Mn和Zr共掺杂钛酸锶钡/氧化镁复合陶瓷材料的微结构和介电性能

通过固相反应法制备Mn、Zr共掺杂钛酸锶钡/氧化镁陶瓷粉体,经干压成型后在空气气氛中于1450℃烧结4h,通过扫描电子显微镜和X射线衍射研究了ZrO2和MnO2共掺杂的Ba0.6Sr0.4TiO3/MgO复合陶瓷材料的微结构和介电性能。结果表明:ZrO2可以显著降低材料的介电常数和介电损耗,有效提高了陶瓷材料的温度稳定性;随ZrO2添加量的增加,体系的晶胞参数略有增加,MgO在钛酸锶钡中以独立相的形式存在;制备出的BST铁电陶瓷材料的25℃相对介电常数较低(εr<110),介质损耗小于1.0×10–3(在频率为10kHz时),温度系数小于6.012×10–3,可调性大于20%(8.0kV/mm),适用于制作移相器。     

Highly porous barium strontium titanate (BST) ceramic foams with low dielectric constant from particle‐stabilized foams

A novel method for fabrication of highly porous barium strontium titanate (BST) ceramic foams based on particle‐stabilized foaming method was developed for the first time, in which propyl gallate (PG) was employed as BST particle modifier. The results showed that the stability of wet BST foams closely depends on the pH value and PG concentration, which could be explained by the adsorption behavior of PG on BST particle surface. BST ceramic foams with dense, uniform, and closed pore and defect‐free wall were obtained. The pore size and porosity can be well controlled by adjusting solid loading and sintering temperature. It was revealed that not only sintering temperature but also solid loading significantly influenced the growth of BST grain. The BST ceramic foams exhibited high porosity in the range of 81%‐95%, low dielectric constant in the range of 47‐150, and low dielectric loss below 0.0025. The BST ceramic foams with higher porosity presented a tendency of lower dielectric constant and the fitting results indicated that the natural logarithm of dielectric constant was linear correlated with porosity.     

0-3型钛酸锶钡与聚四氟乙烯复合材料的冷烧结制备与介电性能研究

0-3型钛酸锶钡(BST)与聚四氟乙烯(PTFE)复合材料是一种新型的陶瓷/高聚物功能复合材料,可以兼具BST材料与PTFE材料的优点,可表现出较高的介电常数和介电可调性。但是受聚合物相介电常数低的限制,常规方法(流延法)制备的以聚合物为基体,以陶瓷为填充相的复合材料的介电常数基本在100以下。为了进一步提高BST/PTFE复合材料的介电性能,本研究采用一种新型烧结工艺——冷烧结工艺实现BST陶瓷与PTFE高聚物的共烧。在试验中以BST为基体,引入体积比例为5%的PTFE,并引入固相八水合氢氧化钡(Ba(OH)₂·8H₂O)作为过渡液相以辅助烧结过程进行,制备0-3型BST/PTFE复合材料,并探究了不同冷烧结条件下复合材料的介电性能。结果表明,复合材料样品在冷烧结温度为275 ℃,压力为200 MPa,时间为2.5 h的条件下,介电常数可达到500以上(25 ℃,1 kHz)。相对于常规制备工艺,冷烧结工艺制备出的复合材料的介电常数有很大改进,这对陶瓷/高聚物功能复合材料的低温制备与研究有一定参考意义。     

Role of Domain Processes in Polycrystalline Barium Titanate

The theory of magnetic domains is reviewed and a comparison is made with the ferroelectric case. The known facts regarding domain processes in barium titanate are summarized and an attempt is made to apply these facts to the formulation of mechanisms for several electrical processes in ceramic barium titanate. It is suggested that the initial (low alternating field) dielectric constant of the material is due mainly to induced polarization, with some contribution (about 20%) from 90° domain wall motion, a mechanism which makes a much larger contribution to the dielectric losses at 1000 cycles. The poling process (to make the material piezoelectrically active) is visualized as a removal of 180° domain walls, with only a temporary motion of 90° domain walls. The aging process is thought to be due to the removal from the dielectric polarization of the contribution of the 90° wall motion.     

Direct and indirect measurement of large electrocaloric effect in barium strontium titanate ceramics

Barium strontium titanate (Ba_1-xSr_xTiO₃-BST) ceramics, where x = 0.05, 0.15, 0.25, and 0.35, was prepared via a solid-state reaction method. The lattice structures and morphologies of the ceramic samples were analyzed using X-ray diffraction and scanning electron microscopy technologies. The dielectric and ferroelectric properties of the BST ceramics were characterized using a precision impedance analyzer and a ferroelectric polarization-electric field (P-E) hysteresis loop tester, respectively. The electrocaloric effect was indirectly calculated using the Maxwell relations and P-E loops as a function of temperature and electrical field, and also directly measured using a computer-controlled thermocouple and high-voltage power supply. An adiabatic temperature change of 1.82 K was procured, indicating a promising potential in the applications as cooling devices.     

Ba0.6Sr0.4TiO3-Mg2TiO4复合陶瓷材料的介电可调性及微波特性

采用常规的陶瓷工艺方法制备了Ba0.6Sr0.4TiO3-Mg2TiO4(BST-MT)复合陶瓷材料,并对其相结构、介电以及可调性和微波特性进行了研究.X射线衍射和介电温度特性测试结果表明,BST-MT复合陶瓷具有BST和MT两相结构,非铁电相MT的增加降低了其铁电性,使其介电常数和介电损耗减小.介电偏压和微波性能测试结果表明,BST-MT复合材料仍能保持较高的可调性,且微波性能得到了明显改善.样品30%BST-70%MT(质量分数)在10 kHz下的介电常数为78,介电损耗为0.000 6,在外加3 kV/mm偏置电场作用下,可调性达到25%,在3.714 GHz频率下的介电损耗为0.0145.     

Dielectric and microwave properties of barium strontium titanate (BST) thick films on alumina substrates

The dielectric and microwave properties of barium strontium titanate (BST) thick films on alumina substrates have been investigated. The BST films were screen printed and sintered at temperatures below 1300 °C. At temperatures below the Curie point the BST films exhibit tunability in the range 15–35% under a DC bias field of 2 kV/mm. The dielectric loss is critically dependent on film thickness with lower losses (<10⁻²) for the thicker films (>100 μm). A relaxation process appears to take place for the BST films in the MHz to GHz frequency regime. The variation of permittivity with bias field exhibits hysteretic behaviour in both the ferroelectric and paraelectric regions. This is believed to arise due to the non-uniform composition and existence of micro/nano-polar phases in the films.     

DC field effect on dielectric property of Ba(ZrxTi1−x)O3 ceramics

Barium zirconate titanate Ba(Zr_xTi_1?x)O₃ (BZT) ceramics have been fabricated by conventional solid state route. The dielectric properties and ferroelectric relaxor behavior were investigated as a function of Zr content and DC bias field. It was found that the relaxor behavior of BZT is enhanced with the increase in Zr content. The temperature of maximum dielectric peak (T_m) of BZT ceramic is greatly increased with DC bias field (E) up to a certain threshold field E_t, below which T_m starts to increase gradually. This behavior could be associated with the size of domain. The relationship between temperature and dielectric tunability is also discussed in details.     

二氧化硅掺杂钛酸锶钡陶瓷的介电性能与电卡效应

采用传统的固相反应法制备二氧化硅（SiO₂）掺杂钛酸锶钡（Ba_0.65Sr_0.35TiO₃,BST）陶瓷（BST+x%SiO₂）,研究了掺杂二氧化硅对BST陶瓷的物相、微观形貌、介电性能及电卡效应的影响。结果表明：掺杂二氧化硅并未改变BST陶瓷的晶型结构,但有助于提升晶粒的均匀性和材料介电性能频率的稳定性。随着二氧化硅掺杂量增加,BST陶瓷的介电常数呈现单调递减趋势,介电弥散特性逐渐增强。二氧化硅的掺杂有利于提升BST陶瓷的电卡性能,其中BST+3%SiO₂陶瓷具有最优的电卡效应,在30 ℃下可获得最大电卡绝热温变（ΔT_max）,ΔT_max和ΔT_max/ΔE分别为1.6 ℃、8.00×10 ^-7 ℃·m/V,电卡效应半峰宽（T_span）为10 ℃左右。     

Effect of Additives on the Crystallization Kinetics of Barium Strontium Titanate Glass–Ceramics

Barium strontium titanate (BST) has been targeted as one potential ferroelectric glass–ceramic for high-energy density dielectric materials. Previous testing has shown that the dielectric constant of these materials was as high as 1000 and the dielectric breakdown strength up to 800 kV/cm. This did not, however, result in exceptional energy density (∼0.90 J/cc). In order to increase overall energy density refining agents can be added to the melt, but the nucleation and growth of the ceramic particles can also play a role. Therefore, in this study the crystallization kinetics were studied to more fully understand how BST phase forms so that the optimal energy density could be obtained. It was determined that the activation energy of the crystallization of BST 70/30 glass–ceramic is approximately 430 kJ/mol which is close to the dissociation energy of Si–O bonds. The Avrami parameter was found to be ∼3 meaning that three-dimensional growth is dominant and the mechanism of growth was interface controlled.     

A Modified Barium Titanate for Capacitors

The modified barium titanate ceramic Ba_0.80Pb_0.20 (Ti_0.88Zr_0.12) O₃ doped with 0.8 mol% CaO and 1 mol%ZrO₂ was prepared. Investigation of the electrical and dielectric properties shows that the material has a room-temperature dielectric constant of 3550 with a variation of 5.7% in the temperature range 10° to 60°C, a loss factor of 0.005, a dc resistivity 1.3 × 10¹²Ω-cm, and a linear variation of resistivity in the log (resistivity) vs temperature plot. This material is a good choice for the fabrication of ceramic capacitors.     

The effect of barium titanate ceramic loading on the stress relaxation behavior of barium titanate-silicone elastomer composites

The stress relaxation behavior of barium titanate (BTO)-elastomer (Ecoflex) composites, as used in large strain sensors, is studied using the generalized Maxwell-Wiechert model. In this article, we examine the stress relaxation behavior of ceramic polymer composites by conducting stress relaxation tests on samples prepared with varying the particle loading by 0, 10, 20, 30, and 40 wt% of 100 and 200 nm BTO ceramic particles embedded in a Ecoflex silicone-based hyperelastic elastomer. The influence of BTO on the Maxwell-Wiechert model parameters was studied through the stress relaxation results. While a pristine Ecoflex silicone elastomer is predominantly a hyperelastic material, the addition of BTO made the composite behave as a visco-hyperelastic material. However, this behavior was shown to have a negligible effect on the electrical sensing performance of the large strain sensor.     

Recent Materials Characterizations of [2D] and [3D] Thin Film Ferroelectric Structures

A review is given of ceramic and single-crystal thin film ferroelectric oxides, emphasizing perovskite phases, together with some new developments on hafnia films. It is shown that single-crystal barium titanate films behave as bulk down to at least 77 nm, with no finite size effects, no phase transition temperature shifts, and no dielectric peak broadening or change from first- to second-order transitions, suggesting that the gradient defect model of Bratkovsky and Levanyuk correctly describes such effects as extrinsic in experimental studies of equally thin ceramic thin films. In ceramic barium–strontium titanate (BST) thin films, it is shown that there is also no intrinsic broadening or shifts in phase transitions, with sharp, unshifted, bulk-like transitions observed only as re-entrant upon warming from cryogenic temperatures; this shows that phase transitions in ceramic thin films are dominated by kinetics and not thermodynamics and are definitely not equilibrium measurements. At high fields (>1 GV/m), the films exhibit space charge-limited conduction; no variable-range hopping is observed, contrary to recent studies on SrTiO₃. Some novel, unconventional switching processes are discussed, comparing the "perimeter effect" (non-equilibrium, ballistic) with Molotskii's equilibrium model. Theory and experiment are described for [3D] nanotubes, nanorods, and nano-ribbons (or micro-ribbons). The layered-structure-perovskite–pyrochlore conversion in bismuth titanate is described together with the PbO+TiO₂ phase separation in lead zirconate titanate during electrical breakdown, as are novel HfO₂ precursors that demonstrate enhanced temperature crystallization from the amorphous state and hence commercial advantages for front-end processing.     

Optical and Microstructural Variations with Electric Field in Barium-Strontium Titanate Ceramics

Quasi-thin sections of large-grained ferroelectric barium-strontium titanate ceramic compositions were observed under crossed polars. Dielectric constant and light transmission were measured as a function of temperature and applied dc voltages. Microscopic observations, such as changes in structure and in optical anisotropy with temperature and simultaneously applied electric fields, are described. Optical data indicate that static electric fields readily induce anisotropy in the isotropic grains at the ferroelectric to paraelectric transition of the ceramic. Below the transition temperature, the effect of the field on the optical and dielectric properties diminishes. Contrary to single-crystal barium titanate, a field-produced reorientation of domains in the ceramic at temperatures below the transition proceeds with difficulty, and is sometimes achieved only after long exposures to high-biasing fields.     

Electrical energy density and dielectric properties of poly(vinylidene fluoride-chlorotrifluoroethylene)/BaSrTiO3 nanocomposites

A series of poly(vinylidene fluoride-chlorotrifluoroethylene) (P(VDF-CTFE))/barium strontium titanate (BST) nanocomposites were fabricated by solution casting method. The addition of BST nanoparticles could enhance both the dielectric constant and the displacement of the resultant composite significantly. The surface activation of BST nonaparticles with KH550 was confirmed as an effective way to improve the breakdown strength of the composite. The high electric displacement (D > 15 μC/cm²), breakdown field (>200 MV/m) and low dielectric loss in P(VDF-CTFE)/BST nanocomposites suggest that the high electrical energy density may be desirable. That indicates the potential application of this class of copolymer/ceramics nanocomposites for high energy storage components.     

Tunable microwave devices using low-sintering-temperature screen-printed barium strontium titanate (BST) thick films

A tunable microwave phase shifter composed of a low-sintering-temperature, screen-printable barium strontium titanate (BST) film and silver metallization was fabricated on an alumina substrate and co-fired at 900 °C for 3 h. The dielectric properties of the films were characterized in a frequency range of 0.8–8 GHz using scattering parameter measurements and a quasi-static coplanar waveguide transmission line model. The temperature dependency of the films was measured through capacitance measurements in a frequency range of 0.5–2.5 GHz. The figure of merit (phase shift/dB of insertion loss) of the phase shifter was found to be 14.6 at 3 GHz with an applied bias field strength of 2.5 V/μm. The performance of the phase shifter is briefly discussed and compared with other phase shifters fabricated by direct screen-printing of BST films.     

Predicting dielectric tunability of compositionally-graded barium strontium titanate thin films on metal substrates by thermodynamic modeling

Dielectric properties of compositionally-graded barium strontium titanate (BST) thin films respectively on Ti and stainless steel (SS) plates were computed using a modified thermodynamic model. Calculated results predict that higher dielectric constant and tunability can be obtained when the films are onto Ti substrates, which have smaller thermal expansion coefficient (TEC). For Ti substrates, “up-graded” films (Ba/Sr ratio increases from substrate to surface) exhibit higher tunability than “down-graded” films; whereas “up-graded” films on SS plates have relatively lower tunability. The received larger dielectric constant and tunability are because of smaller total out-of-plane polarization, which is resulting from smaller total compressive strain. The calculated dielectric constant and tunability of such graded films are in accordance with those of the films fabricated via sol-gel approaches, indicating that the dielectric behavior of ferroelectric films can be adjusted by designing compositional gradient.     

Ferroelectric Phase Transition,Interfaces Quality,and Stress Evolution of TiOx/BaxSr1−xTiO3 Structures

Ba(Sr,Ti)O₃ material presents a remarkable property that lies in the possibility to change the permittivity by applying a dc electric field, i.e., BST is a tunable material. That makes BST a very interesting material for the development of reconfigurable devices in microelectronics. In this study, we focus our work on Ba(Sr,Ti)O₃ with Ba/Sr = 30/70, the films are deposited by radio‐frequency magnetron sputtering on Al₂O₃ (0001). A buffer layer of TiO_x is used to control the film orientation. The influence of this buffer layer on the dielectric properties, the interfaces quality with respect to the film thickness, and the temperature is analyzed. An increase of 30% of the relative permittivity was measured and a tunability of 50% was attained at 300 KV/cm. The dielectric measurements on BST/TiO_x as a function of the temperature show a shift of the Curie temperature (T_c = ?40°C) in comparison to BST without TiO_x layer (T_c = ?80°C). We demonstrate that the Curie temperature does not correspond to the maximum permittivity. The important stress measured on the films (930 MPa) could explain this behavior.     

Complex piezoelectric, elastic, and dielectric coefficients of La-DOPED 0.93 Pb(Mg1/3Nb2/3)O3:0.07 PbTiO3 under DC bias

Complex material parameters (piezoelectric coefficient d₃₁, elastic s₁₁^E, and the dielectric constant K₃₃) of the relaxor ferroelectric ceramic (1-x) Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃(x =.07) with 1% La (lanthanum) were measured as a function of bias field using a bar resonator. The values of the dielectric and piezoelectric phase angles are found to be comparable (i.e., around 0.04 for a d.c. bias field of 2.5 kV/cm), while the elastic phase angle is an order of magnitude smaller (0.001 for the same d.c. bias). For comparison of complex material parameters found from bar resonators, a sample in the form of a small disk is used to measure Poisson's ratio as well as the real components of the piezoelectric and elastic coefficients as a function of bias field.     

Intensification of barium titanate capacitor ceramics sintering assisted by chemically deposited metals

Sintering of barium titanate ceramics, assisted by copper and nickel deposited from solution, is studied. The dielectric constant as a function of temperature is measured for ceramic specimens treated for various periods of time with metal salt solutions. Chemically deposited copper is shown to accelerate sintering without impairing the dielectric properties of the ceramics.Translated from Steklo i Keramika, No. 11, pp. 20–22, November, 1996.