Abstract
The evaluation of the piezoelectric properties of ferroelectric ceramics generally has a high level of uncertainty, due to incomplete poling, porosity, domain wall clamping and other effects. In addition, the poling process is often difficult and dangerous, due to the risk of breaking or damaging the sample. A method is described for the evaluation of the potential intrinsic piezoelectric response that a ceramic would have after full poling, without poling it. The method relies on the fact that any material undergoes an elastic softening below the ferroelectric transition temperature, whose magnitude can be expressed in terms of the intrinsic piezoelectric and dielectric coefficients of the material. Such a softening is equivalent to an electromechanical coupling factor averaged over all the components, due to the unpoled state of the sample, and can be deduced from a single temperature scan of an elastic modulus of a ceramic sample, spanning the ferroelectric and paraelectric states. The strengths, limits and possible applications of the method are discussed.
Highlights
Measuring the piezoelectric coefficients of ferroelectric (FE) ceramics is often afflicted by great uncertainty and may be a difficult task
It should be added that the coercive field is not necessarily well defined, since it depends on the degree of pinning of the domain walls from defects, which in turn may depend on the thermal and electrical history of the sample
The paraelectric to ferroelectric transition, a material undergoes an elastic softening of piezoelectric origin
Summary
Measuring the piezoelectric coefficients of ferroelectric (FE) ceramics is often afflicted by great uncertainty and may be a difficult task. The variability in the measured values of the effective piezoelectric constants dij∗ of nominally identical materials may be quite large. There are other factors determining the measured dij∗ , and a major difficulty is obtaining complete poling of the ferroelectric domains, with the spontaneous polarization Ps as parallel as possible to the applied field. Incomplete poling is common [3], and affects the measured values of the effective piezoelectric coefficients, which are proportional to the macroscopic polarization. Poling is only partial if the local field felt by each domain is lower than the coercive field necessary to move the domain walls and switch the polarization. It should be added that the coercive field is not necessarily well defined, since it depends on the degree of pinning of the domain walls from defects, which in turn may depend on the thermal and electrical history of the sample
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