Papers by Keyword: Barium Strontium Titanate

Abstract: The dielectric properties of Sb₂O₃-doped (Ba_0.732Sr_0.26Nd_0.008)TiO_3.004 ceramics fabricated by conventional solid state method were investigated. The structure was identified by X-ray diffraction method and scanning electron microscope was also employed to observe the surface morphologies. It is confirmed that Sb₂O₃-doped (Ba_0.732Sr_0.26Nd_0.008)TiO_3.004 ceramics exhibit perovskite structure and with increasing Sb₂O₃ content Ba₆Ti₁₇O₄₀ (space group C2/c (15) ) forms as a secondary phase. The experimental results reveal that the addition of Sb₂O₃ into (Ba_0.732Sr_0.26Nd_0.008)TiO_3.004 ceramics reduce the dielectric constant and Curie temperature due to the substitution for A/B-sites with Sb³⁺ ions. The standing voltage increases with increasing Sb₂O₃ content while the dielectric loss and resistivity initially decrease and then increase with the increase of Sb₂O₃ concentration. The temperature dependence of dielectric properties at different frequencies was studied as well. It indicates that the tetragonal-cubic phase transition peak is suppressed as the Sb₂O₃ content increases and the peak value reduces with the increase of frequency.

Abstract: The electrical and dielectric properties of Ba0.3Sr0.7TiO₃ (BST), as a function of annealed temperature and oxygen partial pressure (P(O₂)) , were studied in this paper. The resistivity data were fit to a p type model involving only doubly ionized oxygen vacancies, holes, and accidental acceptor impurities, and it decreased as P(O₂) and temperature increased. The breakdown strength exhibited the same trend with resistivity. The breakdown strength exhibited the same trend with resistivity. The maximum dielectric constant of BST was observed under the lowest P(O₂) at the temperature of 900°C. BST annealed under P(O₂) of 0.1 atm at the temperature of 800°C obtained the highest volume energy storage density.

Abstract: The synthesis of Ba_1-xSr_xTiO₃ (BST) powders was attempted using KOH-KNO3 molten salt. The starting materials, Ba(NO3)2, Sr(NO3)2 ,TiO2,and the mixed salt of KOH-KNO3, were well-mixed. The mixture was heated at 300 to 500°C for 1 hour, and the product was thoroughly washed with de- ionized hot water. When the mixture containing excess TiO2 was used, single-phase BST powders with a particle size of 10~50nm were obtained.

Abstract: Barium-strontium titanate Ba_1-xSr_xTiO₃ [0≤x≤1] has been investigated for tunable microwave application due to their high permittivity, low losses and high tunability. The influence of MgF₂ additives on the dielectric performance of Ba_0.6Sr_0.4TiO₃ (BSTO) were investigated in this paper. MgF₂ doped BSTO ceramics were prepared using the conventional mixed oxide techniques. The phase structure, microstructure and dielectric properties of MgF₂ doped BSTO ceramics were studied. The XRD patterns showed that all the samples exhibit a perovskite phase. A secondary phase of MgO was observed with excessive MgF₂ additives. The grain size of MgF₂ doped BSTO ceramics was slightly increased with the increasing of MgF₂ additives, while the distributed porosity was concentrated to get larger. The relative permittivity, dielectric loss and tunability were decreased accordingly. The relative permittivity was reduced from 3717 (pure Ba_0.6Sr_0.4TiO₃) to 680 (6 wt % MgF₂ doped BSTO), while the tunability changed from 51.7 % to 6.5 %. The dielectric losses were decreased from 0.004 to less than 0.001. The Curie temperature of MgF₂ doped BSTO was first decreased with the additives of MgF₂ (x<2 wt %) then remain the same with the rise of MgF₂ (2≤x≤6) content.

Abstract: The structural and dielectric properties of Si-B-O doped Ba_0.60Sr_0.40TiO₃ (BST) glass-ceramics prepared by using sol-gel derived powders have been investigated. The secondary phase of BaTi₂Si₂O₈ is clearly observable in BST glass-ceramics when the concentration of Si-B-O is equal to or more than 20mol%. The samples with high Si-B-O doping levels can be sintered into dense microstructure in low sintering temperature (below 1000°C). The dielectric peaks of BST glass-ceramics are markedly suppressed, broadened and shifted to low temperature with increasing the concentration of Si-B-O, accompanying an increased diffuseness of the dielectric peak due to the ionic substitution, which follows well the Lorenz-type relation.

Abstract: The Ba_0.6Sr_0.4TiO3 (BSTO) ceramics were prepared by a traditional electrical ceramic method. Effects of co-doping low dielectric constant oxides Al₂O₃ and MgO on microstructure and dielectric properties of Ba_0.6Sr_0.4TiO₃ ceramics were investigated. The results show that BSTO/MgO/Al₂O₃ (BMA) ceramics can be sintered at 1300°C. The main crystal phases are cubic perovskite structure Ba_0.6Sr_0.4TiO₃ and face-centered-cubic spinel structure MgAl₂O₄. Al³⁺ is easier to enter Ba_0.6Sr_0.4TiO₃ lattice in the replacement of Ti⁴⁺ than Mg²⁺. When Al₂O₃ content exceeds 20wt%, Al₂O₃ would react with BaAl₂O₄ to generate a new phase of BaAl₁₂O₁₉. Proper amount of Al₂O₃-MgO can reduce the dielectric constant of BSTO ceramics and result in the higher tunability. There is obvious frequency dispersion characteristic in BMA ceramics and the curie temperature of ceramics decreases with the increase of Al₂O₃. The BMA ceramics with 20 wt% Al₂O₃ exhibit good dielectric properties, with ε_r of 1314, tanδ of 0.003 at 10 kHz, and the dielectric constant tunability of 35.2% under a dc electric field of 1.0 kV/mm, which are useful for potential tunable device applications.

Abstract: It is important to develop a new special material to meet the requirement of advanced industry. The BST (Ba_0.8Sr_0.2TiO₃) ceramics doped La₂O₃ and Sm₂O₃ was fabricated by the conventional method, and was tested by X-ray diffraction (XRD), Complex Impedance Testing Instrument, LCR Tester with temperature controlling systems. The results indicate that dielectric property of BST-based ceramics doped 0.05 mol% La₂O₃ and 0.2 mol% Sm₂O₃ simultaneously is the best, and Sm₂O₃ had applications of removing T_c of matrix material to a low temperature and making peak wider. The calcining temperature of samples was 1280 °C.

Abstract: Barium strontium titanate (Ba_0.6Sr_0.4TiO₃: BST) powders were prepared by the oxalate co-precipitation method. The ceramics from thus obtained BST powders with B₂O₃-Li₂CO₃ addition were prepared by conventional oxide mixing method. The powders and the ceramics were observed and analyzed by SEM and X-ray diffraction. The effects of B₂O₃-Li₂CO₃ addition and powder properties on the sintering behavior and the dielectric properties of BST-based ceramics were investigated. SEM results revealed that the BST powders are micron-sized with cauliflower-shaped rough surface leading the specific surface area reaches 18.52m²/g. In dilatometric studies, the ceramics without B₂O₃-Li₂CO₃ addition didn’t produce the desired shrinkage and dense microstructure at relative low temperatures (<1000°C). However, the sintering temperature is decreased to 850°C by addition of small amount (≤3wt %) of B₂O₃ and Li₂CO₃. This was also verified in sintered microstructures. The XRD results showed that the main phase of the ceramics was BST without any other crystalline phases of remarkable extent. With increasing of B₂O₃-Li₂CO₃ content, the permittivity and the tunability of the ceramics were decreased.

Abstract: BaxSr1-xTiO3 (BST) thin films were deposited by modified CSD, in which partially hydrolyzed Ti-alkoxide was reacted with Ba-Sr precursor solution to form highly polymerized BST precursor solutions, leading to the better electrical properties of the resultant thin films. BST precursor solutions of 0.1 M were prepared to deposit BST thin layers of 17nm ~ 20nm for one dip-coating operation with different barium to strontium ratio of Ba/Sr = 90/10, 70/30 and 50/50. Modified CSD-derived BST thin films were deposited on a Si wafer with Pt electrode or CSD-derived LaNiO3 (LNO) seeding layer with preferred orientation. BST thin films exhibited ferroelectric or paraelectric properties, depending upon the Ba/Sr ratio. Better electrical properties for the BST thin films were observed on a LNO seeding layer. Maximum tunability of our BST film was 41 % at 1MHz.

Abstract: BaxSr1-xTiO3 (0.2≤x≤0.5) ceramics with 10 vol% BaO-SiO2-B2O3 glass addition were prepared. The microstructure and dielectric properties were investigated by XRD, SEM, ferroelectric tester and impedance analyzer. The results show that with the decrease of x, the pulse breakdown strength of the samples is increased, and the dielectric constant and dielectric loss is decreased gradually. In the frequency from 10 kHz to 20 MHz, the dielectric constant of all the samples show good frequency stability. For x=0.2, the samples exhibit high breakdown strength of 37.7 kV/mm, moderate dielectric constant of 311 and low dielectric loss of 5×10-4,which is a promising dielectric for pulsed power applications.