Microwave dielectric and elastic properties of glass-added Ba6−3xR8+2xTi18O54 (x = 2/3)

Microwave dielectric properties of Ba_6−3xSm_8+2xTi₁₈O₅₄ (x = 2/3) [BST] ceramics with the addition of 0–3 wt.% of various glasses have been studied. It has been found that the addition of 0.5 wt.% of the glasses decreases the sintering temperature by about 150 °C. In general, addition of 0.5 wt.% of Zn, Mg and Pb-based glasses deteriorate the quality factor, whereas aluminum and barium borosilicates do not decrease it considerably. The quality factor and dielectric constant decrease with increasing amount of glass. The temperature coefficient of resonant frequency shifts towards positive or negative depending on the composition of the glass. A glass–ceramic composite with a dielectric constant 64, Q × f nearly 8500 GHz and near to zero τ_f could be obtained at a sintering temperature of 1175 °C when 3–4 wt.% Al₂O₃–B₂O₃–SiO₂ glass was added to BST ceramic. The Young's modulus decreases with increasing amount of glass, irrespective of the composition of glass.     

Mg掺杂对 Ba0.6Sr0.4TiO3薄膜介电性能的影响

应用Sol-Gel工艺制备了组份为(1-y)Ba 0.6Sr0.4TiO3-yMgO的薄膜材料,研究了Mg掺杂BST薄膜晶相结构、介电性能以及绝缘性能的影响规律.实验发现随着Mg掺杂量的增加,BST薄膜的介电常数、损耗因子以及电容变化率减小,其电阻率则增加;当Mg掺杂量分数为5%时,其介电常数为380,损耗因子为0.013,电容变化率为17.5%,电阻率为1.0×1012Ω@crm.     

Using a Two‐Level Structure to Manage the Point Location Problem in Explicit Model Predictive Control

The problem of determining the state region in which the current state point lies is referred to as the point location problem in the explicit model predictive control. In this paper, a two‐level structure to store the state regions is proposed and two efficient methods for solving the point‐location problem are developed; these are the two‐level grid (TLG) method and the grid‐BST method. The TLG method uses a tow‐level hash table. Before building the two‐level structure, the synonymy partitions are merged to reduce the memory storage demand. By setting each parameter in a triplet, the two‐level hash table can reach its optimal state and balance the complexity among the memory storage, reprocessing (offline computation) and the online computation. The grid‐BST method uses hash table as the first‐level structure and builds the binary search tree in the hash grid in which there are many partitions. This two‐level structure reduces reprocessing time significantly especially when the state partitions and the piecewise affine control laws (PWA control laws) are in a large number. Using the hyperplane (HP) as the node (not leaf node) of the tree, the method only stores all the different PWA control laws instead of the state partitions. The two proposed methods overcome the quick complexity growth when the number of polyhedral partitions increases and 2 numerical examples show the advantages of the proposed two methods.     

Mn掺杂对BST／SBN复相陶瓷相组成和结构的影响

利用传统氧化物烧结方法制备了掺杂Mn的BST／SBN复相陶瓷，采用X射线衍射仪和扫描电子显微镜详细研究了Mn掺杂对复相陶瓷的相组成和微观结构的影响。结果表明，掺杂Mn对钙钛矿和钨青铜两相共存没有影响：Mn以Mn^3＋的形态在两相中固溶，与钙钛矿相形成间隙固溶体，而与钨青铜相形成置换固溶体：随着Mn掺量增加，钙钛矿相的相对含量逐渐增高，而钨青铜相的含量则降低：掺杂适量的Mn有利于抑制钨青铜相的晶粒异常长大并提高复相陶瓷的致密度。     

Electrical characteristics of aluminum-zirconium oxide-barium magnesium fluoride-p silicon MIS capacitors

The Barium Magnesium Fluoride films have been deposited on p-Si wafers at a temperature in the range of 400-450°C in an ion assisted deposition system. X-ray diffraction analysis shows that the films are polycrystalline in nature. The BMF films were encapsulated with an electron beam evaporated Zro2 film of thickness 300°A. The capacitance-voltage (C-V) charactersitics of Aluminum-ZrO2-BMF-p Si MIS capacitors show hysteresis and the direction of the hysterisis correponds to ferroelectric polarization in the BMF film. The shift in threshold voltage was found to depend on bias voltage, ramp rate as well as measurement temperature.     

Effect of uniform and periodic doping by Ce on the properties of barium strontium titanate thin films

A significant decrease in the dielectric loss and leakage current by introducing Ce in small amounts into BST thin films is demonstrated. The other effects of Ce doping are a lowering of the dielectric constant and a lower temperature coefficient of dielectric constant. In films containing a periodic fluctuation of Ce concentration through the thickness, prepared using a multilayer approach, the dielectric loss is further reduced. The periodicity of the composition is shown to have a significant effect on the properties. The properties of the multilayer films are seen to be significantly different from the single layer films of corresponding average composition.     

氧退火对SiO2/Si衬底BST薄膜特性的影响

利用氩离子束镀膜技术和硅平面工艺在经过干氧氧化的硅衬底上制备一层钛酸锶钡薄膜 ,并在氧气中进行不同条件的退火处理 ,然后蒸铝及利用光刻技术制作铝电极而形成 MIOS电容结构 ,研究其物理及电学特性。结果表明 ,氧退火条件对衬底的钛酸锶钡薄膜的物理及电学特性有较为明显的影响。     

改进sol-gel技术BST薄膜的制备及性能研究

为了制备高性能BST薄膜,采用改进的溶胶 凝胶(sol gel)方法在Pt/Ti/SiO2/Si基片上制备出了不同结构、不同组成的BST薄膜;研究了BST薄膜的微观结构及其介电、铁电性能。XRD分析表明,当热处理温度为750℃时,得到完整钙钛矿结构的薄膜材料。SEM电镜显示,含种子层的Ⅱ、Ⅲ、Ⅳ3种不同类型的BST薄膜的结晶状况有很大改善。得到的BST20薄膜的介电峰温区覆盖常温段,介电常数为405,介电损耗为0.011,剩余极化强度为Pr=2.3μC·cm-2,矫顽场为Ec=45kV/cm。     

新型sol-gel技术制备BST 0-3型厚膜

采用传统高温固相烧结法合成了Ba0.6Sr0.4TiO3(BST)陶瓷粉,并用高能球磨法将其细化为纳米粉,均匀分散于组分相同的BST溶胶中,形成稳定的厚膜先体溶液,而后用匀胶法制备出厚度约为6.5μm的BST厚膜。XRD测试结果表明,650℃热处理后的厚膜为单一钙钛矿相。SEM观测显示厚膜表面均匀一致,无裂纹出现。800℃热处理后的厚膜在室温、频率1kHz下相对介电常数εr和介质损耗tgδ分别为455、0.036。     

Effect of excess TiO2 on the phase evolution and densification of sol-gel derived (Ba,Sr)TiO3 powders

Nanoscaled (Ba_2/3Sr_1/3)Ti_{1 + x} O₃ powders have been prepared by sol-gel technique. Their phase evolution and densification behaviors have been studied by differential thermal analysis (DTA) and high temperature dilatometer, respectively. It is found the addition of 2 mol%-excess amount of TiO₂ lowers the activation energy required for the formation of the perovskite phase by about 130 kJ/mol and thus lowers the crystallization temperature of BST powders. However, the excess amount of TiO₂ makes the nano-powder difficult to sinter. Transmission electron microscopy reveals that a metastable nano-porous layer has formed on the surface of TiO₂-excess nanopowder and this may account for the slow densification rate.