Search

A novel lead-free tungsten bronze type ceramic Sr5BiTi3Nb7O30, was prepared by a conventional solid-state reaction route. The room-temperature crystal structure shows an average structure with centro-symmetric space group P4/mbm identified by synchrotron XRD. Temperature dependence of dielectric permittivity indicates that Sr5BiTi3Nb7O30 is a ferroelectric relaxor with Tm near 260 K. The ceramic displays stronger frequency dispersion and lower phase-transition temperature compared with Sr6Ti2Nb8O30. A macroscopic and phenomenological statistical model was employed to describe the temperature dependence of their dielectric responses. The calculated size of polar nanoregions (PNRs) of Sr5BiTi3Nb7O30 compared with Sr6Ti2Nb8O30 implies that the stronger diffusion phase transition for the former is related to the disorder emerged in both A and B sites. The smaller PNRs can be activated at lower temperature but have smaller electrical dipole moment. This is the origin of relaxor behavior of Sr5BiTi3Nb7O30 with lower Tm and dielectric permittivity. The PNRs is related to a local structure with a polar space group P4bm, which contributes to the dielectric frequency dispersion of relaxor behavior. This work opens up a promising feasible route to the development of relaxor ferroelectrics in tungsten bronze type oxides.

Journal of applied physics 131(16), 164102 (2022). doi:10.1063/5.0084417, This paper reports a novel lead-free tungsten bronze type ceramic, Sr$_5$BiTi$_3$Nb$_7$O$_{30}$, prepared by a conventional high-temperature solid-state reaction route. The crystal structure identified using synchrotron x-ray diffraction data and Raman spectroscopy for Sr$_5$BiTi$_3$Nb$_7$O$_{30}$ could be described as an average structure with the centrosymmetric space group P4/mbm and a local non-centrosymmetric structure at room temperature. In the second-harmonic generation measurement, the Sr$_5$BiTi$_3$Nb$_7$O$_{30}$ compound exhibits second-order nonlinear optical behavior, which suggests the material is ferroelectric. Temperature dependence of the dielectric permittivity indicates that the dielectric anomaly in Sr$_5$BiTi$_3$Nb$_7$O$_{30}$, associated with the disorder on the A and B sites, results in strong frequency dispersion with a low phase-transition temperature. A macroscopic and phenomenological statistical model was employed to describe the temperature dependence of the dielectric responses of Sr$_5$BiTi$_3$Nb$_7$O$_{30}$ and Sr$_6$Ti$_2$Nb$_8$O$_{30}$. The calculated sizes of polar nanoregions for both compounds imply structural disorder induced by A and B sites, giving rise to a more diffuse ferroelectric transition for Sr$_5$BiTi$_3$Nb$_7$O$_{30}$. The smaller polar nanoregions with smaller electrical dipole moments can be activated at lower temperatures, leading to Sr$_5$BiTi$_3$Nb$_7$O$_{30}$ having a lower Tm (∼260 K) than other tungsten bronze type ferroelectrics. This work charts a promising feasible route to the development of improved relaxor ferroelectrics in tungsten bronze type oxides., Published by American Inst. of Physics, Melville, NY

Bacterial adhesion and bile sludge accumulation can increase the risk of complications such as stent restenosis after biliary stent implantation. Compared with active and passive antimicrobial surfaces, a significant advantage of slippery liquid-infused porous surfaces (SLIPSs) is their recoverable anti-adhesive properties. According to the mechanism of SLIPSs and the application environments of the biliary system, a polytetrafluoroethylene (PTFE) electrospun fibrous membrane-impregnated silicone-oil system was developed to construct an ultrasmooth surface. Experimental results indicated that a PTFE SLIPS with 350 cSt of silicone oil had an extremely small roll angle (5°) and a high slip rate (4.8 ± 0.1 mm/s) and maintained excellent sliding stability after 7 d of immersion in model bile system. Thus, it can inhibit the adhesion of proteins, Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli, and bile sludge. Moreover, when human fibroblasts were cultured on the PTFE SLIPS, it exhibited good cytocompatibility. Therefore, the proposed ultrasmooth PTFE membranes provide a promising alternative for biliary system to prevent bacterial adhesion and bile sludge accumulation.

Periosteum plays a pivotal role in bone formation and reconstruction. The ideal repair process for critical-size bone defects with periosteum damage is to induce regeneration of periosteum tissue and the subsequent bone regeneration derived by the periosteum. Inspired by the bilayer structure of the natural periosteum, we develop a periosteum structure/function dual mimicking membrane for the

The existence of polar nanoregions is the most important characteristic of ferroelectric relaxors, however, the size determination and dynamic of PNRs remains uncertain. We reveal a re-entrant relaxor behavior and ferroelectric-paraelectric transition coexists in complex perovskite oxide 0.6Bi(Mg1/2Ti1/2)O3-0.4PbTiO3. Two dielectric anomalies (i) the low-temperature re-entrant relaxor transition and (ii) the high-temperature diffuse phase transition (DPT) were described by the phenomenological statistical model. The sizes of the two kinds of polar nanoregions (PNRs) corresponding to two ferroelectric states were obtained. The dynamic of PNRs were analyzed using isothermal electrical modulus, which shows three critical temperatures associated with the diffuse phase transition, the formation and freezing of PNRs, respectively. The temperature evolution of the PNRs evolution depends on the stoichiometry of bismuth. The results provide new insights into the dynamic behavior of PNRs and the modification way of re-entrant relaxor behavior., Comment: 29 pages, 9 figures, 4 tables

A steel strand is widely used in long span prestressed concrete bridges. The safety and stability of a steel strand are important issues during its operation period. A steel strand is usually subjected to various types of prestress loss which loosens the anchorage system, negatively impacting the stability of the structure and even leading to severe accidents. In this paper, the authors propose a wavelet packet analysis method to monitor the looseness of the wedge anchorage system by using stress wave-based active sensing. As a commonly used piezoceramic material, lead zirconate titanate (PZT) is employed with a strong piezoelectric effect. In the proposed active sensing approach, PZT patches are used as sensors and actuators to monitor the steel strand looseness. The anchorage system consists of the steel strand, wedges and barrel, which forms two different direct contact surfaces to monitor the tension force. PZT patches are pasted on the surface of each steel strand, corresponding wedge and barrel, respectively. Different combinations of PZTs are formed to monitor the anchoring state of the steel strand according to the position of the PZT patches. In this monitoring method of two contact surfaces, one PZT patch is used as an actuator to generate a stress wave and the other corresponding PZT patch is used as a sensor to detect the propagated waves through the wedge anchorage system. The function of these two PZTs were exchanged with the changing of transmission direction. The wavelet packet analysis method is utilized to analyze the transmitted signal between PZT patches through the steel strand anchorage system. Compared with the wavelet packet energy of received signals under different PZT combinations, it could be found that the wavelet packet energy increased with the increasing of anchorage system tightness. Therefore, the wavelet packet energy of received signal could be used to monitor the tightness of the steel strand during operation. Additionally, the wavelet packet energy of the received signals are different when the same PZT combination exchanges the energy transfer direction. With the comparison on the received signals of different combinations of PZTs, the optimal energy transfer path corresponding to different contact surfaces of the steel strand could be determined and the optimal experimental results are achieved.

Periosteum plays a pivotal role in bone formation and reconstruction. The ideal repair process for critical-size bone defects with periosteum damage is to induce regeneration of periosteum tissue and the subsequent bone regeneration derived by the periosteum. Inspired by the bilayer structure of the natural periosteum, we develop a periosteum structure/function dual mimicking membrane for the in-situ restoration of periosteum and bone tissue. Among them, the macroporous fluffy guiding layer (TPF) simulates the fibrous layer of the natural periosteum, which is conducive to infiltration and oriented growth of fibroblasts. And the extracellular matrix-like bioactive layer (TN) simulates the cambium layer of the natural periosteum, which significantly enhances the proliferation and osteogenic differentiation of rat bone marrow mesenchymal stem cells. A middle dense layer (PC) connects the above two layers and has the function of preventing the invasion of soft tissues while enhancing the biomimetic periosteum. In vivo restoration results show that the tri-layer biomimetic periosteum (TPF/PC/TN) has an outstanding effect in promoting the regeneration of both vascularized periosteum and bone at the same time. Therefore, the enhanced biomimetic periosteum developed in this research has a great clinical value in the efficient and high-quality reconstruction of critical-size bone defects with periosteum damage.

Steel strands are widely used in cable stay or suspension bridges. The safety and stability of steel strands are important issues during their operation period. Steel strand is subjected to various types of prestress loss which loosens the wedge anchorage system, negatively impacting the stability of the structure and even leading to severe accidents. In this paper, the authors propose a time reversal (TR) method to monitor the looseness status of the wedge anchorage system by using stress wave based active sensing. As a commonly used piezoceramic material, Lead Zirconate Titanate (PZT) with a strong piezoelectric effect is employed. In the proposed active sensing approach, PZT patches are used as sensors and actuators to monitor the steel strand looseness status. One PZT patch is bonded to the steel strand, one PZT patch is bonded to the wedges, and another PZT patch is bonded to the barrel. There are three different interfaces of the wedge anchorage system to monitor the steel strand looseness status. In the first method, the PZT patch on the steel strand is used as an actuator to generate a stress wave and the PZT patch on the wedge is used as a sensor to detect the propagated waves through the wedge anchorage system. In the second method, the PZT patch on the steel strand is used as an actuator to generate a stress wave and the PZT patch on the barrel is used as a sensor to detect the propagated waves through the wedge anchorage system. In the third method, the PZT patch on the wedges is used as an actuator to generate a stress wave and the PZT patches on the barrel is used as a sensor to detect the propagated waves through the wedge anchorage system, of which the looseness will directly impact the stress wave propagation. The TR method is utilized to analyze the transmitted signal between PZT patches through the wedge anchorage system. Compared with the peak values of the TR focused signals, it can be found that the peak value increases as the wedge anchorage system tightness increases. Therefore, the peak value of the TR focused signal can be used to monitor the tightness of the steel strand. In addition, the experimental results demonstrated the time reversal method&rsquo, s reliability, sensitivity and anti-noise property.

The fabrication and erection of cable-stayed bridges involve major changes in structure configuration through the addition and removal of structure components. In every stage of the construction process, adequate information on the constructed structure is important to determine the real structure situation for the analysis of errors and to verify construction requirements. The ultimate goals are to meet construction needs and identify the effects of modification in subsequent construction procedures. The final configuration of the structure is strongly dependent on the construction and fabrication procedures. In this regard, developing an FEA model to simulate the actual construction processes is necessary to determine the performance of a bridge under external loads. In this study, a general methodology for construction processes is presented to simulate a cable-stayed bridge. The stage-by-stage construction of the Sutong Bridge is simulated with ANSYS software package. The tensions of cables are realized with ANSYS parametric design language, element birth and death function, and mutliframe restart function. The objective of the construction stage simulation is to identify stresses and deformations of the steel box girder and the concrete towers, as well as the cable tension stress, to meet the design requirements. Results of the construction stage analysis showed that the temperature method could simulate the adjustment of the inclined cable force successfully, and the global stiffness of the Sutong Bridge was very small before closure. These findings served as the initial data for a dynamic research on the Sutong cable-stayed bridge.

CaCu$_{3}$Ti$_{4}$O$_{12}$ (CCTO) has a large dielectric permittivity that is independent of the probing frequency near the room temperature, which complicated due to the existence of several dynamic processes. Here, we consider the combined effects of localized charge carriers (polarons) and thermally activated charge carriers using a recently proposed statistical model to fit and understand the permittivity of CCTO measured at different frequencies over the whole temperature range accessible by our experiments. We found that the small permittivity at the lowest temperature is related to polaron frozen, while at higher temperatures the rapid increase is associated with the thermal excitation of polarons inducing the Maxwell-Wagner effect, and the final increase of the permittivity is attributed to the thermally activated conductivity. Such analysis enables us to separate the contributions from localized polarons and conductive charge carriers and quantify their activation energies.

Journal of the European Ceramic Society 37(4), 1387 - 1399 (2017). doi:10.1016/j.jeurceramsoc.2016.11.024, tPhase diagram of the solid solution system K$_{0.5}$Na$_{0.5}$NbO$_{3}$-Bi$_{½}$Na$_{½}$TiO$_{3}$[(1-x)KNN-xBNT] has beenestablished from dielectric permittivity measurement and structure analyses. The unit cell volumescontinuously decrease depending on the composition, while the local structure maintains distortionsaway from the cubic average structure in the range 0.10 ≤ x ≤ 0.90. No clear correspondence for thetemperatures of phase transition exists between structural studies and physical properties. The dielec-tric behavior is depicted successively from normal ferroelectric, diffuse phase transition, re-entrant-likerelaxor, relaxor + dipolar glass-like relaxor, BNT-like relaxor with the increase of BNT. A comprehensivecomposition-property phase diagram for this system has been given to understand the various ferro-electric phenomena. The result could be mainly elucidated by the nanoclusters and the disorder drivennucleation of polar nanoregions contributed by a valence mismatch at one of the cation sites., Published by Elsevier Science, Amsterdam [u.a.]

epl 118(4), 47001 (2017). doi:10.1209/0295-5075/118/47001, The correspondence between the temperature dependence of phase structures and the experimental physical properties was made clear for the first time in the Bi$_{1/2}$Na$_{1/2}$TiO$_3$ system according to in situ XRD, in situ Raman and impedance spectroscopy. XRD profiles show pseudo-cubic symmetry independent of temperature, while one of the Raman models disappears near 620 K, indicating that the local symmetry increases. The temperature dependence of the main relaxation time of the electric modulus spectra can be divided into four regions, characterizing the thermal evolution of polar nanoregions (PNRs) with different symmetries and a phase transition between rhombohedral and tetragonal symmetry. Therefore, the relaxation times of the electric modulus provide a way to estimate the local phase transition and the thermal evolution of R3c and P4bm PNRs., Published by EDP Sciences, Les-Ulis

epl 114(4), 47011(2016). doi:10.1209/0295-5075/114/47011, The nature of the cubic-like state in the lead-free piezoelectric ceramics 0.5K$_{0.5}$Na$_{0.5}$NbO$_{3}$-0.5Na$_{1/2}$Bi$_{1/2}$TiO$_{3}$ (KNN-50BNT) has been examined in detail by synchrotron x-ray diffraction (SD), selected-area electron diffraction (SAED), neutron diffraction (ND), and temperature-dependent dielectric characterization. The SD pattern of KNN-50BNT presents a pure perovskite structure with pseudocubic symmetry. However, superlattice reflections were observed by SAED and completely indexed by tetragonal symmetry with P4bm space group in ND pattern. The relaxor behavior of KNN-50BNT is compared with Pb-based and Ba-based relaxors and discussed in the framework of the Vogel-Fulcher law and the new glass model. The KNN-50BNT ceramic exhibits the strongest dielectric dispersion among them., Published by EDP Science8268, Les-Ulis

Journal of applied crystallography 49(2), 574 - 584(2016). doi:10.1107/S1600576716002909, The phase diagram of the lead-free piezoelectric $(1 - x)K_{0.5}Na_{0.5}NbO_{3}-xBi_{1/2}Na_{1/2}TiO_{3}$ system has been studied by high-resolution synchrotron powder diffraction, neutron powder diffraction and selected area electron diffraction. The two lead-free piezoelectric materials $K_{0.5}Na_{0.5}NbO_{3}$ and $Bi_{1/2}Na_{1/2}TiO_{3}$ form an infinite substitution solid solution. The orthorhombic (O), monoclinic (M), tetragonal (T) and rhombohedral (R) phases and the phase coexistence of M (Pm) + T (P4mm) for 0.02 < x $\leq$ 0.14, T (P4bm) + pseudocubic $(Pm\overline{3}m)$ for 0.14 < x $\leq$ 0.87 and T (P4bm) + R (R3c) for 0.87 < x $\leq$ 0.96 have been investigated at room temperature, with a subtle change in the structure observed. The oxygen octahedral tilt system has been mapped as a function of composition and temperature. The results indicate that $K_{0.5}Na_{0.5}NbO_{3}-Bi_{1/2}Na_{1/2}TiO_{3}$ does not display a morphotropic phase boundary like lead zirconate titanate, and that the most significant structural changes as a function of composition occur near x = 0.14 and x = 0.87 as a result of ionic disorder at the A and B sites in the perovskite $ABO_{3}$ structure at room temperature., Published by Munksgaard, Copenhagen

The phase diagram of the lead-free piezoelectric $(1 - x)K_{0.5}Na_{0.5}NbO_{3}-xBi_{1/2}Na_{1/2}TiO_{3}$ system has been studied by high-resolution synchrotron powder diffraction, neutron powder diffraction and selected area electron diffraction. The two lead-free piezoelectric materials $K_{0.5}Na_{0.5}NbO_{3}$ and $Bi_{1/2}Na_{1/2}TiO_{3}$ form an infinite substitution solid solution. The orthorhombic (O), monoclinic (M), tetragonal (T) and rhombohedral (R) phases and the phase coexistence of M (Pm) + T (P4mm) for 0.02 < x $\leq$ 0.14, T (P4bm) + pseudocubic $(Pm\overline{3}m)$ for 0.14 < x $\leq$ 0.87 and T (P4bm) + R (R3c) for 0.87 < x $\leq$ 0.96 have been investigated at room temperature, with a subtle change in the structure observed. The oxygen octahedral tilt system has been mapped as a function of composition and temperature. The results indicate that $K_{0.5}Na_{0.5}NbO_{3}-Bi_{1/2}Na_{1/2}TiO_{3}$ does not display a morphotropic phase boundary like lead zirconate titanate, and that the most significant structural changes as a function of composition occur near x = 0.14 and x = 0.87 as a result of ionic disorder at the A and B sites in the perovskite $ABO_{3}$ structure at room temperature.