16 results on '"Feifei Wang"'
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2. Improved rectification characteristics of the GR/Blue P/GR selector by doping: First-principles study
- Author
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Feifei Wang, Yuehua Dai, Cheng Ding, Bing Yang, Xing Li, and Lin Jin
- Subjects
General Physics and Astronomy - Abstract
In this paper, a graphene (GR)/monolayer (ML) blue phosphorous (Blue P)/GR selector was studied based on the first-principles theory. Due to different contact edges, four GR–Blue P lateral heterojunctions were constructed, namely, armchair–armchair (A–A), zigzag–armchair (Z–A), armchair–zigzag (A–Z), and zigzag–zigzag (Z–Z). As demonstrated by the binding energy and Mulliken population, we found that the Z–Z heterojunction was relatively stable. Furthermore, a GR/Blue P/GR selector based on the Z–Z heterojunction interface was proposed with a nonlinear (NL) coefficient is 105. However, the drive current of this device was insufficient. A P atom of the resistive layer was separately substituted with four different atoms (Ni, Cu, N, and Cl) to effectively improve selector performance. The energy band structure was half-metallic when doped with Ni or Cu while the others still maintained semiconductor characteristics, and the bandgap was significantly reduced. The Schottky barrier height and width of the interface (GR–Blue P), with Cl as the substituted impurity, were the smallest, leading to a three order of magnitude increase in the NL coefficient. The calculation shows that GR/Blue P/GR devices can be integrated as selectors in Resistive switching Random Access Memory (RRAM) arrays. This work also has a certain guiding significance for manufacturing new types of two-dimensional lateral selector apparatuses.
- Published
- 2022
- Full Text
- View/download PDF
3. Effects of undercooling on atomic crystallization behaviors and growth mechanisms of pure metals
- Author
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Zhenzhen Yan, Bin Xu, Feifei Wang, Jinfu Li, and Ling Ti Kong
- Subjects
General Physics and Astronomy - Abstract
The atomic crystallization behaviors at the crystal–melt interfaces in a broad range of undercoolings are investigated by molecular dynamics simulations for two representative pure metals, FCC Cu and BCC Ta. Results show that the atomic transformation displacements against temperature for both metals have the same trend, i.e., increasing significantly as temperature goes up at small undercooling and keeping invariant at large undercooling. By classifying the interfacial atomic attachment behaviors into ballistic and diffusive motions based on the displacement analysis, it is found that the crystal growth of both metals involves many ballistic attachments, and a small increment of diffusive attachments at the Ta interface leads to a significant energy barrier for crystallization comparing to that of Cu. The temperature effects on the interfacial structures and atomic dynamics to attach onto the crystal are also studied in detail, and their correlations with the different growth mechanisms at low and deep undercoolings are disclosed. Finally, the crystallization rate is proved to be dominated by the atomic transformation displacement and interfacial atomic movement rate for either metal, rather than the atomic thermal velocity or liquid diffusion coefficient.
- Published
- 2022
- Full Text
- View/download PDF
4. A model of TaOx threshold switching memristor for neuromorphic computing
- Author
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Xing Li, Zhe Feng, Jianxun Zou, Xu Wang, Guyue Hu, Feifei Wang, Cheng Ding, Yunlai Zhu, Fei Yang, Zuheng Wu, and Yuehua Dai
- Subjects
General Physics and Astronomy - Abstract
In this article, we analyzed the experimental data based on the TaOx memristor and found that the threshold switching (TS) characteristics are related to temperature, and its logarithmic I–V curve is in good agreement with the space charge limiting current conduction mechanism. We use this mechanism to establish a TS physical model and then use the physical model to build an LTspice model. The model data are fitted with the experimental data, which is basically consistent. Next, using the TS memristor to simulate a leaky integrate-and-fire neuron circuit, the basic dynamics are realized. By changing the external temperature of the memristor, the output frequency of the neuron will be more intense as the temperature increases. Finally, an artificial spiking neural network (SNN) was built based on this neuron circuit for MNIST recognition task. In this SNN, the input signals fused both voltage amplitude and temperature to achieve neuromorphic multimodal preprocessing and enhance the recognition accuracy. These results demonstrated the reliability of the model, which enhanced the flexibility for exploring the application of TaOx-based TS memristors.
- Published
- 2022
- Full Text
- View/download PDF
5. Temperature dependent size effects on crystal growth of nanorods revealed by molecular dynamics simulations
- Author
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Lingti Kong, Mingxu Wang, Risheng Wang, Feifei Wang, Gong-Ji Yang, and Jinfu Li
- Subjects
010302 applied physics ,Work (thermodynamics) ,Materials science ,General Physics and Astronomy ,Crystal growth ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Kinetic energy ,01 natural sciences ,Molecular dynamics ,Chemical physics ,0103 physical sciences ,Phenomenological model ,Nano ,Thermal stability ,Nanorod ,0210 nano-technology - Abstract
Nano metallic materials are promising candidates in many engineering applications, whereas their thermal stability is generally of great concern. In this study, molecular dynamics simulations were performed to study the crystal growth process of CuZr nanorods with different diameters. An appreciable size effect was observed in the crystal growth rates. However, the trend of size dependence could be reversed by changing the temperature. For temperatures above 925 K, nanorods of smaller diameters grow slower than those with larger diameters, while for temperatures below 925 K, smaller nanorods grow faster. It turns out that the temperature dependent size effect originates from the competition between the thermodynamic and kinetic factors. Atoms in the surficial region of the nanorods have higher mobility while lower thermodynamic driving force for growth than those in the interior. Under different temperatures, the overwhelming factor varies, leading to the temperature dependent size effect. A phenomenological model was proposed accordingly to describe the size dependence, which is found to work well under all temperatures explored.
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- 2021
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6. Elastic, piezoelectric, and dielectric properties of tetragonal Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals
- Author
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Chongjun He, Dan Zhou, Feifei Wang, Haiqing Xu, Di Lin, and Haosu Luo
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Physics - Abstract
A study determined the elastic, piezoelectric, and dielectric properties of tetragonal 0.65Pb(Mg1/3Nb12/3)O3-0.35PbTiO3 (PMN-35%PT) single crystals. The PMN-35%Pt crystals were found to have much more phase structure to Curie temperature, as compared with the crystals with compositions in the morphotropic phase boundary, which makes them promising materials for high power applications in fabricating transducers, actuators, and generators.
- Published
- 2006
7. A first-principles study of interfacial fluorination at the HfO2/Al2O3 interface in charge trapping memory devices
- Author
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Yuehua Dai, Feifei Wang, Wenjuan Lu, Cheng Ding, and Lanzhi Dong
- Subjects
010302 applied physics ,Materials science ,Passivation ,Interface (computing) ,General Physics and Astronomy ,02 engineering and technology ,Trapping ,021001 nanoscience & nanotechnology ,01 natural sciences ,Chemical physics ,Ab initio quantum chemistry methods ,Covalent bond ,0103 physical sciences ,Degradation (geology) ,Thermal stability ,Density functional theory ,0210 nano-technology - Abstract
The effect of interfacial fluorination on the structure, electronic properties, and performance of the HfO2/Al2O3 interface in charge-trapping memory (CTM) devices is investigated using the first-principles calculation. The impact of the interface states on the characteristics of traps in the HfO2 trapping layer at the HfO2/Al2O3 interface is studied first, and the results indicate that the interfacial states lead to performance degradation with respect to both reliability and the memory window of CTM devices during program/erase cycles. In the study of F passivation, F substitutions (FO) and F interstitials (Fi) tend to improve the thermal stability of the interface for higher interfacial F contents. Further, the FO-passivated interface is energetically more stable than the Fi-passivated interface. In addition, the FO-passivated interface can reduce the interface states that are partially (or completely) caused by breaking covalent interfacial bonds. Furthermore, a substantially improved HfO2/Al2O3 interface, with effective interfacial passivation in CTM devices, is obtained. Therefore, this study helps explain the intrinsic principle of interface passivation and opens new ways for performance improvement of the HfO2/Al2O3 interface in CTM devices.The effect of interfacial fluorination on the structure, electronic properties, and performance of the HfO2/Al2O3 interface in charge-trapping memory (CTM) devices is investigated using the first-principles calculation. The impact of the interface states on the characteristics of traps in the HfO2 trapping layer at the HfO2/Al2O3 interface is studied first, and the results indicate that the interfacial states lead to performance degradation with respect to both reliability and the memory window of CTM devices during program/erase cycles. In the study of F passivation, F substitutions (FO) and F interstitials (Fi) tend to improve the thermal stability of the interface for higher interfacial F contents. Further, the FO-passivated interface is energetically more stable than the Fi-passivated interface. In addition, the FO-passivated interface can reduce the interface states that are partially (or completely) caused by breaking covalent interfacial bonds. Furthermore, a substantially improved HfO2/Al2O3 inter...
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- 2019
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8. Growth and electrical properties of Na1/2Bi1/2TiO3-BaTiO3 lead-free single crystal with morphotropic phase boundary composition.
- Author
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Chao Chen, Xiangping Jiang, Yueming Li, Feifei Wang, Qinhui Zhang, and Haosu Luo
- Subjects
OXIDES ,CRYSTALS ,CRYSTALLOGRAPHY ,HYSTERESIS ,ELECTROMAGNETIC induction - Abstract
In present work, lead-free single crystal 0.94Na
1/2 Bi1/2 TiO3 -0.06BaTiO3 (NBBT94/6) with dimension of [uppercase_phi_synonym]40 mm×10 mm was grown by a precisely controlled top seeded solution growth method. The crystal structure measurement result indicates that the NBBT94/6 single crystal exhibits the feature of rhombohedral-tetragonal phase coexistence at room temperature. The crystallographic orientation dependence of electrical properties for NBBT94/6 single crystal was investigated in detail. The remnant polarizations (Pr ) of <001>, <001>, and <111> oriented crystals are 16.02 μC/cm2 , 22.16 μC/cm2 , and 27.23 μC/cm2 , respectively. The corresponding coercive fields (Ec ) are 24.89, 20.72, and 15.36 kV/cm. Moreover, a double hysteresis loop appears at the depolarization temperature. High piezoelectric properties d33 of 360 pC/N and kt of 62% were obtained in the <001> oriented crystals due to the engineered domain configuration which make them promising candidates for environmental friendly solid-state actuator applications. [ABSTRACT FROM AUTHOR]- Published
- 2010
- Full Text
- View/download PDF
9. Radial vibration mode of 0.71Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 single crystal and its applications.
- Author
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Feifei Wang, Dan Zhou, Laihui Luo, Xiangyong Zhao, Haosu Luo, Yuanwei Zhang, Jun Wu, and Hua Zhu
- Subjects
- *
FERROELECTRICITY , *CRYSTALS , *LEAD compounds , *PIEZOELECTRIC devices , *FINITE element method - Abstract
Ferroelectric single crystal (1-x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMNT) has attracted considerable attention for its outstanding piezoelectric properties after poled along the <001> or <101> directions and it is being actively applied to various ultrasonic devices. However, almost all previous applications focus on the longitudinal extension, transverse extension, thickness extension and thickness shear vibration mode. Here, we investigated the radial vibration mode of the <001> poled 0.71Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 single crystal. Both the finite element simulation and experimental results have shown that the performance of radial vibration mode is excellent. The coupling coefficient of radial vibration mode can reach 0.84 and the anisotropy of the circular plate is very weak after it was poled along the <001> direction. Based on this mode, we further designed and fabricated a disk-type piezoelectric transformer and the open circuit voltage step-up ratio reached about 50 with no spurious vibration mode around the resonance frequency. All these have shown that the radial vibration mode of PMNT single crystal is also promising and useful for other piezoelectric device applications. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
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10. Electric-field control of electronic transport properties and enhanced magnetoresistance in La0.7Sr0.3MnO3/0.5BaZr0.2Ti0.8O3-0.5Ba0.7Ca0.3TiO3 lead-free multiferroic structures
- Author
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Feifei Wang, Yu-Kuai Liu, Guanyin Gao, Ren-Kui Zheng, and Jian-Min Yan
- Subjects
010302 applied physics ,Materials science ,Condensed matter physics ,Magnetoresistance ,General Physics and Astronomy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Piezoelectricity ,Nuclear magnetic resonance ,Ferromagnetism ,Electrical resistivity and conductivity ,Electric field ,0103 physical sciences ,Grain boundary ,Charge carrier ,Multiferroics ,0210 nano-technology - Abstract
We report the fabrication of lead-free multiferroic structures by depositing ferromagnetic La0.7Sr0.3MnO3 (LSMO) polycrystalline films on polished 0.5BaZr0.2Ti0.8O3-0.5Ba0.7Ca0.3TiO3 (BZT-BCT) piezoelectric ceramic substrates. By applying electric fields to the BZT-BCT along the thickness direction, the resistivity of LSMO films can be effectively manipulated via the piezoelectric strain of the BZT-BCT. Moreover, the LSMO polycrystalline films exhibit almost temperature independent and significantly enhanced magnetoresistance (MR) below TC. At T = 2 K and H = 8 T, the MR of polycrystalline films is approximately two orders of magnitude higher than that of LSMO epitaxial films grown on (LaAlO3)0.3(SrAl1/2Ta1/2O3)0.7 single-crystal substrates. The enhanced MR mainly results from the spin-polarized tunneling of charge carriers across grain boundaries. The LSMO/BZT-BCT structures with electric-field controllable modulation of resistivity and enhanced MR effect may have potential applications in low-energy consumption and environmentally friendly electronic devices.
- Published
- 2017
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11. Composition induced structure evolution and large strain response in ternary Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3-SrTiO3 solid solution
- Author
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Feifei Wang, Chung Ming Leung, Tao Wang, Wangzhou Shi, and Yanxue Tang
- Subjects
Crystallography ,Materials science ,Piezoresponse force microscopy ,General Physics and Astronomy ,Thermodynamics ,Dielectric ,Ternary operation ,Piezoelectricity ,Ferroelectricity ,Perovskite (structure) ,Phase diagram ,Solid solution - Abstract
A ternary perovskite lead-free solid solution Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3-SrTiO3 was designed and fabricated using a conventional fabrication process. The temperature and composition dependence of the ferroelectric, dielectric, piezoelectric, and electromechanical properties were systematically investigated, and a schematic phase diagram was established. The introduction of the SrTiO3 was found to induce a structure evolution from the ferroelectric rhombohedra to ergodic relaxor pseudocubic phases. At a critical composition with SrTiO3 of 0.15, large strain level of ∼0.25% was obtained under a moderate field of 4.4 kV/mm at 0.1 Hz and the normalized strain reached up to 585 pm/V. Through the combination of the X-ray diffraction results with the piezoresponse force microscopy analysis, the composition induced structure evolution process and intrinsic mechanism responsible for the large strain response were discussed. The large strain level also makes the system quite promising for application to “on-off” actuators.
- Published
- 2013
- Full Text
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12. Large electrostrictive effect in ternary Bi0.5Na0.5TiO3-based solid solutions
- Author
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Qirong Yao, Wangzhou Shi, Chengchao Jin, and Feifei Wang
- Subjects
Phase boundary ,Materials science ,Electrostriction ,Electric field ,Ferroelectric ceramics ,Analytical chemistry ,General Physics and Astronomy ,Mineralogy ,Ternary operation ,Ferroelectricity ,Piezoelectricity ,Solid solution - Abstract
In the present work, a ternary solid solution (0.935-x)Bi0.5Na0.5TiO3-0.065BaTiO3-xSrTiO3 (BNBST, BNBSTx) was designed and fabricated using the traditional solid state reaction method. A morphotropic phase boundary between the ferroelectric long-range-order and relaxor pseudocubic phases was determined around x of 0.22 for poled solid solutions. The further increase of SrTiO3 substitution turned the depolarization temperature Td to below ambient temperature and led to a sharp decrease in the remnant polarization Pr and quasi-static piezoelectric constant d33. A large electrostrictive coefficient Q of 0.026 m4 C−2 was obtained for BNBST0.30, which was entirely comparable to the well-known electrostrictive material Pb(Mg1/3Nb2/3)O3, recently reported Bi0.5Na0.5TiO3-BaTiO3-K0.5Na0.5NbO3, and Bi0.5Na0.5TiO3-BaTiO3-KNbO3. Under a moderate electric field of 4 kV/mm, the electrostrictive strain can reach as high as ∼0.11%. Furthermore, the electric-field-induced strain exhibited weak temperature-dependent behavi...
- Published
- 2013
- Full Text
- View/download PDF
13. The influence of charged ions on the electro-optical properties of polymer-dispersed liquid crystal films prepared by ultraviolet-initiated cationic polymerization
- Author
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Fang Liu, Chaoyong Yang, Lilong Yu, Hui Cao, Ping Song, Aijun Jiao, Cuihong Zhang, Huai Yang, and Feifei Wang
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chemistry.chemical_classification ,Materials science ,Dopant ,Cationic polymerization ,General Physics and Astronomy ,Ionic bonding ,Polymer ,Polymerization ,Chemical engineering ,chemistry ,Liquid crystal ,Electric field ,Organic chemistry ,Molecule - Abstract
Polymer-dispersed liquid crystal (PDLC) films based on epoxy resins were prepared by UV-initiated cationic polymerization using UVI-6974 as UV-initiator. The charged ions arose from photolysis of the UV-initiator remained in the liquid crystal (LC) droplet of the polymer matrix. Optical devices based on PDLC films derive their functional properties from the electric field induced reorientation of LC droplets. These PDLC films doped with ions showed different reorientation of LC molecules and electro-optical properties than those prepared without ionic dopants. When an electric field was applied across these PDLC films, the charged ions in the LC droplet migrated along the direction of the electric field in inducement of the electric field and assembled at the LC droplet/polymer interface. According to the situation mentioned above, the model of charged double layers at the LC droplet/polymer interface was set up in our study. The behavior was attributed to the charged double layers that cancel the field s...
- Published
- 2012
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14. Dual-resonance converse magnetoelectric and voltage step-up effects in laminated composite of long-type 0.71Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 piezoelectric single-crystal transformer and Tb0.3Dy0.7Fe1.92 magnetostrictive alloy bars
- Author
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Siu Wing Or, Chung Ming Leung, Feifei Wang, and Siu Lau Ho
- Subjects
Magnetization ,Materials science ,law ,Composite number ,Converse ,Magnetoelectric effect ,General Physics and Astronomy ,Magnetostriction ,Composite material ,Transformer ,Piezoelectricity ,Voltage ,law.invention - Abstract
We report a dual-resonance converse magnetoelectric effect and a dual-resonance voltage step-up effect in a laminated composite made by sandwiching the output (or secondary) section of a long-type 0.71Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 (PMN–PT) piezoelectric single-crystal transformer having a longitudinal-longitudinal polarization between two Tb0.3Dy0.7Fe1.92 (Terfenol-D) magnetostrictive alloy bars having a longitudinal magnetization. The reported converse magnetoelectric effect originates from the mechanically mediated resonance converse piezoelectric effect in the PMN–PT transformer and resonance converse magnetostrictive effect in the Terfenol-D bars. The additional voltage step-up effect results from the mechanically mediated resonance converse and direct piezoelectric effects in the PMN–PT transformer. The composite shows two sharp resonance peaks of 0.39 and 0.54 G/V in converse magnetoelectric coefficient (αB = dB/dVin) and of 1.4 and 2.1 in voltage step-up ratio (Vout/Vin) at about 54 and 120 kHz, corr...
- Published
- 2011
- Full Text
- View/download PDF
15. Growth and electrical properties of Na1/2Bi1/2TiO3–BaTiO3 lead-free single crystal with morphotropic phase boundary composition
- Author
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Feifei Wang, Xiang-Ping Jiang, Chao Chen, Yueming Li, Haosu Luo, and Qinhui Zhang
- Subjects
Phase boundary ,Crystallography ,Hysteresis ,Work (thermodynamics) ,Materials science ,Condensed matter physics ,Phase (matter) ,General Physics and Astronomy ,Crystal structure ,Composition (combinatorics) ,Piezoelectricity ,Single crystal - Abstract
In present work, lead-free single crystal 0.94Na1/2Bi1/2TiO3–0.06BaTiO3 (NBBT94/6) with dimension of Φ40 mm×10 mm was grown by a precisely controlled top seeded solution growth method. The crystal structure measurement result indicates that the NBBT94/6 single crystal exhibits the feature of rhombohedral-tetragonal phase coexistence at room temperature. The crystallographic orientation dependence of electrical properties for NBBT94/6 single crystal was investigated in detail. The remnant polarizations (Pr) of ⟨001⟩, ⟨001⟩, and ⟨111⟩ oriented crystals are 16.02 μC/cm2, 22.16 μC/cm2, and 27.23 μC/cm2, respectively. The corresponding coercive fields (Ec) are 24.89, 20.72, and 15.36 kV/cm. Moreover, a double hysteresis loop appears at the depolarization temperature. High piezoelectric properties d33 of 360 pC/N and kt of 62% were obtained in the ⟨001⟩ oriented crystals due to the engineered domain configuration which make them promising candidates for environmental friendly solid-state actuator applications.
- Published
- 2010
- Full Text
- View/download PDF
16. Radial vibration mode of 0.71Pb(Mg1∕3Nb2∕3)O3–0.29PbTiO3 single crystal and its applications
- Author
-
Yuanwei Zhang, Feifei Wang, Haosu Luo, Xiangyong Zhao, Dan Zhou, Jun Wu, Laihui Luo, and Hua Zhu
- Subjects
Vibration ,Transverse plane ,Materials science ,Condensed matter physics ,Molecular vibration ,General Physics and Astronomy ,Anisotropy ,Single crystal ,Ferroelectricity ,Piezoelectricity ,Coupling coefficient of resonators - Abstract
Ferroelectric single crystal (1−x)Pb(Mg1∕3Nb2∕3)O3–xPbTiO3 (PMNT) has attracted considerable attention for its outstanding piezoelectric properties after poled along the ⟨001⟩ or ⟨101⟩ directions and it is being actively applied to various ultrasonic devices. However, almost all previous applications focus on the longitudinal extension, transverse extension, thickness extension and thickness shear vibration mode. Here, we investigated the radial vibration mode of the ⟨001⟩ poled 0.71Pb(Mg1∕3Nb2∕3)O3–0.29PbTiO3 single crystal. Both the finite element simulation and experimental results have shown that the performance of radial vibration mode is excellent. The coupling coefficient of radial vibration mode can reach 0.84 and the anisotropy of the circular plate is very weak after it was poled along the ⟨001⟩ direction. Based on this mode, we further designed and fabricated a disk-type piezoelectric transformer and the open circuit voltage step-up ratio reached about 50 with no spurious vibration mode around ...
- Published
- 2008
- Full Text
- View/download PDF
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