Low temperature fabrication of barium titanate hybrid films and their dielectric properties

A method for incorporating BT nano-crystalline into barium titanate (BT) films is proposed for a low temperature fabrication of high dielectric constant films. BT nanoparticles were synthesized by hydrolysis of a BT complex alkoxide in 2-methoxyethanol (ME)/ethanol cosolvent. As the ME volume fraction in the cosolvent (ME fraction) increased from 0 to 100%, the particle and crystal sizes tended to increase from 13.4 to 30.2 nm and from 15.8 to 31.4 nm, respectively, and the particle dispersion in the solution became more improved. The BT particles were mixed with BT complex alkoxide dissolved in an ME/ethanol cosolvent for preparing a precursor solution that was then spin-coated on a Pt substrate and dried at 150 °C. The dielectric constant of the spin-coated BT hybrid film increased with an increase in the volume fraction of the BT particles in the film. The dissipation factor of the hybrid film tended to decrease with an increase in the ME fraction in the precursor solution. The hybrid film fabricated at a BT fraction of 30% and an ME fraction of 25% attained a dielectric constant as high as 94.5 with a surface roughness of 14.0 nm and a dissipation factor of 0.11.     

Sandwich-type composite multilayer films of strontium titanate and barium strontium titanate and their controllable dielectric properties

It is a challenge to reduce the dielectric loss and increase the tunability of pure barium strontium titanate(BST)films for microwave tunable application because these two properties change simultaneously.Herein,a novel composite of strontium titanate(ST)and potassium-doped BST(KBST)has been designed as ST/KBST/ST sandwich-type film with various ST and KBST layers.X-ray diffraction patterns show that the film exhibits cubic perovskite polycrystalline structure composed of BST and ST phase,mainly grow along(110)crystal plane with average grain size of less than 20 nm and decreasing BST phase/ST phase ratio with increasing film thickness.Scanning electron microscope shows that no interfacial layer can be observed,indicating that ST and KBST are fully compounded.Low dielectric loss and high tunability at-10-10V and stable and excellent dielectric properties at 1 GHz are achieved,meeting the needs of microwave tunable application at high frequency.The surface structures are also studied by other analysis methods,and ST/MgBST/ST sandwich-type film is compared.     

高介电常数聚酰亚胺/钛酸钡复合膜的制备与性能研究

通过将聚酰胺酸溶液与硅烷偶联剂处理的钛酸钡(BaTiO3) 粒子进行溶液共混,亚胺化后得到高介电常数的聚酰亚胺/BaTiO3 复合膜。改性后的Ba TiO3 粒子可以均匀地分散在聚酰亚胺基体中, 制备过程中BaTiO3 粒子未发生经晶型改变,而聚酰亚胺分子链的堆积密度有所变化。复合膜的介电常数和介电损耗随着BaTiO3 粒子含量的增加而增加,在50%(体积分数)时,介电常数可达35,介电损耗为0.0082(10kHz),而且在相当大的温度和频率范围内保持稳定,是一种综合性能良好的高介电常数材料。     

Structural characteristics and dielectric properties of neodymium doped barium titanate

Neodymium (Nd) doped barium titanate powder (Ba_(1−x)Nd _x TiO₃) with x value varying from 0, 0.01, 0.03, 0.05, 0.07, 0.10 and 0.13 was prepared using the sol gel method. The powder samples were calcined at 700 °C and tetragonal phase appeared in the powders before they were sintered at 1250 °C for 3 h. The undoped samples have a polycrystalline tetragonal structure, but Nd doping into the BaTiO₃ caused phase transformation from tetragonal to cubic. The smaller grains (0.35 μm) produced with the addition of Nd is associated to the inhibition of grain growth of samples. The powders for each composition were pressed into pellets and tested as dielectric resonator antenna (DRA). It was found that on the actual antenna circuit, each sample showed a resonance frequency at X-band application and a dielectric constant value in the range of 51.25–56.89 and tangent loss was 0.039–0.045, depending on the concentration of the Nd at room temperature.     

钛酸锶钡(BST)薄膜的介电性能研究

采用射频磁控溅射法制备了BaxSr1-xTiO2（简称BST）薄膜材料,研究了不同膜厚,晶粒尺寸的BST薄膜的介电系数温度特性（ε1-T),频率特性（ε-r-f),电压特性（εr-U)及损耗的温度特性（tgδ-T),频率特性（tgδ-f),找出了BST薄膜的非线性,损耗随尺度变化的规律。     

Synthesis, characterization and dielectric properties of europium-doped barium titanate nanopowders

Europium-doped cubic barium titanate (BT) nanocrystals with % [Eu/Ti] mol ratio varying from 0.05 to 0.25 were prepared through hydrothermal route. The nano nature of these powders was confirmed by XRD and TEM studies. Pellets were prepared after calcining the powders at 1000 °C for 2 h. These pellets were annealed at 200, 500, 700 and 1000 °C for 2 h at each temperature and used for dielectric measurements. Raman spectra of two typical pellets with %[Eu/Ti] Eu/Ti mol ratios of 0.15 and 0.25 showed all the peaks characteristic of tetragonal BaTiO₃. Pure BT showed a low dielectric constant (DC) with a value of 398. Doping with small amounts of Eu resulted in many fold increase of DC values. A maximum value of 10576 at 1 KHz frequency was observed for the sample with % [Eu/Ti] mol ratio of 0.15. Lowering of Curie temperature T_c (95 to 110 °C) was observed for pure as well as Eu-doped barium titanate.     

Semiconducting properties of barium titanate and iron substituted barium titanate

Single crystals of barium titanate and members of the series BaTi_1?xFe_xO_3?xF_x have been grown from a potassium fluoride flux. These crystals were made conductive by heating in a sealed evacuated silica tube in the presence of freshly ground titanium. Electrical, optical and magnetic measurements were performed in order to characterize these crystals. Optical measurements indicated a decrease in the band edge from 3.2(1) eV for barium titanate to 2.8(1) eV for Bati_1?xFe_xO_3?xF_x(x = 0.02, 0.05, 0.07, 0.10). The photoelectrolytic behavior of reduced barium titanate was strongly quenched upon the substitution of iron and fluorine.     

改进的sol-gel工艺制备细晶Ba0.6Sr0.4TiO3陶瓷及其介电性能的研究

用改进的sol-gel工艺制备了细晶钛酸锶钡(Ba0.6Sr0.4TiO3,BST)陶瓷块体,研究了BST陶瓷的结晶与介电性能.在这种改进sol-gel的工艺中,用传统的固相反应煅烧形成BST粉体,经高能球磨制备BST纳米陶瓷粉体,再将一定质量的纳米粉体加入到相同化学组成的BST的溶胶液中,经普球球磨12h后,制备成悬浮性好,分散均匀的浆料.浆料可用来制备BST陶瓷,并在1200℃保温2h烧结成瓷,结果显示,BST陶瓷块体结构致密,晶粒尺寸在0.15～2μm之间.分析了样品的介电性能和晶粒尺寸对材料介电性能的影响.介电温谱显示,在0℃,100kHz时,相对介电常数为2500,介电损耗为0.02;并且存在明显的弥散相变.     

Ferroelectric and dielectric properties of sol-gel processed barium titanate ceramics and thin films

Ferroelectric and dielectric properties of barium titanate (BaTiO3) bulk ceramics and thin films have been investigated. The bulk ceramics and thin film samples have been prepared from barium acetate [Ba(CH3COO)2] and titanium(IV)isopropoxide [Ti(CH3)2CHO)4] precursors by sol-gel technique. The as-grown bulk powder and thin films were found to be amorphous, which crystallized to tetragonal phase after annealing at 700°C in air for one hour. The values of the spontaneous polarization (Ps), remanant polarization (Pr) and coercive field (Ec) of the bulk ceramics were found to be 19.0, 12.6 C cm–2 and 30 kVcm–1 respectively. In the case of the film, the values of Ps, Pr and Ec were respectively found to be 14.0, 3.2 Ccm–2 and 53 kVcm–1. The capacitance-voltage (C-V) characteristics of the film also showed polarization hysteresis. The values of the dielectric constant () of the bulk ceramic and thin film at 1 kHz were found to be 1235 and 370 respectively. Both the films and ceramics showed dielectric anomaly peaks at 125°C, showing ferroelectric to paraelectric phase transition.     

Preparation of powder barium titanate

Phase-pure BaTiO₃ powder (free of Ba₂TiO₄, BaCO₃, Ba(NO₃)₂, and OH impurities) with an average particle size of about 100 nm is prepared by solid-state reaction between titanium oxyhydroxide and barium hydroxide ground and mixed by sonication in an inert organic liquid.     

Influence of core-shell structured grain on dielectric properties of cerium-modified barium titanate

The dielectric properties and chemical inhomogenity of BaTiO₃ ceramics sintered with additions of CeO₂:1.5TiO₂ were investigated using TEM XRD and EDS. Grains had three regions: grain shell severely doped with cerium, grain core BaTiO₃ of greater purity, and a concentration gradient region where Curie temperatures were distributed. With decreasing temperatures, the volume fraction of ferroelectric domains in the concentration gradient region increased. Addition of CeO₂:1.5TiO₂ to BaTiO₃ decreased the tetragonality (c/a ratio) and the grain size, and lowered the Curie temperature by approximately 30 C per mol%. Even a small addition of 0.005 mol CeO₂:1.5TiO₂ to BaTiO₃ reduced the average grain size from 25 m to less than 1.25 m and grains of an average grain size were completely doped with cerium, which explained why the 130 C ferroelectric transition peak did not exist. The inhomogenity of the cerium concentration had a large influence on the dielectric temperature characteristic.     

Microstructure,dielectric properties and diffuse phase transition of barium stannate titanate ceramics

BaSn _x Ti_1–x O₃ (short for BTS) ceramics are prepared via the conventional solid state reaction method. The microstructures, diffuse phase transiton, dielectric and ferroelectric properties of BTS ceramics were investigated. These results indicate that Sn⁴⁺ ions have entered the unit cell maintaining the perovskite structure of solid solution. The incorporation of SnO₂ can limit grain growth in the BTS ceramics. The Curie temperature of BTS ceramics decreases with the increasing of tin content. Addition of tin can decrease dielectric loss of BTS ceramics at room temperature. The diffuseness of the phase transition of BTS ceramics enhances with the increasing of tin content. The coercive electric field (E _C) increases as tin content increases when x is 0.10–0.20. Moreover, the remanent polarization (P _r) of BTS ceramics decreases with the increasing of tin content.     

The effect of glass addition on the dielectric properties of barium strontium titanate

Ba_0.7Sr_0.3TiO₃ (BST) ceramics were prepared by the conventional solid state ceramic route. Different weight percentages of twelve different glasses were added to the calcined BST ceramics and sintered. The structure and microstructure of the sintered materials were investigated by X-ray diffraction and Scanning Electron Microscopic techniques. The low frequency dielectric properties of the glass-ceramic composites were measured using LCR meter. Some of the glasses improved the dielectric properties and considerably lowered the sintering temperature. The glasses were prepared and characterized under identical conditions. Among the different glasses, 1.5 wt% addition of 71ZnO–29B₂O₃ lowered the sintering temperature of BST to 975 °C with a dielectric loss of 9 × 10⁻³ and dielectric constant of 875 at 1 MHz. The curie temperature of BST ceramics was found to shift towards lower temperature with glass addition.     

Effect of phosphor doping on the microstructure and dielectric properties of barium titanate ceramics

The effect of phosphor doping on the sintering behaviour, microstructure and dielectric properties of BaTiO₃ has been investigated. Diisopropyl phosphinate is added to high-purity BaTiO₃ powder prepared by the wet chemical method with a final amount of 0.14 wt.% P₂O₅ with respect to the BaTiO₃. Phosphor-doped BaTiO₃ ceramics with a high density and uniform grain size have been produced by using wet processing and pressureless sintering without any binder. A scanning electron microscope, thermometric analysis, X-ray diffraction and an impedance analyser have been used to determine the microstructure as well as the dielectric properties. The phosphor cations can form a liquid phase belonging to the ternary system BaO-TiO₂-P₂O₅, leading to the formation of BaTiO₃ ceramics with high density at low temperature. Phosphor-doped BaTiO₃ ceramics with a high density of 96% D_th are obtained by sintering at 1200°C with a soaking time of 2 h. The dielectric constants of samples sintered at 1150 and 1200°C are as high as 6100 and 5500, respectively; the Curie temperature of samples decreases with decreasing sintering temperature. Doping with a small amount of phosphor can improve the sintering and dielectric properties of BaTiO₃ ceramics.     

Low dielectric loss and enhanced tunable properties of Cr-doped barium strontium titanate solid solution

The dielectric response and tunable properties of Cr-doped Ba_0.6Sr_0.4TiO₃ solid solution were investigated. The XRD patterns revealed that all of the doped specimens are cubic perovskite phase, and the SEM micrographs showed that the grain size increases with the increase of Cr content below 0.6 mol%. The dielectric frequency spectra of the doped BST solid solution showed that an additional relaxation of the doped specimens is observed at frequencies above 10 MHz. Both of the tunability and dissipation factor were improved by doping with Cr concentration lower than 1.0 mol% compared with undoped material. The 0.6 mol% Cr-doped specimen reveals a maximum tunability and figure of merit of 23.3% and 518.3, respectively. Extremely low dissipation factor in order of 5 × 10⁻⁴ is found for 0.4–0.6 mol% Cr-doped BST solid solution. The dramatically low dissipation factor of the specimen is explained by the reducing of Cr³⁺ to Cr²⁺ and the acceptor action of Cr³⁺ and Cr²⁺ which neutralized the donor action of oxygen vacancies.     

Preparation of barium titanate nanocube particles by solvothermal method and their characterization

Barium titanate (BaTiO₃) nanocube particles below 20 nm were prepared by solvothermal method. A selection of organic solvent and inorganic materials of Ba and Ti sources was most important for the preparation of nanocubes. A nucleation and particle growth of BaTiO₃ nanoparticles led to a formation of the BaTiO₃ nanocubes with a size of 10–15 nm at temperatures above 200 °C.     

Electrical and dielectric properties of polypropylene nanocomposites based on carbon nanotubes and barium titanate nanoparticles

Functional polypropylene (PP) nanocomposites were prepared by melt compounding with multiwalled carbon nanotubes (MWNT) as the electrically conductive component and barium titanate (BT) spherical nanoparticles as the ferroelectric component. To make PP electrically conductive, more than 3 wt.% MWNT is required. Surface modification of either MWNT or BT with titanate coupling agent further improves the electrical conductivity of the PP/MWNT/BT ternary nanocomposites. Interestingly, by modifying both MWNT and BT, 2 wt.% MWNT are sufficient to make the ternary nanocomposite electrically conductive. In addition, the incorporation of MWNT greatly increases the dielectric permittivity of PP/BT nanocomposites. However, to retain a low dielectric loss, the MWNT loading should be slightly less than the percolation threshold of the nanocomposites. The improved electrical conductivity and dielectric properties make the ternary nanocomposites attractive in practical applications.     

Synthesis and properties of manganese-doped barium titanate

An oxalate route for the production of BaTiO₃ has been modified to incorporate Mn (upto 2%) as a dopant and the reaction sequence has been studied. The resulting Mn-doped BaTiO₃ exhibits a dielectric constant with an increasing insensitivity to temperature and applied a.c. field as the Mn content is increased. These samples possess a high electrical resistivity even after treatment in hydrogen at 1100°C and are therefore suitable as dielectric for multilayer capacitors with base metal electrodes.     

Influence of microstructure on dielectric properties of Nd-doped barium titanate synthesized by hydrothermal method

Nd-doped barium titanates were successfully synthesized via a hydrothermal route. The as-prepared barium titanate was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transformation infrared spectroscopy (FTIR), and Vis–NIR spectroscopy respectively. The results show that pure and Nd-doped barium titanate powders have cubic perovskite structure. After sintering at a temperature of 1,250 °C for 2 h, the phase compositions of all barium titanate are tetragonal phase structure. Vis–NIR spectra well confirmed that Nd³⁺ have been doped into barium titanate. The particle diameters of Nd-doped barium titanate powders and ceramics become samller with the increase of Nd³⁺ content. When Nd/Ba molar ratio is 0.02, the dielectric loss (0.0008) of the powder measured at 1 MHz and room temperature dramatically decreases by 99 % comparing with pure barium titanate (0.083) and shows frequency independence with the frequency increasing from 40 Hz to 1 MHz. The dielectric constant and dielectric loss are 436 and 0.09 after sintering. The Nd-doped BaTiO₃ show an improvement in the dielectric quality which possess a decreased sensitivity to frequency for both the dielectric constant and dielectric loss. Such improvements are of potential importance for high energy density and low loss.