Sr0.4Ba0.6Nb2O6物相形成过程的XRD分析

采用X射线衍射技术（Guinier-Hagg相机）分析了Sr0.4Ba0.6Nb2O6（SBN40）原始混合粉料经不同温度煅烧后的相组成，并利用PIRUM程序对不同反应温度下形成铌酸锶钡相的晶胞尺寸进行了计算。结果表明：在Sr0.4Ba0.6Nb2O6的形成过程中将出现中间相Na5Nb4O15、Sr5Nb4O15、SrNb2O6与BaNb2O6，而SrNb2O6与BaNb2O6最终反应生成铌酸锶钡。反应生成的铌酸锶钡的晶胞参数随反应温度的升高而变小。依据这些实验结果，文中提出了Sr0.4Ba0.6Nb2O6相的形成机制。     

Sintering condition and PTCR characteristics of porous (Ba,Sr)(Ti,Sb)O3

We fabricated porous (Ba,Sr)(Ti,Sb)O₃ ceramics by adding potato-starch (1–20 wt %) and investigated the effects of sintering temperature (1300–1450 °C) and time (0.5–10 h) on the positive temperature coefficient of resistivity characteristics of the porous ceramics. The room-temperature electrical resistivity of the (Ba,Sr)(Ti,Sb)O₃ ceramics decreased with increasing sintering temperature, while that of the ceramics increased with increasing sintering time. For example, the room-temperature electrical resistivity of the (Ba,Sr)(Ti,Sb)O₃ ceramics for the samples sintered at 1300 °C and 1450 °C for 1 h is 6.8×10³ and 5.7×10² cm, respectively, while that of the ceramics is 6.5×10² and 1.3×10⁷ cm, respectively, for the samples sintered at 1350 °C for 0.5 h and 10 h. In order to investigate the reason for the decrease and increase of room-temperature electrical resistivity of the samples with increasing sintering temperature and time, the average grain size, porosity, donor concentration of grains (N _d), and electrical barrier height of grain boundaries () of the samples are discussed.     

The influences of rapid-thermal annealing on the characteristics of Sr0.6Ba0.4Nb2O6 thin film

The Sr0.6Ba0.4Nb2O6 (SBN) thin films were successfully prepared on Pt/Ti/Si and SiO2/Si/Al substrates and crystallized subsequently using rapid thermal annealing (RTA) process in ambient atmosphere for 1 min. The surface morphologies and thicknesses of as-deposited and annealed SBN thin films were characterized by field emission scanning electron microscopy, and the thickness was about 246 nm. As compared with the as-deposited SBN thin films, the RTA-treated process had improved the crystalline structures and also had large influence on the crystalline orientation. When the annealing temperatures increased from 700 degrees C to 900 degrees C, the diffraction intensities of (410) and (001) peaks apparently increased. Annealed at 900 degrees C, the (001) peak had the maximum texture coefficient and SBN thin films showed a highly c-axis (001) orientation. The influences of different RTA-treated temperatures on the polarization-applied electric field (P-E) curves and the capacitance-voltage (C-V) curves were also investigated.     

Synthesis and dielectric characterization of Ba0.6Sr0.4TiO3 ferroelectric ceramics

Ferroelectric ceramics Ba_0.6Sr_0.4TiO₃ (BST 40) were prepared, by solid-state reaction in the temperature range 1210-1450 °C. Maximum values of the ceramic densities were around 94% of their theoretical value. X-ray diffraction techniques (XRD) and scanning electron spectroscopy (SEM) were used to analyze the structure and the surface morphology of ceramics. Rounded, well defined or abnormal granular growth was observed in the SEM images, vs. sintering conditions and purity of the raw materials. In all samples, BST 40 ceramic is the major phase, but there are also present small amounts of secondary phases, as revealed in XRD diffraction patterns. Permittivity and dielectric loss measurements were performed in the temperature range − 150 to + 150 °C, and 150 Hz-5 MHz frequency values. Permittivity values rising from 1200 to 12,500, with increasing sintering temperatures, were recorded. Narrow and well defined transition peaks were noticed at higher sintering temperatures. Curie temperature was around 2 °C, for samples with the mentioned composition. Permittivity and losses vs. frequency show different behavior whether BST ceramics are in polar or non-polar state and with the distance toward phase transition. Microwave measurements performed at room temperature have shown lower values of permittivity, compared with similar data at low frequency, and dielectric losses lower than 1% at 0.7 GHz. The sintering conditions (temperatures, sintering time, etc.) and purity of the raw materials lead to important changes of transition temperatures in the polymorphic diagram, which we have built—for the other Ba1−xSrxTiO3 compositions (x = 0.25-0.90) sintered at 1260 °C for 2 h.     

Fibrous growth of tricalcium phosphate ceramics

Structural transformation and sintering processes of tricalcium phosphate (TCP) ceramics prepared from defective hydroxyapatite (Ca9HPO4(PO4)5OH) were studied by X-ray diffraction (XRD) and atomic force microscopy (AFM). Starting powders with Ca/P ratio 1.5 were obtained by adding 0.5 l of 0.3 M H3PO4 solution to an equal volume of 0.45 M Ca(OH)2. In the prepared ceramics, the onset temperature for transformation of defective hydroxyapatite into TCP (witlokite) agrees with the onset temperature for sintering (800 °C). Sintering occurs through the formation of a fibrous structure, which resembles biological hard tissue. In the 1000–1200°C range, these fibres coalesce into grains of up to 0.6 m in size with a fibrous-laminar morphology. At the end of this sintering stage witlokite transforms into TCP. At about 1450°C, partial decomposition of TCP into Ca2P2O7+Ca4P2O9 is observed. AFM observations suggest that Ca2P2O7 is segregated in the liquid state and increases the velocity of grain growth (up to 12 m).     

Effect of sintering temperature on dielectric properties of Ba0.6Sr0.4TiO3–MgO composite ceramics prepared from fine constituent powders

Composite ceramics of Ba_0.6Sr_0.4TiO₃ + 60 wt.% MgO were prepared from fine constituent powders by sintering at 1200–1280 °C. The composite specimens sintered at the relatively low temperatures showed satisfactory densification due to fine morphology of the constituent powders. The elevation of sintering temperature promoted the incorporation of Mg²⁺ into the lattice of the Ba_0.6Sr_0.4TiO₃ phase and grain growth of the two constituent phases. The dependence of the dielectric properties on sintering temperature was explained in relation to the structural evolution. Controlling the sintering temperature of the composite was found to be important to achieve the desired nonlinear dielectric properties. Sintering at 1230 °C was determined to be preferred for the composite in terms of the nonlinear dielectric properties. The specimen sintered at the temperature attained a tunability of 17.3% and a figure of merit of 127 at 10 kHz and 20 kV/cm.     

Low-firing and microwave dielectric properties of Ba[(Ni0.6Zn0.4)0 .33Nb0.67]O3 ceramics doped with Sb2O5 and B2O3

The purpose of this study was to reduce the sintering temperature of Ba[(Ni0.6Zn0.4)0.33Nb0.67]O3 ceramics by doping with Sb2O5 and B2O3. Phase formation and dielectric properties were analyzed using X-ray diffraction and the post resonator method (10 GHz), respectively. It was observed that an addition of 1 mol % Sb2O5 or 1 mol % B2O3 was very effective in reducing the sintering temperature from 1500 to 1300 °C. However, these samples showed a temperature coefficient of resonant frequency far from 0 ppm/°C. The two additions produced a temperature coefficients with opposite signs. The combination of the two dopants produced a temperature coefficient very close to 0 ppm/°C as well as a better quality factor.     

The abnormal grain growth and dielectric properties of (Nb,Ba) doped TiO2 ceramics

The effect of consolidation pressure and crystallite size of powders crystal phases of TiO₂ on sintered microstructure of TiO₂ ceramics doped with 0.25 mol % Nb and 1.0 mol % Ba were investigated. Also, the development sequence of abnormal grain growth of (niobium, barium) doped TiO₂ ceramics was proposed. The second phases of as-sintered surface were determined. The dielectric properties of Ag-electroded samples were correlated with the resistivity of the bulk (Nb, Ba) doped TiO₂ ceramics. Abnormal grain growth lowered the resistivity of bulk material of (Nb, Ba) doped TiO₂ ceramics, and moved the relaxation frequency of fan δ to high frequency region over 10⁵ Hz. Controlling the sintered microstructures can obtain reasonably good dielectric properties.     

Phase Formation and Grain Growth Kinetics of High-Tc Superconducting Tl-1223 Ceramics

The phase formation and grain growth of (Tl,Pb,Bi)(Sr,Ba)₂Ca₂Cu₃O_9– ceramics were investigated in the temperature range between 860°C and 1000°C. It was found that partial melting seems to improve the texture of the samples. The phase purity, however, is limited due to an incomplete re-precipitation process due to the formation of a liquid phase, which is already present above 885°C. The resulting grain growth exponent n, however, appears to differ from the classical exponent of 1/3 for the coexistence of a liquid phase in the temperature range between 885°C and 920°C. For the first time, the activation energy for the high-T_c Tl-1223 phase has been determined showing faster grain growth kinetics than for Y-123 and Bi-2223.     

复相陶瓷 BSTN的相组成和微观结构与 Sr/Ba比的关系

按配方(1-x)BaO·xSrO·0．7TiO2·0．3Nb2O5制备不同Sr／Ba比的钙钛矿／钨青铜复相陶瓷,用XRD和SEM研究其组成和结构与Sr／Ba比的关系．结果表明,改变Sr／Ba比对两相稳定共存没有影响;受同一体系中两相不同固溶能力控制,钙钛矿相中Ba2+和Sr2+之间的置换几率远大于钨青铜相中,其Sr／Ba比随体系Sr／Ba比变化,而钨青铜相的Sr／Ba比维持约0．667基本不变;控制体系Sr／Ba比偏离该值,钙钛矿相的晶格常数相应偏离标准值,而钨青铜相基本不变;提高Sr／Ba比,钙钛矿相晶粒尺寸减小,而钨青铜相变化不明显．两相共存体系中,当两相都可形成固溶体但固溶能力不同时,固溶度大的一相优先参与置换,并抑制另一相的固溶．     

Properties of sol-gel derived strontium barium niobate ceramics and the effect of V2O5 additive

Strontium barium niobate, Sr _x Ba_1–x Nb₂O₆, (SBN) ceramics with a range of Sr/Ba ratios were fabricated using a solution chemistry approach with alkoxides dissolved in acetic acid. Powders obtained from dried gels were calcined at 800°C for three hours, a heat treatment that produced fully crystalline powders. After preparing bulk ceramics from these powders by sintering at 1200°C for 1–24 hours, the tetragonal tungsten bronze (TTB) phase was present in all compositions between 0 x 1, although not predicted by the phase diagram for BaNb₂O₆and SrNb₂O₆. Vanadium pentoxide (V₂O₅) additions increased the densification, the amount of tungsten bronze phase, and the dielectric constant for all compositions except for Sr_0.65Ba_0.35Nb₂O₆(SBN65) ceramics.     

Structure and electrical properties of strontium barium niobate ceramics

SBN, x=0.25, 0.35, 0.50, 0.60 and 0.75 series of ceramics prepared by traditional sintering method have been studied systematically. The impact of composition and sintering temperature on structures, microstructures, and electrical properties of SBN ceramics was characterized of X-ray diffraction, scanning electron microscopy, and electrical measurements. It is found that the composition and temperature play an important role on the fabrication of single phase tetragonal TTB SBN ceramics. At x=0.5, TTB SBN ceramics can be obtained at 1200°C. For x<0.5, it consists of a mixture of TTB structure SBN and orthorhombic phase BaNb₂O₆ even at 1300°C; TTB structure SBN and orthorhombic phase SrNb₂O₆ for x>0.5. The complete TTB phase is produced at 1350°C. With Sr content increasing, the electrical performances show a regular change, strongly conforming to the reducing of the Curie temperature. SBN with the Sr composition of x=0.60-0.75 is a promising candidate for electro-optics device applications.     

Preparation and characterization of perovskite ceramic powders by gelcasting

Perovskite La0.6Sr0.4Co0.8Fe0.2O3– (LSCF) powders have been successfully synthesized from oxide and carbonates based on the principle of gelcasting. Phase-forming temperature is very dependent on the ball-milling process during the suspension preparation. As the ball-milling time is increased, the temperature of phase formation decreases, therefore the perovskite powder obtained has a larger Brunaver–Emmett–Teller (BET) specific surface area. The grain sizes were around 1 m at 1000°C and 2 m at 1100°C from scanning electron microscopy (SEM) photographs. The perovskite powders have good sinterability: the sintering densities of ceramic bodies shaped with as-prepared powders were investigated. SEM photos show that sintered ceramics exhibit a well defined morphology in the packing and sintering of particles. The oxygen permeance of disc shaped samples, with a thickness ranging from 1.02 to 1.98 mm was 6.39 × 10–8–1.99 × 10–8 mol cm–2 s–1 at 900°C indicating that LSCF ceramics have high oxygen permeation. It can be concluded that gelcasting is a simple and effective method for preparing practical multicomponent perovskite powders.     

Effect of partially oxidized Ti powders on the microstructure and PTCR characteristics of (Ba,Sr)TiO3

Rutile TiO₂ (a=4.594 å and c=2.958 å) phase was formed on the outer region of Ti powders after oxidation at 600 °C for 1–300 h. Porous (Ba,Sr)TiO₃ ceramics were fabricated by adding partially oxidized Ti powders (4–8 vol %) into (Ba,Sr)TiO₃ powders, and showed excellent positive temperature coefficient of resistivity (PTCR) characteristics after paste-baking treatment at 580 °C in air. The PTCR characteristics of the porous ceramics were mainly attributed to the adsorption of oxygen at the grain boundaries. The microstructure and electrical properties of the porous (Ba,Sr)TiO₃ ceramics containing the partially oxidized Ti powders oxidized at 600 °C for different oxidation times (1–300 h) were investigated.     

Evolution of the microstructure of undoped and Nb-doped SrTiO3

Undoped and Nb-doped SrTiO₃ specimens with excess titania compositions were prepared by sintering in air at 1420 or 1480 °C. Large grains due to liquid-phase sintering were obtained for undoped specimens containing 0.6 mol % excess titania and fired at 1480 °C. On the other hand uniform fine grains were observed for samples fired at 1420 °C, resulting from grain-growth inhibition due to exsolved TiO₂ second phase. The solubility of excess titania seemed less than 0.2 mol% under our experimental conditions. The microstructural behaviour of Nb-doped SrTiO₃ could be explained well by the Sr-vacancy compensation model. According to this model, the solubility of excess titania in SrTiO₃ increased with Nb₂O₅ dopant concentration. Thus, for specimens which had high excess titania compositions and were sintered at 1480 °C, large grains were observed when the Nb content was low enough to retain sufficient excess titania-forming liquid phase. For specimens having the same compositions and fired at 1420 °C, uniform fine grains were obtained due to grain growth inhibition by the exsolved TiO₂ second phase, when the Nb content was low. If the excess titania was less than the solubility determined by the amount of Nb dopant, Ruddlesden-Popper-type phases were believed to be formed and resulted in poor densification. Although excess titania was the major factor in determining the grain size of the specimens, the niobium dopant enhanced grain growth.     

New high permittivity and low loss ceramics in the BaO–TiO2–Nb2O5 composition

New dielectric ceramics with formula BaTi3Nb4O17 and Ba6Ti14Nb2O39 have been prepared and characterized. BaTi3Nb4O17 was densified to 92% of TD after firing at 1310 °C for 4 h. However, Ba6Ti14Nb2O39 fired under optimized conditions (1260 °C for 4 h) showed only 85% TD together with secondary phase. The crystal system of both of the compositions is orthorhombic. The BaTi3Nb4O17 has r56, Qu2100 (at 4.402 GHz), f+86 p.p.m. K-1 and Ba6Ti14Nb2O39 as r50, Qu650 (4.359 GHz) and f+165 p.p.m. K-1. © 1998 Kluwer Academic Publishers     

Ultralow expansion ceramics in the HfO2-TiO2 system synthesized by an hydrolysis and polycondensation technique

Ultra-refractory ceramics from the HfO₂-TiO₂ system in the range 30–40 mol% TiO₂, with a near-zero thermal expansion, have been synthesized by hydrolysis and polycondensation of titanium alkoxide and hafnium dichloride alcoholic solutions and sintered at moderate temperature. Thermal stability, crystallization, density and microstructure of these materials have been examined. The as-prepared powder, amorphous at room temperature, crystallized quickly when heated at 500 ° C. Entire crystallization occurred after treatment at 1000 °C. Sintering at 1500 °C on cold-pressed samples led to ceramics with weak porosity (7%), low expansion coefficient <1×10^–6 °C^– with a minimum for 30 mol% TiO₂ content. SEM examination on sintered materials at 1500 °C reveals a grain size from 2–6 m, increasing with TiO₂ content.     

Solid state synthesis and properties of monoclinic celsian

Monoclinic celsian of Ba0.75Sr0.25Al2Si2O8 (BSAS-1) and Ba0.85Sr0.15Al2Si2O8 (BSAS-2) compositions have been synthesized from metal carbonates and oxides by solid state reaction. A mixture of BaCO3, SrCO3, Al2O3, and SiO2 powders was precalcined at 900–940 °C to decompose the carbonates followed by hot pressing at 1300 °C. The hot pressed BSAS-1 material was almost fully dense and contained the monoclinic celsian phase, with complete absence of the undesirable hexacelsian as indicated by X-ray diffraction. In contrast, a small fraction of hexacelsian was still present in hot pressed BSAS-2. However, on further heat treatment at 1200 °C for 24 h, the hexacelsian phase was completely eliminated. The average linear thermal expansion coefficients of BSAS-1 and BSAS-2 compositions, having the monoclinic celsian phase, were measured to be 5.28 × 10–6 °C–1 and 5.15 × 10–6 °C–1, respectively, from room temperature to 1200°C. The hot-pressed BSAS-1 celsian showed room temperature flexural strength of 131 MPa, elastic modulus of 96 GPa and was stable in air up to temperatures as high as 1500 °C.     

High-power piezoelectric characteristics of textured bismuth layer structured ferroelectric ceramics

Abstract-The high-power piezoelectric characteristics in h001i oriented ceramics of bismuth layer structured ferroelectrics (BLSF), SrBi(2)Nb(2)O(9) (SBN), (Bi,La)(4)Ti(3)O(12) (BLT), and CaBi(4)Ti(4)O(15) (CBT), were studied by a constant voltage driving method. These textured ceramics were fabricated by a templated grain growth (TGG) method, and their Lotgering factors were 95%, 97%, and 99%, respectively. The vibration velocities of the longitudinal mode (33-mode) increased proportionally to an applied electric field up to 2.5 m/s in these textured BLSF ceramics, although, the vibration velocity of the 33-mode was saturated at more than 1.0 m/s in the Pb(Mn,Nb)O(3)-PZT ceramics. The resonant frequencies were constant up to the vibration velocity of 2.5 m/s in the SBN and CBT textured ceramics; however, the resonant frequency decreased with increasing over the vibration velocity of 1.5 m/s in the BLT textured ceramics. The dissipation power density of the BLT was almost the same as that of the Pb(Mn,Nb)O(3)-PZT ceramics. However, the dissipation power densities of the SBN and CBT were lower than those of the BLT and Pb(Mn,Nb)O(3)-PZT ceramics. The textured SBN and CBT ceramics are good candidates for high-power piezoelectric applications.     

Combustion synthesis of Sr0.5Ba0.5Nb2O6 and effect of fuel on its microstructure and dielectric properties

Nano-sized Sr_0.5Ba_0.5Nb₂O₆ (SBN50) powder has been synthesized, at very short reaction time, for the first time by a novel combustion method. Ba(NO₃)₂ and Sr(NO₃)₂ were used as source of Sr and Ba, respectively, while Nb-oxalate was used as the source of niobium. Urea, hexamethyltetramine (HMT) and glycine were used as fuel. The crystallite sizes in the powder ranged between 14-125 nm. X-ray diffraction analysis showed complete SBN50 phase formation at 700 °C, when urea/HMT was used as fuel, and at 800 °C when glycine was used as fuel. Ferroelectric-paraelectric phase transition temperature (T_c) close to 40 °C was observed when urea and HMT were used and the T_c was −49 °C when glycine was used. When urea was used as fuel highest dielectric constant was observed for the pellets sintered at 1250 °C for 4 h. Low dielectric loss was observed when HMT was used as fuel. Larger grain sizes in the sintered pellets were observed when glycine was used as fuel.