Fan Chu

The Spontaneous Relaxor-Ferroelectric Transition of Pb(Sc0.5ta0.5)O3

A zero‐field spontaneous relaxor‐ferroelectric transition is reported in Pb(Sc0.5Ta0.5)O3 (PST). This behavior is different from that of other relaxors, where such transitions occur only under the field. A highly disordered PST that has the wide relaxation spectrum typical of relaxors is shown to transform spontaneously into a macroscopic ferroelectric state. Introduction of defects (lead vacancies) into the material impedes the transition resulting in the usual relaxor behavior. Dielectric properties of PST, with and without defects, are analyzed. For the interpretation of the observed properties, a model invoking an additional nonpolar phase is proposed. This model does not imply a freezing in the system. At the low‐frequency limit, it is possible to account for the Vogel–Fulcher (VF) law for the temperature of the maximum of the dielectric constant, using only the commonly accepted assumption of an exponentially wide relaxation time spectrum that shrinks on heating. The presented approach interprets th...

Spontaneous (zero‐field) relaxor–to–ferroelectric‐phase transition in disordered Pb(Sc1/2Nb1/2)O3

Recently, it has been shown that, upon cooling, disordered Pb(Sc1/2Ta1/2)O3 ceramics transform spontaneously from a relaxor state to a ferroelectric state when processed in a manner that suppresses lead vacancies. If lead vacancies are present, the spontaneous ferroelectric transition is suppressed and the ceramics exhibit the usual relaxor behavior in a wide temperature range. It is shown that disordered Pb(Sc1/2Nb1/2)O3 ceramics have a similar nature: When produced in a manner that does not eliminate lead vacancies, they exhibit normal relaxor behavior. However, if stoichiometry is tightly controlled, disordered Pb(Sc1/2Nb1/2)O3 transforms spontaneously (under zero‐bias field) from a relaxor into a normal ferroelectric upon cooling.

Investigation of relaxors that transform spontaneously into ferroelectrics

Abstract B-site disordered Pb(Sc½Ta½)O3 and Pb(Sc½Nb½)O3 can be prepared in a controlled manner to show (a) relaxor behavior and (b) relaxor that undergoes a first order ferroelectric phase transition at zero-bias field. The latter case is a first demonstration of a spontaneous transformation from relaxor to ferroelectric state. TEM, DSC and dielectric and electric characterization techniques are used to investigate this phase transformation and the results are reported. The spontaneous transformation is analyzed in light of existing relaxor models. It is found that cation-anion bond strength can be used as a criterion to predict materials with spontaneous relaxor-ferroelectric transformation.

Microstructure, structural defects, and piezoelectric response of Bi4Ti3O12 modified by Bi3TiNbO9

Microstructure, structural defects, and piezoelectric response of bismuth titanate (Bi4Ti3O12)1−x and bismuth titanium niobate (Bi3TiNbO9)x solid solution with x=0.05 and 0.2 were investigated. Depending on x and on the sintering temperature different microstructures and piezoelectric responses were observed. For a low content in Bi3TiNbO9 (x=0.05) and a high sintering temperature (1130 °C), a coarse grain size is present, the number of structural defects within the grain is small, and there is a strong dependence of d33 on the ac pressure. For higher Bi3TiNbO9 (x=0.2) content or for lower sintering temperature (1080 °C) and x=0.05, the grain size is finer and a large number of structural defects is present within the grains. In particular, for x=0.2, high resolution transmission electron microscopy shows a high concentration of intergrowth defects which consist of Bi3TiNbO9 layers inserted in the Bi4Ti3O12 matrix in a more or less random way. In these samples, there is a very small dependence of d33 on t...

Practical consequences of the extrinsic contributions to the properties of piezoelectric sensors and actuators

Extrinsic contributions to the piezoelectric properties of ferroelectric ceramic sensors and actuators are described. A new formalism which describes contributions of vibrating domain walls to the piezoelectric properties is presented. The formalism is based on the classical Rayleigh law and allows calculations of the piezoelectric coefficients as a function of amplitude and frequency of the driving field. The domain wall contributions to the piezoelectric properties of lead zirconate titanate (PZT), barium titanate (BaTiO/sub 3/) and high temperature bismuth titanate (Bi/sub 4/Ti/sub 3/O/sub 12/) based ceramics are discussed. The effects of microstructural parameters on the piezoelectric properties of ceramics are discussed in terms of domain wall vibrations. It is demonstrated how piezoelectric properties of ceramics may be tailored by manipulating domain wall contributions.