Electromechanical Properties of PMN–PZT Piezoelectric Single Crystals Near Morphotropic Phase Boundary Compositions

Pb(Mg_1/3Nb_2/3)O₃–PbZrO₃–PbTiO₃ (PMN–PZT) ferroelectric single crystals near morphotropic phase boundary compositions were fabricated by solid-state crystal growth. The Curie temperatures ( T _C) of the grown PMN–PZT crystals were found to be on the order of 210°C, with ferroelectric phase transition temperatures ( T _{R – T} ) in the range of 96°–165°C. The electromechanical coupling factors k ₃₃ and k ₃₂ were found to be >90% and >−87%, respectively. The coercive field E _C for all the compositions was on the order of 5 kV/cm, double the value of pure Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PMNT) crystals. The temperature dependence of the piezoelectric and electromechanical properties and dc bias effect on the dielectric behavior were investigated. The temperature usage range under dc bias was found to be improved when compared with pure PMNT crystals with similar piezoelectric properties.     

A study on the optimum design of high-speed low-floor bogie with independently rotating wheels

The low-floor bogie is a prior technology in countries and companies that want to develop the tram. The Low-floor tram (LFT), which includes low-floor bogies, is easy to embark and disembark because of the low floor height. In addition, it can be driven on urban as well as rural tracks. Furthermore, emissions such as NOx and SOx can be reduced. Due to these advantages, this innovative technology is expected to change the public transport system. To improve utilization in a downtown area, the technology for the low-floor bogie should satisfy conditions of a high-speed of over 80 km/h and minimum radius within a 25 mR curve for smooth running on a track that has a severe turning radius. Moreover, the wheelset should not be located in the bogie, and the components inside the bogie need to be wellarranged to satisfy the full low-floor condition. In this study, to develop an over-80 km/h class high-speed low-floor bogie that can be driven safely on a 25 mR curved track, a conceptual design of the LFT multibody dynamics model was constructed and dynamic characteristics were assessed by dynamic analysis. The modeling modification with Independently rotating wheels (IRW) needed to steer actively through semi-active suspension and the optimization using Design of experiments (DOE) were then performed. Through DOE method, the optimum combination of design parameters could be obtained and, the driving performances such as ride stability, comfort and safety of the LFT could then be improved about 7 %. The results of this work are available to detail design and development of LFT.     

Effect of Grain Coalescence on the Abnormal Grain Growth of Pb(Mg1/3Nb2/3)O3-35 mol% PbTiO3 Ceramics

Abnormal grain growth (AGG), which occurred during the heat treatment of Pb(Mg_1/3Nb_2/3)O₃-35 mol% PbTiO₃ (PMN-35PT) with excess PbO, was investigated. AGG has been suggested to be the consequence of grain coalescence that results in the formation of Σ3 coincidence site lattice and low angle grain boundaries. Because of reentrant edges appearing at the ends of these boundaries, the coarsening rate of grains was significantly enhanced and AGG occurred.     

Object recognition algorithm using a vocabulary tree and a pre-matching array

A vocabulary tree algorithm builds a tree structure with the off-line learning method using a large training image dataset. After constructing the tree structure, we can retrieve a query image class very quickly by searching it. This algorithm has come into the spotlight recently because of the great reduction in computation time. In this article, we suggest a method which improves the classification accuracy by searching a vocabulary tree many times for each test dataset. The information which is given by the pre-matching array determines how the tree is visited. Using our new algorithm, we can reduce the miss-classification rate considerably. On the other hand, losses in computation time and memory allocation are negligible with respect to real-time recognition.     

A study on the development of a web based urban transit reliability evaluation system

Over the past twenty years, the maintenance system developed, and its importance increased. For the effective maintenance, the maintenance system has been developed by introducing the concept of RCM (Reliability Centered Maintenance). This research is to develop an effective maintenance system for urban transit based on the concept of RCM. RCM is a systematic approach to develop a cost-effective maintenance strategy based on the various components’ reliability of the subject system. The final process of RCM determines appropriate failure maintenance strategies. For realization of RCM, reliability evaluation framework has been studied to compute the reliability index for urban transit. The framework requires the following processes: BOM (Bill of Materials), RBD (Reliability Block Diagram) based on FBD (Function Block Diagram), and failure code classification. The goal of this paper is to define the maintenance procedure for the subject system since successful maintenance system depends on an automated maintenance plan. This plan can be scheduled effectively by collecting and analyzing data from maintenance experience. For doing this, this paper proposes the web-based maintenance system for collecting data and the computing of MTBF (Mean Time between Failures) at the maintenance stage for analyzing data.     

Solid state crystal growth of BiScO3-Pb(Mg1/3Nb2/3)O3-PbTiO3

Single crystals 0.26BiScO₃-0.25Pb(Mg_1/3Nb_2/3)O₃-0.49PbTiO₃ [BSPMNT] have been grown for the first time by the solid-state crystal growth (SSCG) method. A <110> oriented Ba(Zr,Ti)O₃ crystal seed was embedded in a matrix of BSPMNT compact which was annealed at high temperatures to induce the single crystal growth. Various fluxes, including Bi₂O₃, LiBiO₂, PbO/LiBiO₂, and PbO/Bi₂O₃, were used and their effects on the microstructure of the annealed compacts and the single crystal growth behavior were investigated. In the annealed samples with PbO/Bi₂O₃ flux, a considerable single crystal growth occurred at 1050?°C (with thickness on the order of 500?C1000???m), without the formation of abnormally large grains in the matrix. The results were explained in terms of the effect of various fluxes, based on the grain growth theory.     

Direction of Liquid Film Migration Induced by Chromic Oxide in Alumina-Anorthite

Three kinds of single-crystalline alumina plates with the crystallographic planes of C, m, and R were diffusion-bonded with liquid-phase sintered (98)alumina-(2)anorthite (in wt%) plates (P) and then heat-treated at 1600°C under a Cr₂0₃-containing atmosphere. During the heat treatment, for all of the specimens studied, the anorthite liquid films between alumina plates migrated to grains with surface orientation corresponding to higher coherency strain energy. This result is in better agreement with a prediction based on the coherency strain theory than the previous one obtained for grain-boundary migration. The discrepancy between the predicted and previously observed migration directions of some grain boundaries in alumina may therefore be attributed to an effect of grain-boundary structure and stress transmission across the boundary.     

Grain Growth Control and Solid-State Crystal Growth by Li2O/PbO Addition and Dislocation Introduction in the PMN–35PT System

Grain growth behavior and solid-state single crystal growth (SSCG) in the Pb(Mg_1/3Nb_2/3)O₃–35 mol% PbTiO₃ (PMN–35PT) system have been investigated with varying Li₂O/PbO ratios. The effect of dislocation density on crystal growth has also been studied. For SSCG, a BaTiO₃ single-crystal seed was embedded in a polycrystalline PMN–PT matrix. During annealing, a PMN–PT single crystal grew from the seed at the cost of the small matrix grains. Addition of Li₂O dopant first enhanced and then reduced abnormal grain growth in the matrix. In the 2 mol% Li₂O and 6 mol% PbO excess PMN–PT samples annealed at 1200°C, considerable single-crystal growth occurred without formation of abnormally large grains in the matrix. Increasing the dislocation density in the BaTiO₃ seed crystal resulted in enhanced growth of single crystals. These results were explained in terms of interface reaction-controlled nucleation and growth, based on crystal growth theories.     

Elastic, Piezoelectric, and Dielectric Properties of 0.71Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 Crystals Obtained by Solid-State Crystal Growth

Single crystals with the composition of 0.71Pb(Mg_1/3Nb_2/3)O₃–0.29PbTiO₃ (PMNT29) were grown using the solid-state crystal growth (SSCG) method. Compared with the conventional Bridgman grown crystals, the SSCG PMNT29 crystals were found to possess comparable piezoelectric, dielectric, and electromechanical properties ( d ₃₃∼1500 pC/N, ɛ^T ₃₃/ ɛ ₀∼5400 and k ₃₃∼90%), with the same Curie temperature ( T _C) and ferroelectric phase transformation temperature ( T _{R – T} ). The full set of elastic, piezoelectric, and dielectric material constants were determined by the resonance method for the SSCG grown PMNT29 crystals according to IEEE standards and compared with Bridgman grown crystals. The dielectric temperature behavior and the strain field characteristics were investigated, demonstrating excellent performance over the temperature range from room temperature to 95°C. Strain behavior at high electric fields was found to be different from Bridgman growth crystals and believed to be attributed to different domain structures.     

Diffusion-Induced Interface Migration and Mechanical Property Improvement in the Lead Magnesium Niobate–Lead Titanate System

Diffusion–induced interface migration (DIIM) is a technique for modifying the microstructure and mechanical properties of ceramics. In the present study, we investigated DIIM in 0.65Pb(Mg_1/3Nb_2/3)O₃·0.35PbTiO₃ (mol fraction) (PMN–PT) ceramics and its effect on mechanical properties. PMN–PT samples were fabricated using the Columbite precursor method and then surface–modified by heat treatment after packing with PbTiO₃ powder to induce DIIM. Evaluation of mechanical properties using Hertzian indentation and Vickers indentation showed that the critical load for yielding and surface hardness of the PbTiO₃–packed PMN–PT samples were higher than those of the unpacked samples. Thus, the mechanical properties were improved in the samples with a DIIM layer. These results showed that the reliability of mechanical properties of PMN–PT samples is improved by inducing DIIM at the surface.