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1.
《Ceramics International》2017,43(12):9060-9066
In this paper, we prepared lead-free (1-x)BaTiO3-xBi(Zn0.5Ti0.5)O3 (x=0.04, 0.08, 0.10, and 0.14) ceramics by a conventional solid-state reaction technique. Pure perovskite structures and dense microstructures were demonstrated for all the compositions. Interestingly, it was found that the sintering temperature tended to decrease with increasing the Bi(Zn0.5Ti0.5)O3 content. It should be stressed that a low sintering temperature of 1050 °C was utilized for the composition of x=0.14. Moreover, the dielectric permittivity-temperature curve became more flat and the relaxor degree became stronger with the augment in Bi(Zn0.5Ti0.5)O3 content. We also conducted a detailed study on the energy storage performance for all the compositions from 25 °C to 180 °C.We found that relatively temperature-stable energy storage performance could be obtained in the compositions with x=0.08, 0.10 and 0.14 regardless of the evolution of dielectric constant during the test temperature range. In particular, due to a higher field of 12 MV m−1, the discharge energy storage densities of x=0.14 could reach 0.81 J cm−3, 0.80 J cm−3, 0.78 J cm−3, 0.72 J cm−3, and 0.67 J cm−3 with high efficiencies of 94%, 92%, 94%, 88% and 77% at 25 °C, 50 °C, 100 °C, 150 °C, and 180 °C, respectively. All these results demonstrate the (1-x)BaTiO3-xBi(Zn0.5Ti0.5)O3 ceramics are quite promising for temperature-stable energy storage applications.  相似文献   

2.
《Ceramics International》2016,42(3):4452-4461
The objective of the present study is to investigate the effect of sintering temperature on the structural, electrical and electrochemical properties of novel Mg0.5Si2 (PO4) 3 NASICON structured compound prepared via sol gel method. X-ray diffraction was used to study the structural properties such as crystalline phase and lattice parameters of the solid electrolytes. Electrical properties of the compound were measured using impedance spectroscopy while the electrochemical stability was investigated by linear sweep voltammetry. All the sintering temperatures yielded compounds consisted of monoclinic crystalline phase with a space group of P1 21/c1. Lattice parameters for Mg0.5Si2 (PO4) 3 samples increased from the sintering temperature at 700–800 °C but decreased for sintering temperature at 900 °C. The sample sintered at 800 °C showed the highest total conductivity of 1.83×10−5 S cm−1 and the highest value of ions mobility, µ of 6.17×1010 cm2 V−1 s−1 which was attributed to the optimum size of migration channel indicated by its unit cell volume. Linear sweep voltammetry result showed that the Mg0.5Si2 (PO4)3 powder was electrochemically stable up to 3.21 V.  相似文献   

3.
The effects of slow-cooling and annealing conditions on dielectric loss, thermal conductivity and microstructure of AlN ceramics were investigated. Y2O3 from 0.5 to 1.25 mol% at 0.25% increments was added as a sintering additive to AlN powder and pressureless sintering was carried out at 1900 °C for 2 h in a nitrogen flowing atmosphere. To improve the properties, AlN samples were slow-cooled at a rate of 1 °C min−1 from 1900 to 1750 °C, subsequently cooled to 970 °C at a rate of 10 °C min−1 and then annealed at the same temperature for 4 h. AlN and YAG (5Al2O3/3Y2O3) were the only identified phases from XRD. AlN doped with 0.5 and 0.75 mol% Y2O3 had a low loss of <2.0 × 10−3 and a high thermal conductivity of >160 W m−1 °C−1.  相似文献   

4.
《Ceramics International》2016,42(3):4532-4538
The structural, thermal and electrochemical properties of the perovskite-type compound La1−xNdxFe0.5Cr0.5O3 (x=0.10, 0.15, 0.20) are investigated by X-ray diffraction, thermal expansion, thermal diffusion, thermal conductivity and impedance spectroscopy measurements. Rietveld refinement shows that the compounds crystallize with orthorhombic symmetry in the space group Pbnm. The average thermal expansion coefficient decreases as the content of Nd increases. The average coefficient of thermal expansion in the temperature range of 30–850 °C is 10.12×10−6, 9.48×10−6 and 7.51×10−6 °C−1 for samples with x=0.1, 0.15 and 0.2, respectively. Thermogravimetric analyses show small weight gain at high temperatures which correspond to filling up of oxygen vacancies as well as the valence change of the transition metals. The electrical conductivity measured by four-probe method shows that the conductivity increases with the content of Nd; the electrical conductivity at 520 °C is about 4.71×10−3, 6.59×10−3 and 9.62×10−3 S cm−1 for samples with x=0.10, 0.15 and 0.20, respectively. The thermal diffusivity of the samples decreases monotonically as temperature increases. At 600 °C, the thermal diffusivity is 0.00425, 0.00455 and 0.00485 cm2 s−1 for samples with x=0.10, 0.15 and 0.20, respectively. Impedance measurements in symmetrical cell arrangement in air reveal that the polarization resistance decreases from 55 Ω cm−2 to 22.5 Ω cm−2 for increasing temperature from 800 °C to 900 °C, respectively.  相似文献   

5.
《Ceramics International》2015,41(6):7374-7380
Porous magnesium aluminate spinel (MgAl2O4) ceramic supports were fabricated by reactive sintering from low-cost bauxite and magnesite at different temperatures ranging from 1100 to 1400 °C and their sintering behavior and phase evolution were evaluated. The effects of sintering temperature on the pore structure, size and distribution as well as on the main properties of spinel ceramic supports such as flexural strength, nitrogen permeation flux and chemical resistance were investigated. The supports prepared at 1300 °C showed a homogeneous pore structure with the average pore size of 4.42 μm, and exhibited high flexural strength (35.6 MPa), high gas permeability (with nitrogen gas flux of 3057 m3 m−2 h−1 under a trans-membrane pressure of 0.1 MPa) and excellent chemical resistance.  相似文献   

6.
《Ceramics International》2016,42(3):3751-3756
Nanoparticles of potassium bismuth titanate K0.5Bi0.5TiO3 (KBT) with an average particle size of 38 nm were prepared using a stirring hydrothermal method. The pure KBT was obtained in 8 h reaction time instead of 24–48 h for conventional hydrothermal method. X-ray diffraction, Raman spectroscopy and TG analysis were used to check the proportion of hydroxyl group existing into the crude and the calcined KBT. A Hydroxyl group was found to affect the crystallite structure parameters and cell volume. When temperature increases from 25 to 1050 °C, the tetragonal structure presents a c/a ratio which decreases from 1.048 to 1.012. TG analysis and Raman vibration at high frequencies show that c/a is affected by hydroxyl group content below 750 °C and by potassium and bismuth vacancies above this temperature. The ceramic KBT showing a 300 nm size presents an improved εr=780 and a dielectric loss tan δ=0.062 at room temperature. Electric conductivity σac was also lowered to 10−6  m)−1 with an activation energy change at 673 K from 0.35 to 0.605 eV.  相似文献   

7.
Systematic investigation on phase transition, dielectric and piezoelectric properties of (1-x)K0.5Na0.5Nb0.997Cu0.0075O3-xSrZrO3 (x = 0, 0.03, 0.06, 0.09, 0.12, 0.15, abbreviated as KNNC-100xSZ) ceramics was carried out. Due to the coexistence of orthorhombic and tetragonal phase in a wide temperature range, a diffused polymorphic phase transition (PPT) region was achieved in KNNC with x  0.06. KNNC-12SZ ceramics exhibited high dielectric permittivity (∼1679), low dielectric loss (∼0.02) and small variation (Δe'/ε'25 °C  15%) in dielectric permittivity from −78 °C to 237.3 °C. KNNC-6SZ ceramic possessed a high level of unipolar strain (∼0.15%) and maintained a smaller variation of ±12% under the corresponding electric field of 60 kV cm−1 at 10 Hz from 25 °C to 175 °C. d33*, which was calculated according to the unipolar strain at 60 kV cm−1, was 230 pm V−1 and remained stable below 100 °C. Therefore, our work provided a new promising candidate for temperature-insensitive capacitors and piezoelectric actuators.  相似文献   

8.
Transparent Nd:YAG ceramics were fabricated by solid-state reactive sintering of Y2O3, α-Al2O3 and Nd2O3 powders with TEOS and MgO as sintering aids. The powders were ball-milled, dried, sieved and calcined at different temperatures. Samples sintered at 1745 °C for 10 h were utilized to observe the microstructure and the optical transmission. It is found that heat treatments of the powder mixtures above 600 °C for 1 h are necessary to remove the carbon contamination but below 800 °C for 4 h can avoid strong aggregation of the powder. So there is a room for heat-treatment, between 600 °C and 800 °C that can obtain Nd:YAG ceramics with almost pore-free microstructures and high transparency. Highly transparent Nd:YAG ceramic with 84.3% in-line transmission at 1064 nm was fabricated by sintering the 800 °C-1 h-heat-treated powder mixture at 1745 °C for 50 h. Even at wavelength of 400 nm, the transmittance of the sample reached 82.9% and the optical scattering coefficient was as low as 0.71% cm−1.  相似文献   

9.
《Ceramics International》2016,42(14):15664-15670
Sodium bismuth titanate (BNT) nanopowder of molar composition 50/50 (Na0.5Bi0.5TiO3) was prepared by a sol-gel processing method. The structure and microstructure of the precursor gel as well as the ferroelectric, pyroelectric, dielectric and piezoelectric properties of the BNT were studied. BNT crystallized in the rhombohedra perovskites structure Na0.5Bi0.5TiO3 was obtained from the precursor gel by heating at 700 °C for 2 h in air. The BNT ceramic at 1100 °C sintering temperature present high crystallinity, good dielectric properties at 1 kHz (ε′=885, tan δ=0.03, Tc=370 °C), piezoelectric properties (k33=0.39, c33=105 GPa, e33=12.6 C/m2, d33=120 pC/N), high remnant polarization (Pr=47 μC/cm2) and pyroelectric coefficient (p=707 μC/m2 K) and low coercive field (Ec=55 kV/cm). Hence, the BNT prepared by sol-gel method could be used for silicon based memory device application where a low synthesis temperature is a key requirement.  相似文献   

10.
A considerable reduction (≥250 °C) in the sintering temperature, enhancement of the sintering density, and a slight improvement of the electrical properties, can be achieved by using bismuth oxide in the range of 0.2 to 2 wt.%, as a sintering aid for gadolinia-doped ceria (GDC) ceramic electrolytes. Dilatometric experiment (CHR) and SEM observations indicate that a liquid phase-assisting sintering mechanism contributes to the improvement in sintering density for bismuth oxide concentrations exceeding 0.5 wt.%. The addition of small amount of Bi2O3 ≤0.5 wt.% also results in the achievement of highly dense ceramic bodies (≥99% of theoretical density) after sintering at 1200 °C for 4 h, which indicates that the addition of Bi2O3 to gadolinia-doped ceria promoted the sintering process by a cooperating volume diffusion-liquid phase-assisting mechanism. Based on the lattice constant data, the solid solubility limit of Bi2O3 in gadolinia-ceria is, probably, lower than 1.0 wt.%. Grain size also increased with increasing Bi2O3 content up to 0.5 wt.% and then it decreased with further addition of Bi2O3. The addition of the smaller amounts of bismuth oxide, i.e., ≤1.0 wt.% Bi2O3 slightly enhanced the total ionic electrical conductivity of the gadolinia-doped ceria electrolyte. The sintering temperature strongly influenced the electrical conductivity of the doped-GDC ceramics. The best sample was that containing 1.0 wt.% Bi2O3 sintered at 1400 °C for 2 h which had an ionic electrical conductivity of 4 S m−1 at 700 °C, and an activation energy of 0.58 eV for the oxide-ion conduction process in air.  相似文献   

11.
Li2TiO3 is a candidate material for tritium breeding in the future nuclear fusion reactor. In this study, Li2TiO3 powder was synthesized by ultrasonic-assisted solution combustion synthesis (USCS) in a single step. The ultrasonic transducer with the power of 1000 W was introduced in the synthesis process. The crystallite size of Li2TiO3 powder prepared by utilization of ultrasonic power is significantly decreased to ∼5.0 nm, while the one obtained without ultrasonic power is 20.0 nm. Li2TiO3 ceramic sintered from USCS powder at 800 °C exhibits the small grain size of 330 nm and the open pores size of 140 nm. The crush load of the ceramic reaches 37.2 N although the structure is porous. Compared with the ceramic prepared by solid-state reaction and conventional solution combustion synthesis, USCS sample has a higher conductivity of 2.0 × 10−6 S m−1 at room temperature, indicating the lower tritium diffusion barrier in the ceramic.  相似文献   

12.
Lead-free Bi0.5Na0.5TiO3-SrTiO3 incipient piezoceramics with Li2CO3 and MnO2 additives were successfully fabricated at low firing temperature for applications in co-fired multilayer piezoactuators. The addition of Li2CO3 effectively shifted the sintering temperature from 1230 °C down to 1075 °C, where the ceramics were co-fired with a Ag/Pd (75/25) inner electrode. The prototype actuators were prepared by tape-casting method using ceramics with the composition of 0.74Bi0.5Na0.5TiO3-0.26 SrTiO3 + 0.15 wt%MnO2 + 0.45 wt%Li2CO3. The total number of active layers was 13, and each ceramic layer had a thickness of 60 μm. The actuator output a large strain up to ∼0.20% at a driving field of 4 kV/mm, due to the field-induced phase transition between the ergodic relaxor and ferroelectric phases. The excellent voltage-displacement performance of the prototype actuator demonstrates the potential for industrial applications.  相似文献   

13.
The effects of composition, sintering temperature and dwell time on the microstructure and electrical properties of (0.75 ? x)BiFeO3–0.25BaTiO3xBi0.5K0.5TiO3 + 1 mol% MnO2 ceramics were studied. The ceramics sintered at 1000 °C for 2 h possess a pure perovskite structure and a morphotropic phase boundary of rhombohedral and pseudocubic phases is formed at x = 0.025. The addition of Bi0.5K0.5TiO3 retards the grain growth and induces two dielectric anomalies at high temperatures (T1  450–550 °C and T2  700 °C, respectively). After the addition of 2.5 mol% Bi0.5K0.5TiO3, the ferroelectric and piezoelectric properties of the ceramics are improved and very high Curie temperature of 708 °C is obtained. Sintering temperature has an important influence on the microstructure and electrical properties of the ceramics. Critical sintering temperature is 970 °C. For the ceramic with x = 0.025 sintered at/above 970 °C, large grains, good densification, high resistivity and enhanced electrical properties are obtained. The weak dependences of microstructure and electrical properties on dwell time are observed for the ceramic with x = 0.025.  相似文献   

14.
Li2CO3 has been used as a sintering aid for fabricating lead-free ferroelectric ceramic 0.93(Bi0.5Na0.5TiO3)-0.07BaTiO3. A small amount (0.5 wt%) of it can effectively lower the sintering temperature of the ceramic from 1200 °C to 980 °C. Unlike other low temperature-sintered ferroelectric ceramics, the ceramic retains its good dielectric and piezoelectric properties, giving a high dielectric constant (1570), low dielectric loss (4.8%) and large piezoelectric coefficient (180 pC/N). The “depolarization” temperature is also increased to 100 °C and the thermal stability of piezoelectricity is improved. Our results reveal that oxygen vacancies generated from the diffusion of the sintering aid into the lattices are crucial for realizing the low temperature sintering. Owing to the low sintering temperature and good dielectric and piezoelectric properties, the ceramics, especially of multilayered structure, should have great potential for practical applications.  相似文献   

15.
Nanometric-sized gadolinia (Gd2O3) powders were obtained by applying solid-state displacement reaction at room temperature and low temperature calcination. The XRD analysis revealed that the room temperature product was gadolinium hydroxide, Gd(OH)3. In order to induce crystallization of Gd2O3, the subsequent calcination at 600  1200 °C of the room temperature reaction products was studied. Calculation of average crystallite size (D) as well as separation of the effect of crystallite size and strain of nanocrystals was performed on the basic of Williamson-Hall plots. The morphologies of powders calcined at different temperatures were followed by scanning electron microscopy. The pure cubic Gd2O3 phase was made at 600 °C which converted to monoclinic Gd2O3 phase between 1400° and 1600 °C. High-density (96% of theoretical density) ceramic pellet free of any additives was obtained after pressureless sintering at 1600 °C for 4 h in air, using calcined powder at 600 °C.  相似文献   

16.
Lead-free 0.94NBT-0.06BT-xLa ceramics at x = 0.0–1.0 (%) were synthesized by a conventional solid-state route. XRD shows that the compositions are at a morphotropic phase boundary where rhombohedral and tetragonal phases coexist. With increasing La3+ content pyroelectric coefficient (p) and figures of merits greatly increase; however, the depolarization temperature (Td) decreases. p is 7.24 × 10−4C m−2 °C−1 at RT at x = 0.5% and 105.4 × 10−4C.m−2 °C−1 at Td at x = 0.2%. Fi and Fv show improvements at RT from 1.12 (x = 0%) to 2.65 (x10 −10 m v−1) (x = 0.5%) and from 0.021 to 0.048 (m2.C−1) respectively. Fi and Fv show a huge increase to 37.6 × 10−10 m v−1 and 0.56 m2 C−1 respectively at Td at x = 0.2%. FC shows values of 2.10, 2.89, and 2.98 (x10−9C cm−2 °C−1) at RT at 33, 100 and 1000 (Hz) respectively. Giant pyroelectric properties make NBT-0.06BT-xLa at x = 0.2% and 0.5% promising materials for many pyroelectric applications.  相似文献   

17.
The spark plasma sintering (SPS) behaviour of nano-sized Bi4Ti3O12 (BIT) and micron-sized CaBi2Nb2O9 (CBNO) powders is described. The densification process of both powders is very rapid, i.e. the densification occurs within a very narrow time interval (2–3 min using a heating rate of 100 °C min−1 and a pressure of 50 MPa). The BIT powder exhibits a lower densification onset temperature (∼650 °C) and higher maximum shrinkage rate (8.9 × 10−3 s−1 at 780 °C) than that of the CBNO powder (∼825 °C and 4.5 × 10−3 s−1 at 950 °C). Isothermal compaction studies revealed that fully dense nano-sized BIT compacts could be obtained within the temperature region 750 °C < Tiso < 850 °C while for Tiso > 850 °C compacts containing elongated platelet grains are formed. A new preparation route to produce highly textured compacts is described in detail. Appropriate pre-forms are prepared by spark plasma sintering (SPS) and these fully dense compacts are subject to superplastic deformation in the SPS unit to achieve a total compressive strain of ∼60%. This strain was achieved within a period of 1.5 min and with a maximum strain rates of 1.1 × 10−2 s−1 achieved at ∼840 °C and 1.3 × 10−2 s−1 at 1020 °C for the BIT and CBNO compacts, respectively. The X-ray studies showed that the Lotgering orientation factors of grains in the deformed BIT and CBNO compacts are 99% and 70%. The formation of highly textured compacts is suggested to be governed by a superplastic deformation-induced directional dynamic ripening mechanism.  相似文献   

18.
Commercial TiC0.5N0.5 powders were high-energy ball milled for various durations and consolidated without binder using the high-frequency induction heated sintering method (HFIHS). The effect of milling on the sintering behavior, crystallite size and mechanical properties of TiCN powders were evaluated. A nanostructured dense TiCN compact with a relative density of up to 98% was readily obtained within 3 min. The ball milling effectively refined the crystallite structure of TiCN powders and facilitated the subsequent densification. The sinter-onset temperature was reduced appreciably by the prior milling for 10 h from 1170 °C to 820 °C. Accordingly, the relative density of TiCN compact increased as the milling time increases. The microhardness of sintered TiCN was linearly proportional to the density while its toughness did not show any correlation with the crystalline size or density. It is clearly demonstrated that a quick densification of nano-structured TiCN bulk materials to near theoretical density could be obtained by the combination of HFIHS and the preparatory high-energy ball milling processes.  相似文献   

19.
《Ceramics International》2017,43(15):11879-11884
Li6.5La3Zr1.5Nb0.5O12 (LLZN) garnet-type structure was synthesized at low temperature with B2O3 addition by solid state reaction method. The effects of B2O3 content on the formation, microstructure, ionic conductivity and activation energy of the LLZN solid electrolytes have been investigated by X-Ray diffraction (XRD), scanning electron microscopy (SEM) and alternate current (AC) impedance spectroscopy. The cubic LLZN phase was obtained after calcining at 850 °C for 6 h and no phase evolution was observed after sintering at 1100 °C for 6 h. The relative density and lithium ion conductivity increased first and then decreased with increasing B2O3 content, reaching the maximum value of 92.4% and 1.86×10−4 S cm−1 respectively in the sample with 1.4 wt% B2O3. By contrast, the activation energy reached a minimum value of ~31.5 kJ mol−1.  相似文献   

20.
The oxygen permeability of mixed-conducting Sr1−xCaxFe1−yAlyO3−δ (x=0–1.0; y=0.3–0.5) ceramics at 850–1000 °C, with an apparent activation energy of 120–206 kJ/mol, is mainly limited by the bulk ionic conduction. When the membrane thickness is 1.0 mm, the oxygen permeation fluxes under pO2 gradient of 0.21/0.021 atm vary from 3.7×10−10 mol s−1 cm−2 to 1.5×10−7 mol s−1 cm−2 at 950 °C. The maximum solubility of Al3+ cations in the perovskite lattice of SrFe1−yAlyO3−δ is approximately 40%, whilst the brownmillerite-type solid solution formation range in Sr1−xCaxFe0.5Al0.5O3−δ system corresponds to x>0.75. The oxygen ionic conductivity of SrFeO3-based perovskites decreases moderately on Al doping, but is 100–300 times higher than that of brownmillerites derived from CaFe0.5Al0.5O2.5+δ. Temperature-activated character and relatively low values of hole mobility in SrFe0.7Al0.3O3−δ, estimated from the total conductivity and Seebeck coefficient data, suggest a small-polaron mechanism of p-type electronic conduction under oxidising conditions. Reducing oxygen partial pressure results in increasing ionic conductivity and in the transition from dominant p- to n-type electronic transport, followed by decomposition. The low-pO2 stability limits of Sr1−xCaxFe1−yAlyO3−δ seem essentially independent of composition, varying between that of LaFeO3−δ and the Fe/Fe1−γO boundary. Thermal expansion coefficients of Sr1−xCaxFe1−yAlyO3−δ ceramics in air are 9×10−6 K−1 to 16×10−6 K−1 at 100–650 °C and 12×10−6 K−1 to 24×10−6 K−1 at 650–950 °C. Doping of SrFe1−yAlyO3−δ with aluminum decreases thermal expansion due to decreasing oxygen nonstoichiometry variations.  相似文献   

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