Effect of composition and grain size on dielectric,ferroelectric and induced strain behavior of PLZT/ZrO2 composites

Lead lanthanum zirconate titanate ceramics (PLZT) are well known for their excellent dielectric, piezoelectric and ferroelectric properties. In this study, PLZT 9/70/30, 9/65/35 and 9/60/40 ceramics were prepared by vibro-milling mixed-oxide method. All compositions of powders were uniaxial pressed in pellets and sintered at the temperatures of 1200–1275 °C with various soaking times of 2, 4 and 6 h. The X-ray diffraction (XRD) patterns confirmed that all the PLZT samples had perovskite structure with ZrO₂ as a second phase and PLZT/ZrO₂ composite structure was formed. Dielectric behavior at the frequency of 1 kHz showed broad peak indicating relaxor ferroelectric behavior and the difference of the temperature at maximum dielectric at different frequencies increased when Zr:Ti ratio increased. Polarization with electric field (P-E loop) at room temperature showed that when Zr:Ti ratio increased, the coercive field decreased resulting from crystal structure change from tetragonal to rhombohedral. Induced strain with electric field depended on microstructure where the value of S_max/E_max tended to decrease with increasing grain size. It can be concluded that dielectric and ferroelectric behavior predominantly depended on composition of PLZT ceramics and induced strain behavior predominantly depended on grain size of PLZT ceramics.     

Relaxor Characteristics of the Phase Transformation in (1 − x)BaTiO3–xBi(Zn1/2Ti1/2)O3 Perovskite Ceramics

The single‐phase solid solutions of the (1 ? x)BaTiO₃–(x)Bi(Zn_1/2Ti_1/2)O₃ (BT–BZT) where x = 0.02–0.15 were prepared to investigate dielectric properties. Crystal structure of samples was obtained by using an X‐ray diffraction technique and Raman spectroscopy. For compositions with x ≤ 0.08, the solid solutions exhibited clear tetragonal symmetry and transitioned to pseudocubic symmetry as the content of BZT increased. The dielectric response exhibited a sharp phase transition within the BT‐rich region and the composition 0.92BT–0.08BZT was characterized by the onset of relaxor characteristics. As the concentration of BZT increased, the phase transition exhibited broader and more diffuse behavior. The polarization as a function of electric field (P–E) of these solid solutions also exhibited the same trend. The BT‐rich compositions showed a normal ferroelectric P–E response with a decrease in loop area as the BZT content increased. The composition at x = 0.08 exhibited a pinched hysteresis loop and with further increase in BZT content, the P–E response was characterized by slim loops.     

混合式桥型对超长跨桥梁的适应性

本文对中跨为2500m的混合型斜拉悬索桥的进行了初步设计,构想了三种斜拉悬索桥和一种悬索桥桥式。从初步设计结果中比较它们上部结构钢材的重量发现,考虑到下部结构尺寸,斜拉悬索桥相对悬索桥具有优越性。另外,对这几种型式的桥梁进行了抗弯稳定性分析以及耦合颤振分析。分析结果表明,斜拉悬索桥抗弯稳定性是足够的,而且其临界风速高于悬索桥的临界风速。所以,作者认为针对超长跨度桥梁混合型斜拉悬索桥赛过悬索桥