Papers by Keyword: Barium Strontium Titanate

Abstract: Through the microwave-hydrothermal processing at 70 °C in 10 min, barium strontium titanate (BST) nanopowders are prepared by using butyl-titanate, barium nitrate and strontium nitrate as raw materials. Two kinds of dispersants namely polyethylene glycol 6000 and OP-10 are added, respectively. The dispersant mechanism and dosage on the crystal phase and microstructure are studied by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM). The results show that the dispersive effect of OP-10 is better than the polyethylene glycol 6000. The long chain of OP-10 can be used to disperse nanopowders through a space steric hindrance mechanism, well-dispersed BST nanopowders are obtained when mass percent ratio of dispersant (OP-10) is 5%.

Abstract: The ferroelectric ceramic, Barium Strontium Tinanate (Ba_0.7Sr_0.3TiO₃), was prepared by the sol-gel combustion method using citric acid, urea, and glycine as the fuel for reduce the calcination temperature. The molar ratio of sol powderto fuel was 1:1. All of the samples were calcined at 450, 550, 650, 750, 850 and 950°C for 2 h. Then,Ba_0.7Sr_0.3TiO₃ powders were applied with acid treatment process. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscope (TEM) analysis were used to characterize the crystal structure and microstructure. The perovskite phases of BST and the pyrochlore (BaCO₃,SrCO₃) were obtained after the calcinations temperature of 550°C. BST powders were applied with acid treatment process.The XRD result showed the pure perovskite phase without the phase of pyrochlore in all of the samples. Ba_0.7Sr_0.3TiO₃was in cubic structure, corresponding to JCPDS 34-0411. SEM analysis of BST powders calcined at 750°C.The particles were spherical morphology and had agglomerates while the particles sizes were larger corresponding with the increase of calcinations temperature.The results for TEM analysis of the BST powders prepared by using urea as the fuel had a smaller particles,and the average of particle size was about 47 nm.

Abstract: The influence of the BaSiO₃ dopant on the dielectric properties of (Ba,Sr)TiO₃(BST) capacitor ceramics was studied using conventional capacitor ceramics solid state method and XRD , SEM and other analytical methods. The results show that BaSiO₃ doping can improve the sintering and microstructure of the capacitor ceramics. SEM study show that BaSiO₃ doping can make grain grow uniformly and suppress the grain to grow up, and the structure of ceramics is compact with little pore. XRD study show that there is little SiO₂ phase and little influence of BST lattice parameter when BaSiO₃ doped amount is 3 mol%.The dielectric properties of BST ceramics doped with 3 mol% BaSiO₃ are as follows: dielectric constant (ε_r) of 1792, which is a little higher than undoped BST ceramics, tanδ of 1%, which is decreased 7.24% compared with undoped BST ceramics, and the sintering temperature decreases 40°C.

Abstract: Ba _1-x Sr_xTiO₃(x=0.6 to 0.9 interval of 0.1) ceramics were developed by a BT sol-assisted sintering technology with a mixed-phase sintering from the mixture of BT and ST powders synthetized by a solid-state reaction method. The sintering behavior and dielectric properties of the ceramics were investigated. Results show that the sintering activity of the ceramics becomes worse and worse when increased the strontium content, and the sintering condition have a remarkable effect on the density of the ceramics. Dense ceramics were obtained when sintered at 1280°C for 8h with a relatively density of above 94%. The composition had a strong effect on the dielectric properties, while the sintering schedule had a little influence on the dielectric temperature spectrum of the BST ceramics. The Ba _1-x Sr_xTiO₃(x=0.9) ceramic with dielectric constant～335, loss tangent～0.000625 at 1.85 GHz and 20°C, and good temperature stability of dielectric constant above the room temperature is attained.

Abstract: Barium strontium titanate nano powders were prepared by mixing ethanol solution of tetrabutyl titanate with an aqueous solution of Ba(OH)₂•8H₂O and Sr(OH)₂•8H₂O with a certain molar ratio of barium to strontium at 40°C－95°C. The products were characterized by thermogravimetry (TG), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), transmission electron microscope (TEM) and atomic force microscopy (AFM). The results show that the powders prepared with the reactant concentration of 0.8M are spherical in particle shape with the grain size of 50nm－65nm. When the annealing temperature of the powders is higher than 906°C, the hydroxyl groups existed in barium strontium titanate lattice are removed. XRD analysis demonstrate that the as-prepared powders are cubic phase. All the diffraction peaks are shifted towards higher diffraction angles and the lattice parameter a calculated decreases linearly with serial decrease of the molar ratio of barium to strontium.

Abstract: The growth of strontium doped barium titanate (BST) powder is performed by solid-state reaction. Microstructural characterization by SEM technique confirms the BST film is successfully formed on p-Si (100) substrate by spin coating technique. Dielectric properties of MFIS (Metal/ Ferroelectric/ Insulator/ Semiconductor) designs are measured by impedance analyzer (LCR meter, QuadTech :1730). P-E (polarization-electric field) hysteresis loops are also measured by applying the same triangular wave electric field in order to allow their application in NVFeRAM (Non-Volatile Ferroelectric Random Access Memory). The maximum remanent polarization density (P_r=38.6µC/cm²) is found at BST film 600°C. The film exhibits the potential to be a future promising memory. The results obtained from this research are quite interesting, acceptable, credible and applicable in use for NVFeRAM.

Abstract: Doping effect of Sb on Pb-free barium strontium titanate was investigated. The Sb doped (Ba,Sr)TiO3 ceramics were prepared by solid reactions in 1473-1623 K by employing 0~1.2 wt% Sb2O5 as main additives. Density changes with sintering temperature were determined. The morphology and microstructure of the Sb doping samples were analyzed by SEM. The dielectric properties such as permittivity and dielectric loss were measured. It was found that addition of Sb benefited to low temperature high density sintering process. When the addition amount of Sb2O5 was about 0.6 wt%, the dielectric loss of (Ba,Sr)TiO3 was decreased from 1.9% to about 0.4% while the dielectric constant was kept over 2000. Possible mechanism of the improvement by Sb addition was discussed too.

Abstract: Ba0.5Sr0.5TiO3:Pr powders co-doped with and without Al were synthesized by citrate-nitride combustion process. To investigate the effect and mechanism of Al dopant, samples with various Al3+ and Pr3+ content were prepared. The excitation and emission spectra were detected. Enhanced red emission around 613 nm was obtained by Al addition. Moreover, an emission at 491 nm was observed. Substitute situation of Pr3+ ions in the lattice was discussed. And the mechanism of energy transition was explained by the model of an intermediate charge transfer state.

Abstract: Ba0.9Sr0.1TiO3 ferroelectric ceramics with dopants of La₂O₃(0, 0.1, 0.1, 0.2 mol%) and Nb₂O₅(0, 0, 0.1, 0.1 mol%) were prepared in solid state process. The double donor substitutions can weaken lattice size effect by the two different size substitutions. XRD method was used to analyze the crystal structure of the samples, and SEM was used to observe the topography, grain’s size and ceramics density. The results of dielectric-frequency relation indicate that when the contents of La₂O₃ and Nb₂O₅ are both 0.10 mol%, the permittivity can reach to 150 000, and the dielectric loss keeps only 0.118. When the total donor content is lower than 0.40 mol%, compensation effect is dominated by electrons. The giant permittivity is attributed to electrons inside grain and insulated grain boundary. When the dopant content is higher than 0.40 mol%, the compensation effect is dominated by the host cation vacancies. The permittivity decreases rapidly with the increase of the donor concentration.

Abstract: _{Subscript text}Reactive ion etching of barium strontium titanate (BST) thin films using an SF₆/Ar plasma has been studied. BST surfaces before and after etching were analyzed by X-ray photoelectron spectroscopy to investigate the reaction ion etching mechanism, and chemical reactions had occurred between the F plasma and the Ba, Sr and Ti metal species. Fluorides of these metals were formed and some remained on the surface during the etching process. Ti can be removed completely by chemical reaction because the TiF₄ by-product is volatile. Minor quantities of Ti-F could still be detected by narrow scan X-ray photoelectron spectra, which was thought to be present in metal-oxy-fluoride(Metal-O-F). These species were investigated from O_1s spectra, and a fluoride-rich surface was formed during etching because the high boiling point BaF₂ and SrF₂ residues are hard to remove. The etching rate was limited to 14.28nm/min. A 1-minute Ar/10 plasma physical sputtering was carried out for every 4 minutes of surface etching, which effectively removed remaining surface residue. Sequential chemical reaction and sputtered etching is an effective etching method for BST films.