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1.
An addition of just 0.4 wt% Li2O to (Ba0.6Sr0.4)TiO3 powder was able to reduce the sintering temperature to ≤900°C and produce ceramics with a relative density of 97%. Small amounts of two secondary phases were formed during this process: Li2TiO3 and Ba2TiO4. The addition of Li2O depresses the ferroelectric character of the (Ba0.6Sr0.4)TiO3 and, as a result, reduces the permittivity, improves the temperature coefficient of permittivity, and reduces the dielectric losses. The tunability shows no significant variation with Li2O concentration and remains between 16.5% and 13.5%. A low-temperature sintering mechanism was proposed. The mechanism involves the intermediate formation of BaCO3, its melting and the incorporation of Li+ into the BST. The sintering mechanism can be characterized as reactive liquid-phase sintering.  相似文献   

2.
Barium strontium titanate is a promising material for microwave-phased array applications. 1,2 In this study, highly dense and fine-grained Ba0.6Sr0.4TiO3 ceramics were prepared using the spark plasma sintering (SPS) technique. The structure and dielectric tunable properties of the samples were investigated. The "distorted nano-region" emerged in the interior of the grains of SPS samples, and resulted in the deterioration of the dielectric tunable properties of Ba x Sr1− x TiO3. This phenomenon indirectly testified to the assumption of the "polar nano-region" mechanism. After the SPS samples were annealed, the "distorted nano-region" disappeared and better dielectric tunable properties were obtained. The dielectric constant was decreased to 1048, and the K value (Commutation Quality Factor) reached 7089.  相似文献   

3.
Herein we report on a simple, low cost, and feasible route for the construction of PbZr0.4Ti0.6O3 (PZT)- or Ba0.9Sr0.1TiO3 (BST)-based optical microcavities using a single chemical solution containing polymer polyvinylpyrrolidone. The obtained multilayer systems not only exhibit good ferroelectric performance, but also display well-defined resonant modes with a quality factor of no <66. Compared with PZT microcavities, the optical properties of the BST microcavities appear to be superior.  相似文献   

4.
0.60Ba0.6Sr0.4TiO3(BST)–(0.40− x )Mg2SiO4(MS)– x Al2O3 ( x =0, 0.5, 3, 5wt%) composite ceramics exhibit excellent characteristics suitable for tunable device applications. With increasing amount of Al, the dielectric peak can be quantitatively broadened and suppressed; the "phase transition temperature" T c or ( T m) shifts to a lower temperature. Meanwhile, the tunability is still high in a wider temperature range. Far from T c, pyroelectric effects are observed by using the Byer and Roundy technology and Slim polarization hysteresis loops are observed under high ac dielectric field at 10Hz. These proved the existence of spontaneous polarization in certain possible orientations in a broad temperature range above T c in the paraelectric medium and reveal why 0.60BST–(0.40− x )MS– x Al2O3 have such remarkable dielectric nonlinearity.  相似文献   

5.
A sol-gel process was used to prepare pyroelectric Ba0.8Sr0.2TiO3 thin films with large columnar grains (100–200 nm in diameter) on Pt/Ti/SiO2/Si substrates, via using a 0.05 M solution precursor. The relationship between dielectric constant and temperature (ɛr- T ) showed two distinctive phase transitions in the Ba0.8Sr0.2TiO3 thin films. Both the remnant polarization and the coercive field decreased as the temperature increased from −73°C to 40°C. Its low dissipation factor (tan δ= 2.6%) and high pyroelectric coefficient ( p = 4.6 × 10−4 C·(m2·K)−1 at 33°C), together with its good insulating properties, made the prepared Ba0.8Sr0.2TiO3 thin films promising for use in uncooled infrared detectors and thermal imaging applications.  相似文献   

6.
The effects of heating rate on the sintering behavior and the dielectric properties of Ba0.7Sr0.3TiO3 ceramics prepared by boron-containing liquid-phase sintering were investigated. When 0.5 wt% B2O3 was added to Ba0.7Sr0.3TiO3, sintering was achieved at ∼1150°C, and the overdoped B2O3 did not form an adequate amount of liquid phase or volatilize; it remained in the samples and formed a secondary phase. A transition broadening was observed as the heating rate increased. As the heating rate increased, the Curie temperature increased and the maximum dielectric constant ( k max) at the Curie temperature decreased. This result is attributable to a decrease in the diffuseness parameter (δ) and the tetragonality ( c / a ).  相似文献   

7.
We have investigated the effects of donor, acceptor, and donor–acceptor codoping on both the dielectric properties and the leakage current behavior of Ba0.6Sr0.4TiO3 thin films prepared by the metalorganic solution deposition technique. La and Co were selected as donor and acceptor dopants, respectively. The electrical properties depend strongly on the type of dopants. Compared with others, codoped BST films have a much lower loss tangent, higher figure of merit, and lower leakage current. The electronic conduction mechanisms of the three types of dopants are reported.  相似文献   

8.
Crack-free Ba0.9Sr0.1TiO3 (BST) and Mn-doped Ba0.9Sr0.1TiO3 (BSTM) multilayers with thickness over 2 μm have been prepared by chemical solution deposition based on one single precursor. Both multilayers exhibit good performance as Bragg reflectors. Mn doping tends to suppress the leakage current in BST multilayers effectively by smoothing the layers and the reduction of the charge carries. The Mn-doped BST multilayer displays an excellent ferroelectric property, with an average remnant polarization ( P r+– P r)/2 of 12.69 μC/cm2 and an average coercive field ( E + – E )/2 of about 72.95 kV/cm under an applied field of 440 kV/cm.  相似文献   

9.
The dielectric properties of (Ba0.6Sr0.4)TiO3 and Al2O3-doped (Ba0.6Sr0.4)TiO3 have been characterized. The grain size of the specimen is maximum for (Ba0.6Sr0.4)TiO3 that has been doped with 1 wt% Al2O3. The density and the real part of the relative dielectric constant each decrease as the Al2O3 content increases. The loss factor is minimum for (Ba0.6Sr0.4)TiO3 that has been doped with 2 wt% Al2O3. The dielectric constant of the specimens decreases as the applied dc field increases. The influence of the dc field on the loss factor is much less than that on the dielectric constant. The tunability is ∼24% for (Ba0.6Sr0.4)TiO3 that has been doped with 1 wt% Al2O3.  相似文献   

10.
The effects of B2O3 addition on the sintering behavior and the dielectric and ferroelectric properties of Ba0.7Sr0.3TiO3 (BST) ceramics were investigated. The dielectric and ferroelectric properties of a BST sample with 0.5 wt% B2O3 sintered at <1150°C were as good as those of undoped BST sintered at 1350°C, and the dielectric loss was better. When >1.0 wt% B2O3 was added to BST, the overdoped B2O3 did not form a liquid phase or volatilize; it remained in the samples and formed a secondary phase that lowered the sintering behavior and the dielectric and ferroelectric properties of the BST.  相似文献   

11.
The formation of BaTiO3 from equimolar BaCO3 and TiO2 (rutile) mixtures was studied in air and in CO2. A small amount of BaTiO3 is formed first directly from BaCO3 and TiO2 at the surface of contact. From then on it is a diffusion-controlled reaction, and both BaTiO3 and Ba2TiO4 are produced, with Ba2TiO4 being formed in much larger amounts. In 1 atmosphere of CO2, the intermediate Ba2TiO4 was suppressed up to a temperature of about 1100°C. in agreement with thermodynamic calculations. Ba2TiO4 reacts fast with 1 atmosphere of CO2 below about 1100°C. to produce BaTiO3and BaCO3  相似文献   

12.
The effects of microstructure on the optical properties of La0.4Sr0.6TiO3 thin films were investigated. Dense films with the thickness of ∼200 nm and grain size 14–30 nm were produced on monocrystalline sapphire substrates by using a polymeric precursor spin coating technique at annealing temperatures under 800°C. X-ray data showed the formation of a single-phase cubic perovskite-type structure similar to undoped SrTiO3 for annealing temperatures >500°C. The results of optical measurements showed that the optical spectra varied with the change of the grain size. From these data, the absorption coefficients were calculated and the band gap energy determined. In agreement with the quantum confinement model, it was shown that the band gap energy increased as the grain size decreased.  相似文献   

13.
(Ba0.6Sr0.4) TiO3 thick films doped with glass slurry were fabricated by the screen-printing technique. The dielectric properties and the sintering mechanism were investigated. The films can be sintered at 600°C. The dielectric constant is 88 and the dielectric loss is 0.002 with a tunability of 23.86% under 100 kV/cm. Higher dielectric constant and tunability were obtained in the samples sintered at higher temperatures. The highest tunability is 61.12% under 150 kV/cm in the sample sintered at 800°C. The low sintering temperature and dielectric loss of the glass-doped thick films make them potential candidates for LTCC and microwave tunable devices.  相似文献   

14.
Ba1– x Pb x TiO3 powder with a fixed composition was prepared by the reaction of BaTiO3 powders with molten PbCl2at various PbCl2/BaTiO3 molar ratios at 600° and 800°C in a nitrogen atmosphere. When 0.1 μm powder was used, the reaction was finished when x = 0.9. Two phases of BaTiO3and a solid solution of Ba1– x Pb x TiO3 coexisted, but the final phase gave a solid solution of Ba1– x Pb x TiO3 at 800°C. When 0.5 μm powder was used, the two phases coexisted in the products at 600°C at PbCl2/BaTiO3= 1.0. A sintered compact of Ba1– x Pb x TiO3 powders solid solution was prepared by hot isostatic pressing, and its dielectric constant was measured in the temperature range 20°–550°C.  相似文献   

15.
Pb0.6Sr0.4TiO3 (PST) ferroelectric thin films were prepared on two different substrates by sol–gel methods. Films derived on the LaNiO(LNO)/Pt/Ti/SiO2/Si substrates showed a strong (100) preferred orientation. The PST thin films grown on the LNO/Pt/Ti/SiO2/Si(100) substrate showed a non-uniform rounded grain size distribution and have a larger polarization and lower coercive field E c. The dependence of electrical properties derived on the Pt/Ti/SiO2/Si and LNO/Pt/Ti/SiO2/Si substrates has been studied, with a focus on the change of dielectric constant versus direct current (DC) bias field. The dielectric and ferroelectric properties of the Pb0.6Sr0.4TiO3 thin films deposition on two kinds of substrates were investigated as a function of temperature, frequency and DC bias field.  相似文献   

16.
Metallic and transparent La0.5Sr0.5TiO3+ x /2 films were prepared by the chemical solution deposition (CSD) method using topotactic reduction processing. The use of Si powder as the reducing agent was facile and allowed easy manipulation. It was observed that metallic (resistivity at 300 K ∼2.43 mΩ cm) and transparent (∼80% transmittance at visible light) La0.5Sr0.5TiO3+ x /2 films could be obtained with an annealing temperature of 900°C, which was significantly lower than the hydrogen reduction temperature (∼1400°C). The successful preparation of metallic and transparent La0.5Sr0.5TiO3+ x /2 films using CSD has provided a feasible route for depositing other perovskite-structured functional layers on La0.5Sr0.5TiO3+ x /2 films using this low-cost all CSD method.  相似文献   

17.
Nano-powders of BaTiO3, SrTiO3, Ba0.6Sr0.4TiO3 (BST64), and a mixture of the composition (BaTiO3)0.6(SrTiO3)04 with particle sizes in the range of 60–80 nm were consolidated by spark plasma sintering (SPS). An experimental procedure is outlined that allows the determination of a "kinetic window," defined as the temperature interval within which the densification process can be kinetically separated from the grain growth one, enabling preparation of dense nanostructured ceramics. The width of this window varied from almost zero for BST64 to 125°C for the (BaTiO3)0.6(SrTiO3)0.4 mixture. During the densification (sintering) of the (BaTiO3)0.6(SrTiO3)04 mixture, BST64 is formed. The main part of this reaction occurs in a fully densified body through which suggesting that the constitutional phase(s) have a self-pinning effect on the grain growth.  相似文献   

18.
Microwave Dielectric Properties of A6B5O18-Type Perovskites   总被引:1,自引:1,他引:0  
Cation-deficient perovskites with the general formula A6B5O18 (A=Ba, Sr, La; B=Nb, Ta, Ti, Zr, Mg, and Zn) have been synthesized and their microwave dielectric properties have been investigated. X-ray diffraction studies indicate the formation of monophase materials. The structures of Ba6Ta4TiO18 and Ba5SrTa4TiO18 are different from that of Sr6Ta4TiO18. The A6B5O18 have Q × f in the range 5600–51 000 GHz, dielectric constants 26–48, and the temperature coefficient of resonant frequency varies from −39 to +83 ppm/°C, depending on the composition. Scanning electron microscopy studies show that the grain size decreases with an increase in the Sr content.  相似文献   

19.
Ba0.55Sr0.45TiO3/MgO composites were successfully prepared by the heterogeneous precipitation method and their structural, surface morphological, tunable properties, and dielectric properties at microwave frequency were systemically investigated. Compared with the sample prepared by the traditional solid-state method, the sample prepared by the heterogeneous precipitation method exhibits a smaller grain size, more uniform microstructure, higher tunability, and lower microwave loss, and these properties are very beneficial to the development of the microwave tunable devices application. Moreover, the effects of La2O3 doping on the dielectric and tunable properties of BST/MgO composites are investigated. The result shows that the La3+-doped sample has higher tunability and lower microwave loss than the undoped one.  相似文献   

20.
This study investigates the effect of CuO on the sintering behavior, dielectric properties, and microstructures of Ba0.6Sr0.4TiO3 (BST) ceramics. The ceramics were sintered in air at temperatures ranging from 1000° to 1230°C. It is found that a small amount of added CuO (0.6 mol%) can significantly increase the density and improve the dielectric properties of BST ceramics. Doped BST ceramics can be sintered to a density >95% of the theoretical density at 1150°C. scanning electron microscopic observations show that the BST grain sizes increase with increasing amounts of CuO. No secondary phases in the BST ceramics are observed using X-ray diffraction pattern for CuO additions up to 0.9 mol%. However, compositional analysis using transmission electron microscopy-EDX for the BST ceramics with 0.9 mol% CuO sintered at 1150°C showed that a small level of secondary phase formation is present. On the other hand, large dislocations are observed for BST with 0.6 mol% CuO addition as a result of lattice distortion, which creates the vacancy condensation because of the atomic mismatch in the solid solutions. Optimal CuO doping concentrations can reduce the loss tangents of BST that can also ensure a high dielectric constant. When the doping concentration of CuO is 0.6 mol% and the ceramic is sintered at 1150°C, the BST ceramic has the following properties at 1 MHz: dielectric constant=4094, tan δ=0.55%.  相似文献   

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