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。     

掺杂Y2O3对钛酸锶钡陶瓷微观结构和介电性能的研究

用固相法制备了制备Ba0.75 Sr0.25 TiO3陶瓷.研究发现,当Y2 O3掺杂量在0.8％以内时,样品均为四方钙钛矿结构.同时,适量的Y2O3掺杂有利于提高材料的介电常数,降低材料的介电损耗.当烧结温度为1260℃,Y2O3掺杂量为0.1％时,BST的样品的相对密度为95.4％,介电常数达最大值,为4730,其介质损耗为0.00237.而Y2O3掺杂量为0.6％时样品的高频稳定性较好.     

烧结温度对钛酸锶钡陶瓷性能的影响

通过微波水热法制备了纳米钛酸锶钡粉体,然后采用不同的烧结温度条件,研究在温度变化的条件下,钛酸锶钡陶瓷的物相、密度、微观形貌以及介电常数。结果表明,随烧结温度升高,材料的致密度逐步提高,而材料的介电系数则与温度的变化并未形成线性变化的关系,与材料的晶粒大小也有一定的关系。因此,可通过对材料组成和烧结温度的调控,制备系列不同介电常数的钛酸锶钡陶瓷。     

改性钛酸锶/PVDF复合材料介电性能研究

采用具有强络合能力的酒石酸在碱性溶液中对SrTiO3陶瓷颗粒进行表面改性,将改性后的SrTiO3颗粒与聚偏二氟乙烯(PVDF)经热压共混成型,制备出系列陶瓷/聚合物基复合材料,对改性SrTiO3/PVDF复合材料进行了介电性能分析。结果表明:添加了改性SrTiO3的复合材料比未改性SrTiO3复合材料的介电常数增加值达34%以上,同时,改性复合材料的介电损耗仍保持较低水平;随着改性SrTiO3在复合材料中含量的增加,介电常数也随之增加,介电损耗仍保持不变,改性后的陶瓷/聚合物复合材料表现出优异的综合介电性能。     

锆钛酸钡二元陶瓷的制备及其介电性能

研究了不同Zr/Ti原子数比下锆钛酸钡二元陶瓷的晶格结构与介电性能。试样的制备采用传统的固相法,经1 300℃保温2.0 h获得烧结良好的陶瓷试样。试验结果显示:随着Ba(ZrxTi1-x)O3体系中Zr含量的增加,晶格常数a增加,晶体四方性降低,Zr的引入还抑制了离子空穴的生成,介质损耗因此降低;经XRD衍射分析表明,在Ba(ZrxTi1-x)O3化合物中x在0.25~0.35变化范围内,试样中存在立方顺电与四方铁电的准同相界。     

气氛烧结钛酸锶钡陶瓷微观组织结构研究

钛酸锶钡(BST)是钛酸锶(SrTiO3)固溶于钛酸钡(BaTiO3)而形成的固溶体,经高温烧结后的陶瓷,出现了晶粒大小不一、组分不均匀、晶界较多的状况,且常常夹杂着玻璃相和气孔相,而这些都会对其电性能造成影响.因此文章拟通过气氛烧结来改善陶瓷材料的微观组织,挖掘其性能潜力.通过选择优化后的烧结温度1420℃烧结的B ...     

钛酸铋钠基陶瓷的冷烧结制备及介电性能

冷烧结(CSP)工艺是近年来新兴的一种高效、节能的材料方法。本工作采用CSP工艺,制备出致密度不低于97%的(1–x)BNT–x NN电介质陶瓷。研究了CSP工艺和Na Nb O₃含量对(1–x)BNT–x NN复相陶瓷的密度、相结构、显微形貌和介电性能的影响。结果表明：CSP工艺由于烧结温度低、保温时间短,可以显著降低晶粒尺寸,有效抑制Bi、Na等元素挥发,从而提高介电常数,降低介电损耗。随着Na Nb O₃含量的增加,(1–x)BNT–x NN复相陶瓷的剩余极化强度显著降低,并且介电常数的温度稳定性显著提升。当x=0.3时,0.7BNT–0.3NN陶瓷样品在25℃至400℃宽温范围内介电常数的变化率小于±6%,介电损耗小于5%,这表明CSP技术制备的(1–x)BNT–x NN陶瓷有望应用于温度稳定性陶瓷电容器。     

锆莫来石材料反应烧结过程的研究

本文利用XRD、SEM和EDAX等方法系统研究了含ZrO_2约33%的ZrO_2-Al_2O_3-SiO_2系耐火材料,从生坯煅烧至1600℃所发生的结晶相变化,显微结构变化及烧结过程中ZrSiO_4的分解温度.结果表胆:ZrSiO_4的分解比莫来石的形成要快,莫来石是由ZrSiO_4分解的非晶SiO_2与Al_2O_3反应形成的.1450～1550℃是锆莫来石耐火材料煅烧过程中物相变化最激烈的温度范围,该反应对致密化产生不利影响.要使结构致密,烧成温度必须大干1600℃.     

Model for the cold sintering of lead zirconate titanate ceramic composites

A model was developed to describe the cold sintering process (CSP) of lead zirconate titanate (PZT) using moistened lead nitrate as a sintering aid. The densities of PZT powder with different volume fractions of lead nitrate were evaluated after cold sintering at 300°C and 500 MPa for 3 hours. The densities were categorized into three zones. In zone I, the relative density following cold sintering increases from 66% to 80%, as the lead nitrate contents rise from 0 to 14 vol%. In this case, the lead nitrate acts to fill some of the pore volume between PZT grains. Zone II serves as a transition region, where there is both pore filling and dilution of the PZT grains associated with lead nitrate contents from 14 to 34 vol%. In zone III, the relative density drops due to dilution at lead nitrate contents exceeding 34 vol%. To slow the process down so that the kinetics could be studied more readily, samples were cold sintered at room-temperature and 500 MPa. It was found that during the first few seconds of compaction, 85PZT/15Pb(NO₃)₂ rapidly densified from 51% to 61% relative density due to particle re-arrangement. For longer times at pressure, the CSP improved the packing relative to PZT compacted without the lead nitrate, yielding a higher relative density. The late stages of the PZT/Pb(NO₃)₂ CSP could be well described using a viscous sintering model for pressures from 50 MPa to 1000 MPa and temperatures from 25°C to 300°C.     

Effect of strontium doping on structural and dielectric behaviour of barium titanate nanoceramics

ABSTRACT

Barium strontium titanate (Ba_(1?x)Sr_xTiO₃ where, x?=?0.0, 0.2, 0.3, 0.4 and 0.5) nanoparticles have been successfully synthesised by sol–gel method and characterised thoroughly. With the increase in Sr concentration (x?>?0.3), the symmetry of the crystal structure changed from tetragonal to cubic phase. The dielectric behaviour of the ceramic nanoparticles was evaluated using impedance analyser with an operating frequency of 1?Hz to 1?MHz. A very high dielectric constant 4915 was obtained for Ba_0.7Sr_0.3TiO₃ at 1?Hz frequency with low dielectric loss of 1.91, which showed very good value than the one previously reported. The density of the material was found to be >98% of theoretical density. Dielectric constants were measured by varying the temperature from 35 to 150°C and the Curie temperatures were also evaluated. The small amount of Sr doping was beneficial for obtaining high dielectric constant material which can be used in various electronic applications.     

Comparison of different sintering aids in cold sinter-assisted densification of lead zirconate titanate

Ceramics such as lead zirconate titanate (PZT) tend to dissolve incongruently, and thus pose a challenge in the cold sintering process. Moist lead nitrate has previously been shown to enable a cold sinter-assisted densification of PZT by a viscous phase sintering mechanism. In this paper, lead acetate trihydrate is demonstrated to lower the required temperature of the cold sintering step to 200°C. This densification process was described as a two-step process: cold sintering of PZT with lead acetate trihydrate and post-annealing the as-cold sintered PZT ceramics. Unlike in the case of lead nitrate, PZT densification with lead acetate trihydrate occurs by a liquid phase assisted sintering mechanism, leading to an as-cold sintered relative density of 84% at 200°C. After performing a post-anneal step at 900°C, >97% relative densities were achieved in samples that were cold sintered with lead acetate trihydrate. This step not only densified PZT but also refined the grain boundaries. In the post-annealed samples, the room-temperature relative permittivity at 100 Hz was ~1600, slightly higher than that reported in samples that used lead nitrate as a sintering aid; the loss tangent was about 3.8%. For measurements at 10 Hz, the remanent polarization in both cases was ~28 µC/cm². Both Rayleigh analysis and aging studies showed that a higher irreversible contribution to the permittivity exists in samples that used lead nitrate as a cold sintering aid.     

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.     

Effects of cerium doping on dielectric properties and defect mechanism of barium strontium titanate glass-ceramics

The effect of cerium content on phase evolution, dielectric properties and defect mechanism has been investigated in (Ba,Sr)TiO₃ glass-ceramics. Cerium mainly acts as an isovalent dopant in the B-site of ABO₃ perovskite structure at low content (1 mol%) and then cerium substitution gradually occurs in the A-site with increasing cerium content. A compensation mechanism related to variation in oxygen vacancy concentration has been identified. When cerium content increased to 2 mol%, the maximum values of dielectric constant and energy storage density were simultaneously achieved. The impedance spectra revealed the highest conductivity. It is due to the increase in the concentration of charge carriers accompanied by the decrease in the activation energy of oxygen vacancy migration. With a further addition of cerium to 3 mol%, the opposite trend was observed. The result is related to the presence of more cation vacancies, which, in turn, limits the diffusion rate of oxygen vacancy.     

Origin of low dielectric loss and giant dielectric response in (Nb+Al) co‐doped strontium titanate

(Nb+Al) co‐doped SrTiO₃ ceramics with a nominal composition of Sr(Nb_0.5Al_0.5)_xTi_1‐xO₃ (x = 0, 0.02, 0.04, and 0.06) were fabricated using the conventional solid‐state reaction method; giant permittivity (10500) and low dielectric loss (0.03) were obtained at x = 0.06. Dielectric and impedance spectroscopy, X‐ray photoelectron spectroscopy, and Raman spectroscopy, were employed to study why the dielectric property improved. The results indicate that the giant dielectric response occurs because of the combined effects of the off‐center Ti³⁺ reorientation and conduction of electrons with the polar ordering structure Ti³⁺/Ti⁴⁺. In contrast, the low dielectric loss can be attributed to electron localization that occurs because of the defect dipole . These fundamental understandings will benefit the design of doped SrTiO₃ ceramics with desired performance.     

钛酸锶钡压电陶瓷超细粉体的水热法合成

采用水热工艺制备不同组成的BaxSr1-xTiO3(BST)，利用FT-IR，XRD，TEM等技术分析了水热反应转变机理及相结构转变情况，同时对影响合成的工艺参数以及不同组成材料的居里温度变化进行了研究。结果表明：获得的BST粉体颗粒粒度较细，粒径为20～40nm。其最佳的工艺参数为n(Ba)／n(Ti)=3，n(Sr)／n(Ti)=1／4或者n(Ba)／n(Ti)=1／3，n(Sr)／n(Ti)=4／5，cKOH=1．5～2mol／L。制得不同组成粉体的居里温度呈规律性变化。     

High temperature dielectric properties of calcium zirconate

The electrical properties of dense, high purity CaZrO₃ discs, sintered at 1380°C with and without added ZrO₂, were investigated up to 950°C. Dielectric constant, loss tangent, and electrical conductivity were measured from 25 to 725°C, and the real and imaginary impedances were measured between 800 and 950°C by impedance spectroscopy techniques. Dielectric constant increased by 8% above 300°C and loss tangent increased from .1% at 25°C to ∼2% above 300°C. Activation energy of electrical conductivity determined between 300°C and 950°C by alternative current (AC) and direct current (DC) measurements. These results indicate that CaZrO₃ could be a useful dielectric material for capacitor applications up to 500°C. A reported decrease in conductivity due to addition of excess ZrO₂ into stoichiometric CaZrO₃ could not be confirmed.     

钛酸锶粉体合成新方法研究

以四氯化钛和氯化锶为原料，碳酸铵和氨水作沉淀剂化学共沉淀法合成钛酸锶粉体，研究了工艺条件对产品纯度和锶钛比的影响，最佳反应条件为：氯化锶与四氯化钛摩尔比为1．02，碳酸铵与氯化锶摩尔比为1．40，反应温度为室温，反应时间4h,pH=10，煅烧温度900℃，煅烧时间4h，所得产品经化学，红外光谱，电镜，X－射线衍射和原子发射光谱分析，分析结果显示：产品纯度高，粒径小，锶钛化合适。     

Dielectric relaxations of lead zirconate titanate films up to millimeter-wave frequencies

Modern high-frequency applications critically depend on the availability of data on the dielectric properties of functional materials in the microwave and millimeter-wave range. This paper investigates the dielectric response of polycrystalline lead zirconate titanate (PZT) thin films prepared by solution deposition at frequencies between 10 MHz and 70 GHz and temperatures of 305–395 K by measuring the S-parameters of coplanar waveguides (CPW). The real and imaginary parts of the permittivity of the PZT film are de-coupled from the electrical properties of both the fused silica substrate and the copper electrodes. Two dielectric relaxations are identified: one around 850 MHz, with room-temperature permittivity dropping from 1080 to 560, and one around 36 GHz, with permittivity dropping below 100, respectively. The low-frequency relaxation shows a shift to lower frequencies with increasing temperature; it is explained by the conventional Arlt model of mechanical shear mode resonance across the film thickness. The high-frequency relaxation, which is practically independent of temperature, is attributed to the response of ferroelectric domain walls.