Effects of sintering temperature on microstructure and electrical properties of 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 modified with CuO

The structural, dielectric and ferroelectric properties of Pb(Mg_1/3Nb_2/3)_0.9Ti_0.1O₃ (PMNT) ceramics prepared with CuO as a sintering aid at various sintering temperatures between 950 °C and 1150 °C are investigated. The lattice parameters slightly increase with the sintering temperature >1050 °C. A significant increase in the grain size is observed when the sintering temperature is increased from 1000 °C to 1050 °C. The maximum dielectric constant reaches the highest value of ∼22,000 for the ceramic sintered at 1050 °C. For the ceramics sintered at >1050 °C, the temperature of maximum dielectric constant and the diffuseness parameters tend to increase with the increasing sintering temperature. The optimal sintering temperature for this ceramic is 1050 °C, which displays significant improvements in ferroelectric properties at room temperature, i.e. the increase in the remanent polarization and the ferroelectric loop squareness.     

Enhanced Dielectric and Ferroelectric Properties of Pb(Mg1/3Nb2/3)0.65Ti0.35O3 Ceramics by ZnO Modification

Phase formation, microstructures, dielectric, and ferroelectric properties of ZnO‐modified Pb(Mg_1/3Nb_2/3)_0.65Ti_0.35O₃ (PMNT/xZnO, where x = 0, 0.4, 2.0, 4.0, and 11.0 mol%) ceramics were studied. A coexistence of rhombohedral and tetragonal ferroelectric phases was observed at room temperature in all samples. The ceramics with the relative densities of 93%–95% were prepared. The modification by ZnO led to an increase in grain sizes of PMNT ceramics. The maximum dielectric constant of the pure PMNT ceramic was increased with x = 0.4–4.0 mol% ZnO doping, with the highest value being observed in the 2.0 mol% sample. Both the temperature at which the transition between rhombohedral and tetragonal ferroelectric phases took place (T_R‐T) and the Curie temperature of the ceramics tended to increase with increasing x. The ferroelectric properties were enhanced with increased remanent polarization and P(E) loop squareness in the compositions with x = 0.4–4.0 mol%. However, the ferroelectric properties were attenuated with x = 11.0 mol%.     

Effects of ZnO nanoparticulate addition on the properties of PMNT ceramics

This research was conducted in order to study the effect of ZnO nanoparticulate addition on the properties of 0.9 Pb(Mg_1/3Nb_2/3)O₃-0.1PbTiO₃ [PMNT] ceramics. The PMNT ceramics were prepared by a solid-state reaction. The ZnO nanoparticles were added into PMNT ceramics to form PMNT/xZnO (x = 0, 0.05, 0.1, 0.5, and 1.0 wt.%). The PMNT/xZnO ceramics were investigated in terms of phase, microstructure, and mechanical and electrical properties. It was found that the density and grain size of PMNT ceramics tended to increase with an increasing amount of ZnO content. Moreover, a transgranular fracture was observed for the samples containing ZnO, while pure PMNT ceramics showed only a intergranular fracture. An addition of only 0.05 wt.% of ZnO was also found to enhance the hardness and dielectric and ferroelectric properties of the PMNT ceramics.     

Proposed Effective Width Criteria for Composite Bridge Girders

In a composite section, in-plane shear strain in the slab (acting as a flange in the composite girder) under the applied bending causes the longitudinal displacements in the parts of the slab remote from the webs to lag behind those near the webs. This phenomenon, termed shear-lag, can result in an incorrect calculation of the displacement and extreme fiber stresses when using only the elementary theory of beam bending. The effective width concept has been introduced, widely recognized, and implemented into different codes of practice around the world as a simplified practical method for design and evaluation of structural strength and stiffness while accounting for shear-lag effects indirectly. Each code implements different ideas and approaches for specifying effective width. This paper proposes simpler and more versatile design criteria for computing the effective width (beff) in steel-concrete composite bridges. A parametric study was conducted based on finite-element analysis of bridges selected by a statistical method—namely, design of experiment concepts. Both simple-span and multiple-span continuous bridges were considered in the parametric study. The finite-element methodology was validated with companion experiments on 1/4- and 1/2-scale specimens. Effective width values at the critical sections were computed from stresses extracted from FEM models and used in developing candidate design equations. The final design criteria were selected based on assessment of impact of candidate equations. Use of full width—the most versatile, simplest, and sufficiently accurate effective width design criteria, is proposed for both positive and negative moment regions.     

A study of flexible piezoelectric generators by sputtering ZnO thin film on PET substrate

Abstract

Flexible technology has recently received much attention in the field of flexible sensors, wearable electronic devices, flexible transparent displays, and energy harvesters. Zinc oxide (ZnO) thin film is the preferred material for use in flexible devices due to its environmental friendliness, high electrical performance and low synthesis temperature. In addition, ZnO possesses a non-centrosymmetric crystal structure, causing a piezoelectric effect in the material. This work presents the fabrication of flexible piezoelectric generators using the deposition of ZnO on a PET substrate using sputtering techniques. The fabricated flexible generators are capable of generating an output power of 14 µW through an optimal resistive load of 750 kΩ. An output voltage of 2.00 Vp and a current of 150 μA measured across a 750 kΩ resistor were subsequently obtained.     

Effects of CuO nanoparticles addition on properties of PMNT ceramics

This research investigates the role of CuO nanoparticles addition on properties of 0.9PMN–0.1PT (PMNT) ceramics. Phase purity, density, microstructure, dielectric and ferroelectric properties of the ceramics were investigated. The density of the ceramics reaches a maximum when 0.5 wt% of CuO is added into the ceramics while grain size of the ceramics tends to increase with the increase in CuO content. ε_max of the ceramics tends to increase with increasing CuO concentration. The improvement of P_r of the ceramics is observed in the ceramic incorporated with over 0.1 wt% of CuO.     

Effective Slab Width Definition for Negative Moment Regions of Composite Bridges

Currently, the AASHTO-LRFD design code specifies the same effective slab width design criteria for both positive moment sections and negative moment sections. The only difference in computing effective slab width between the positive and negative moment regions is the value of effective span length (Le), the definition of which is problematic. The effective slab width concept for the positive moment regions has been investigated by many researchers. However, the classical effective slab width definition does not take into account both the strain variation through the slab thickness and the mechanism that redistributes load from concrete to steel reinforcement after cracking. In this paper, a more robust effective slab width definition for the negative moment section is introduced to account for these factors. The proposed definition is developed for negative moment regions and explored by using the finite-element method (FEM). The finite-element modeling scheme is briefly discussed, and the model is successfully verified with experimental results. Numerical results show the simplicity, accuracy, and robustness of the proposed definition in extracting effective slab width values from FEM results. Numerical results also indicate that the effective slab width criteria in the current AASHTO-LRFD Specifications is typically conservative for larger girder spacings. Detailed calculations of effective slab width for the negative moment regions using the proposed definition are summarized at the end of this paper.     

Fabrication and characterization of flexible piezoelectric composites with natural rubber matrix

Abstract

This work aims to fabricate and characterize flexible piezoelectric composites with natural rubber (NR) matrix. Different amounts of Pb(Mg_1/3Nb_2/3)_0.65Ti_0.35O₃ (PMNT) powders were added in NR matrices. Porosity, tensile strength and percent elongation at break of composites tended to decrease with increasing PMNT content. The dielectric constant of the NR materials was found to be 3.5. It was raised up to 4.2, 5.0, 4.5, 4.8 and 5.1 when 60, 80, 100, 120 and 150 phr PMNT powders were added. However, dielectric loss of NR materials did not change with PMNT additions. Among this composite system, the NR/100PMNT composite showed the best piezoelectric properties, which its output voltage, piezoelectric coefficient (d₃₃) and piezoelectric voltage coefficient (g₃₃) values were equal to 1.61 V, 2.1?×?10^?4 pC/N and 5.4?×?10^?6 V?m/N, respectively. This composition composite is a promising material suitable for further improvement to be used as piezoelectric generators in energy harvesting applications.     

Effect of ZnO nano-particulate modification on properties of PZT–BLT ceramics

This research was conducted to study the effect of ZnO nano-particulate modification on properties of Pb(Zr_0.52Ti_0.48)O₃ (PZT)–(Bi_3.25La_0.75)Ti₃O₁₂ (BLT) ceramics prepared by a mixed-oxide solid-state sintering method. ZnO nano-particulate was added into PZT–BLT ceramics to obtain PZT–BLT/xZnO (x = 0, 0.1, 0.5 and 1.0 wt%). The PZT–BLT/xZnO ceramics were investigated in terms of phase, microstructure, physical, electrical, and mechanical properties. Tetragonality of PZT–BLT crystal structure tended to increase with increasing ZnO content. ZnO addition obviously increased the density of PZT–BLT ceramics while the grain size slightly decreased. Intergranular fracture mode was observed for pure PZT–BLT ceramic while the samples contained ZnO nano-particles showed a mixed-mode inter-/trans-granular fracture. Addition of ZnO also affected hardness and fracture toughness values. Addition of ZnO nano-particulate into PZT–BLT ceramics was found to improve room temperature dielectric constant but did not have a significant effect on ferroelectric properties. These observed results were expected to be caused by the behaviors similar to a donor-doped system.