Nonlinear Dielectric and Piezoelectric Responses in (Bi,La)FeO 3 -Pb(Ti,Mn)O 3 Ceramics
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Nonlinear Dielectric and Piezoelectric Responses in (Bi,La)FeO3-Pb(Ti,Mn)O3 Ceramics Guiyang Shi, Shundong Bu, Rui Dai, Shengwen Yu and Jinrong Cheng School of Materials Science and Engineering, Shanghai University, Shanghai, 200072 ABSTRACT Polycrystalline solutions of 0.6(Bi0.9La0.1)FeO3-0.4Pb(Ti1-xMnx)O3 (BLF-PTM, x=0 and 0.01) have been fabricated by the so-gel process combined with a solid state reaction method. BLF-PTM exhibits the nonlinear dielectric and piezoelectric responses under applied fields. Rayleigh law has been used to evaluate the irreversible contribution of the domain walls movement to the nonlinear dielectric response. Rayleigh analysis reveals that a mechanism with no associated loss exists in the BLF-PTM of x=0.01. The real part piezoelectric coefficient of BLF-PTM linearly increases with increasing the electric fields. The dielectric and piezoelectric nonlinear coefficient of 0.17×10-3 m/V and 0.897 ×10-17 m2/V2 respectively are obtained for BLF-PTM of x=0.01, which are smaller than those of 0.22×10-3 m/V and 1.19 ×10-17 m2/V2 for BLF-PTM of x=0. Our results indicate that Mn doping increase the intrinsic piezoelectric properties of BLF-PTM reducing the extrinsic contributions to piezoelectric responses. INTRODUCTION Piezoelectric ceramics are usually subject to high applied fields of 15-20 kV/cm to obtain a high strain magnitude for actuator applications. [1] In such conditions, the behavior of piezoelectric ceramics can not be described by the linearly constitutive equations of piezoelectricity. The dielectric and piezoelectric responses exhibit the large nonlinearity with increasing electric fields, as result from the motion of domain wall [2-6]. The dielectric and piezoelectric nonlinearities have been extensively studied under the high electric fields and stresses. It is found that the dielectric permittivity and piezoelectric d33 coefficients obey the Rayleigh law within suitable field regions [3,6]. The Rayleigh relationships utilized to describe the dielectric and piezoelectric nonlinearity could be expressed by Eq. (1) and Eq. (2) [7]:
' int' i ' E0
(1)
d ' dint' i d' E0
(2)
where εinti′ and dinti′ are the initial dielectric and reversible piezoelectric responses at zero electric field, the αε′ and αd′ are the dielectric and piezoelectric Rayleigh coefficient, respectively. The Rayleigh approach also requires that the field-dependence of the dielectric permittivity and the hysteretic response of the material should obey the same relations [8]:
" " E0
4 ' E0 3
and W 0 E0 (3) "
Where αε′′ is the imaginary part of the relative dielectric permittivity, and W is the area of the P-E hysteresis loop or the consumed electrical loss energy. The Rayleigh coefficient reflects the mobility of domain wall under the external fields and thus the nonlinear electrical behavior of materials. It has been reported that hard PZT ceramics have aαε′ of 0.83×10-3 m/V smaller than that of 1.38×10-3 m/V for soft PZT [1,9], reflecting that the extrinsic contribution
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