Ke-Pi Chen

Publications (6)5.23 Total impact

• Article: An Approach to Improve the Piezoelectric Property of (Bi0.5Na0.5)TiO3–(Bi0.5K0.5)TiO3–BaTiO3 Lead‐Free Ceramics

  Ye-Jing Dai, Xiao-Wen Zhang, Ke-Pi Chen
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  ABSTRACT: Lead-free piezoelectric ceramics of an a(Bi0.5Na0.5)TiO3–b(Bi0.5K0.5)TiO3–cBaTiO3 (BNBK) ternary system close to the composition of MPB have been widely investigated in recent decades. In this research, the MPB Linear Combination Rule (LCR) is introduced to explore the ternary system of lead-free piezoelectric ceramics for the first time, and the best properties of d33=220 pC/N, kp=0.31, kt=0.476, Td=157°C, and ɛr=1648 are obtained for a composition with a/b/c=85.25/10.995/3.755. It is suggested that BNBK with the composition (85.25/10.995/3.755) is a candidate material for lead-free applications. Moreover, the LCR of MPB is an effective method, applicable to lead-free ceramics to search for an optimal composition with excellent properties.
  International Journal of Applied Ceramic Technology 09/2009; 8(2):423 - 429. · 1.38 Impact Factor
• Article: Morphotropic phase boundary and electrical properties of K1−xNaxNbO3 lead-free ceramics

  Ye-Jing Dai, Xiao-Wen Zhang, Ke-Pi Chen
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  ABSTRACT: Lead-free K1−xNaxNbO3 ceramics with x = 0.48–0.54 were prepared by a conventional solid-state reaction method to investigate the influence of the K/Na ratio on phase structures and electrical properties. The results suggest that a typical morphotropic phase boundary exists at x = 0.52–0.525, separating the monoclinic and orthorhombic phases. The sample with the composition near x = 0.52 shows the maximum values of the piezoelectric constant (d33 = 160 pC/N) and the electromechanical coupling coefficient (kt = 47%). The results provide a helpful guidance to consider the optimal ratio of K to Na for designing and developing new (K,Na)NbO3-based ceramics.
  Applied Physics Letters 01/2009; 94(4):042905-042905-3. · 3.84 Impact Factor
• Source

  Available from: arxiv.org

  Article: Field-induced Domain Reorientation and Polarization Rotation of <110> Oriented Pb(Mg1/3Nb2/3)O3-PbTiO3 Single Crystals

  Ke-Pi Chen, Xiao-Wen Zhang, Fei Fang, Hao-Su Luo
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  ABSTRACT: Polarization hysteresis loops, x-ray diffraction (XRD) and temperature dependent dielectric constant under different electric fields for <110> oriented 0.7 Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 single crystals were measured. The field-induced phase transition and the process of depolarization were discussed. The results show that with the electric field increasing, the crystal form changes along via polar-axis reorientation and polarization rotation. However, the depolarization process is not just the reversal of the polarization process. It is noticed that just from the temperature dependent dielectric behavior is not enough to judge the processes of the E-field induced phase transition.
  07/2002;
• Article: Electric-field-induced phase transition of <001> oriented Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals

  Ke-Pi Chen, Xiao-Wen Zhang, Hao-Su Luo
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  ABSTRACT: <001> oriented 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 single crystals were poled under different electric fields, i.e. Epoling=4 kV/cm and Epoling=13 kV/cm. In addition to the temperature-dependent dielectric constant measurement, X-ray diffraction was also used to identify the poling-induced phase transitions. Results showed that the phase transition significantly depends on the poling intensity. A weaker field (Epoling=4 kV/cm) can overcome the effect of random internal field to perform the phase transition from rhombohedral ferroelectric state with short range ordering (microdomain) FESRO to rhombohedral ferroelectric state with long range ordering (macrodomain) FElRO. But the rhombohedral ferroelectric to tetragonal ferroelectric phase transition originating from <111> to <001> polarization rotation can only be induced by a stronger field (Epoling=13 kV/cm). The sample poled at Epoling=4 kV/cm showed higher piezoelectric constant, d33>1500 pC/N, than the sample poled at Epoling=13 kV/cm. Comment: 7 pages, 2 figures
  06/2002;
• Article: Synthesis of calcium copper titanate ceramics via the molten salts method

  Ke-pi Chen, Xiao-wen Zhang
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  ABSTRACT: CaCu3Ti4O12 has a giant dielectric constant of up to 104 at room temperature and has great potential for various technological applications. In this work, CaCu3Ti4O12 ceramic powder was synthesized by heating a stoichiometric amount of CaCO3, CuO and TiO2 in molten NaCl–KCl and Na2SO4–K2SO4, respectively. The synthesis temperature was decreased from 1000 °C (required by conventional solid-state reactions) to 750 °C for NaCl–KCl or to 850 °C for Na2SO4–K2SO4. The flux type has a larger influence on the phase compositions and morphology of the resultant powders than the synthesis temperature does. The dielectric constant of the resulting ceramics is more than 104 over the wide frequency range from 100 Hz to 100 kHz. The dielectric loss tangent of the resulting ceramics is lower than 0.2 in the frequency range from 100 Hz to 100 kHz. The dielectric behavior of both samples is similar to the results obtained for CaCu3Ti4O12 ceramics that were synthesized by the sol–gel method.
  Ceramics International.
• Article: Field-induced effect in the -oriented 0.70Pb(Mg1/3Nb2/3)O3–0.30PbTiO3 single crystals

  Ke-Pi Chen, Xiao-Wen Zhang, Xiang-Yong Zhao, Hao-Su Luo
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  ABSTRACT: Temperature-dependent dielectric constant, X-ray diffraction(XRD), thermally stimulated discharging current (TSDC) and polarization hysteresis loops for <111>-oriented 0.70Pb(Mg1/3Nb2/3)O3–0.30PbTiO3 crystals after poling under different fields were measured. Comparing with unpoled sample during heating, except that there is a transition from the state of normal ferroelectric rhombohedral (macro-domain) to the state of relaxor ferroelectric rhombohedral (micro-domain) for the poled samples, it was found that no other phase transition was induced by poling fields. XRD showed that after poling the piezoelectric elongation of the unit cell occurred along the polar direction. It was suggested that an extra peak in the T–ε curve of poled sample around 105 °C is not only caused by a macro–micro domain transition but also caused by the depolarization process of 180° and 71° domain switching simultaneously.
  Materials Letters. 60:1634-1639.