because of the excellent wetting behavior between alumina and the BaO–B2O3–SiO2 glass liquid phase in the low temperature co-fired ceramic system.  相似文献   

14.
The hydrolysis of ruthenium alkoxide/titanium tetraethoxide mixtures to gels and powders containing 30–40 mol% Ru was investigated. Basic or neutral conditions led to powders consisting of 2–10 nm diameter crystalline RuO2 nanoparticles embedded in a matrix of crystalline (anatase) and amorphous TiO2. Acid hydrolysis conditions gave gels containing smaller, amorphous RuO2 nanoparticles (1–3 nm). In all samples the RuO2 nanoparticles tended to clump into aggregates up to 0.5 μm across. Acid or neutral hydrolysis of ruthenium ethoxide gave samples which displayed lower surface Ru:Ti ratios as measured by XPS compared to the bulk (XRF), and also contained more low-valent Ru (as measured by XRF), probably due to incomplete hydrolysis of the precursors. These samples also contained more Ru metal after calcination (XRD). Calcination (450 °C) was accompanied by Ru-promoted combustion of organic material and led to crystalline (anatase) TiO2 and TixRu1−xO2 solid solution (rutile phase).  相似文献   

15.
The aim of the present work has been to produce high-dense Si3N4 ceramics by a cheaper pressureless sintering method and then to attain vacuum heat treatment to remove residual grain boundary glass in gaseous form. LiAlO2 was used as a sintering additive rather than using Li2O, since its grain boundary glass is not stable above 1200 °C. LiAlO2 was synthesised from 42% Li2CO3 and 58% Al2O3 powder mix reacting together at 1450 °C for 3 h in a muffle furnace. X-ray analysis showed that 95% LiAlO2 was obtained. LiAlO2 was milled and added to silicon nitride powder as a sintering additive. Hot-pressing and pressureless sintering of LiAlO2 containing Si3N4 compacts were carried out at temperatures between 1450–1750 °C. The sintered samples were vacuum heat-treated at elevated temperatures under high vacuum to remove intergranular glass and to increase refractoriness of Si3N4 ceramics. Scanning electron microscope images and weight loss results showed that Li in grain boundary glass (Li–Al–Si–O–N) was successfully volatilised, and oxidation resistance of the sintered samples was increased.  相似文献   

16.
Zirconia ceramics, mainly of cubic phase, are used in different applications because of their particular electrical and structural properties.

After the forming stage, sintering leads to a material with suitable microstructural characteristics. The sintering process mainly depends on thermal cycle and on starting particle size and its distribution; it also depends on density and the microstructure of green material. Cubic zirconia has a high (2680 °C) melting temperature; however, effective sintering could be observed for temperatures higher than 900 °C (nanoparticles), and it may reach a final density of 96–98% the theoretical value at relative low temperatures.

The objective of this paper is to study the sintering kinetics of stabilized zirconia in its cubic phase with 8% molar of Y2O3 under fast firing rates up to nearly isothermal conditions. Samples were shaped from suspensions dispersed with ammonium polyacrylate by slip casting. Sintering was performed in the temperature range between 1200 °C and 1400 °C. The sintering kinetic process was followed by measuring density as a function of time. A sintering model was applied to fit the experimental data of the first steps of densification. It was observed that sintering obeys the same mechanism in the temperature and time ranges under study, which results in an activation energy of 170 kJ mol−1. Sintering is controlled by Zr cation diffusion, for which a lattice diffusion coefficient of Dl = 8 × 10−12 cm2 s−1 at 1400 °C was found, and the activation energy of the diffusion process was 223 kJ mol−1.  相似文献   


17.
Solid solutions of Bi3(Nb1−xTax)O7 (x = 0.0, 0.3, 0.7, 1) were synthesized using solid state reaction method and their microwave dielectric properties were first reported. Pure phase of fluorite-type could be obtained after calcined at 700 °C (2 h)−1 between 0 ≤ x ≤ 1 and Bi3(Nb1−xTax)O7 ceramics could be well densified below 990 °C. As x increased from 0.0 to 1.0, saturated density of Bi3(Nb1−xTax)O7 ceramics increased from 8.2 to 9.1 g cm−3, microwave permittivity decreased from 95 to 65 while Qf values increasing from 230 to 560 GHz. Substitution of Ta for Nb modified temperature coefficient of resonant frequency τf from −113 ppm °C−1 of Bi3NbO7 to −70 ppm °C−1 of Bi3TaO7. Microwave permittivity, Qf values and τf values were found to correlate strongly with the structure parameters of fluorite solid solutions and the correlation between them was discussed in detail. Considering the low densified temperature and good microwave dielectric proprieties, solid solutions of Bi3(Nb1−xTax)O7 ceramics could be a good candidate for low temperature co-fired ceramics application.  相似文献   

18.
Two main formation routes for thaumasite exist below 15 °C. One is the direct route from C–S–H reacting with appropriate carbonate, sulfate, Ca2+ ions and excess water. The other route is the woodfordite route from ettringite reacting with C–S–H, carbonate, Ca2+ ions and excess water, in which thaumasite arises through the intermediate formation of the solid solution woodfordite. The woodfordite route for thaumasite formation appears to be relatively quicker (although still slow) than the direct route, presumably because with the former the ettringite already has the octahedral [M(OH)6] units that can facilitate the critical change from [Al(OH)6]3− to [Si(OH)6]2− groupings. Both routes are mutually dependent on each other. The presence of magnesium salts can modify the path to thaumasite formation. High pressure might be able to stabilise [Si(OH)6]2− groupings and allow thaumasite to become formed above 15 °C. This possibility is discussed.  相似文献   

19.
This paper presents the optical absorption and luminescence properties of Er3+ doped mixed alkali borosilicate glasses: 59.5SiO2 · 20B2O3 · xLi2O · (20 − x)Na2O · 0.5Er2O3 and 59.5SiO2 · 20B2O3 · xLi2O · (20 − x)K2O · 0.5Er2O3, with x = 0, 4, 8, 12, 16 and 20 mol%. The variations of Judd–Ofelt intensity parameters (Ω2, Ω4, and Ω6), hypersensitive transition intensities, total radiative transition probability (AT), radiative lifetimes (τR), integrated absorption cross-sections (Σ) and stimulated emission cross-sections (σp) as a function of x are discussed in detail. The changes in Ω2 and intensities of hypersensitive transitions are attributed to optical basicity changes in the host glass matrix, which leads to variations in the covalency of the Er–O bond. The luminescence properties are reported for certain transitions, and the emission cross-section is high at x = 8–12 in the case of lithium sodium glass, whereas in lithium potassium glass it is high at x = 8.  相似文献   

20.
Glasses of various compositions in the system (100 − x)(Li2B4O7) − x(SrO–Bi2O3–0.7Nb2O5–0.3V2O5) (10  x  60, in molar ratio) were prepared by splat quenching technique. The glassy nature of the as-quenched samples was established by differential thermal analyses (DTA). The amorphous nature of the as-quenched glasses and crystallinity of glass nanocrystal composites were confirmed by X-ray powder diffraction studies. Glass composites comprising strontium bismuth niobate doped with vanadium (SrBi2(Nb0.7V0.3)2O9−δ (SBVN)) nanocrystallites were obtained by controlled heat-treatment of the as-quenched glasses at 783 K for 6 h. High resolution transmission electron microscopy (HRTEM) of the glass nanocrystal composites (heat-treated at 783 K/6 h) confirm the presence of rod shaped crystallites of SBVN embedded in Li2B4O7 glass matrix. The optical transmission spectra of these glasses and glass nanocrystal composites of various compositions were recorded in the wavelength range 190–900 nm. Various optical parameters such as optical band gap (Eopt), Urbach energy (ΔE), refractive index (n), optical dielectric constant and ratio of carrier concentration to the effective mass (N/m*) were determined. The effects of composition of the glasses and glass nanocrystal composites on these parameters were studied.  相似文献   

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