AVS 64th International Symposium & Exhibition
    Sustainability Focus Topic Wednesday Sessions
       Session SU+AS+EM+MS-WeM

Invited Paper SU+AS+EM+MS-WeM5
Toward a Greener World: The (Re)search for Lead-Free Piezoelectrics

Wednesday, November 1, 2017, 9:20 am, Room 5 & 6

Session: Piezoelectrics, Thermoelectrics, and Superconductors
Presenter: Xiaoli Tan, Iowa State University
Correspondent: Click to Email
Piezoelectricity refers to the linear coupling, in the direct effect, between mechanical stress and electric displacement, and in the converse effect, between mechanical strain and applied electric field. The proportionality constants are the piezoelectric coefficients which are equivalent between the direct and the converse effects. For the past six decades ceramics based on Pb(Zr1-xTix)O3 (PZT) perovskite oxides have been the workhorse of piezoelectric technology due to their excellent properties, ease of processing, and low cost. The high piezoelectric performance of PZT is primarily resulted from the intrinsic lattice distortion and the ferroelectric domain switching. However, environmental concerns with lead have stimulated worldwide intensive efforts in the search for lead-free piezoelectric ceramics.

The research efforts on lead-free piezoelectric ceramics have been largely concentrated on three solid solution families: BaTiO3-based, (K0.5Na0.5)NbO3-based, and (Bi1/2Na1/2)TiO3-based compositions. BaTiO3-based ceramics exhibit excellent piezoelectric coefficients, but their applications are limited by their low Curie points (~100 oC). (K0.5Na0.5)NbO3-based compositions possess high piezoelectric coefficients and relatively high Curie points (> 200 oC), but have stringent requirements on the processing conditions. (Bi1/2Na1/2)TiO3-based polycrystalline ceramics develop giant electrostrains (up to 0.70%), but usually require a very high electric field.

In this presentation, an overview of the recent development in the search and research on lead-free piezoelectric ceramics will be given. Their chemical compositions, structure evolutions, and mechanisms for property optimization will be discussed. In addition, two specific investigations will be presented. The first one is on the microstructural response to poling electric fields in the (Bi1/2Na1/2)TiO3–BaTiO3 solid solution. With the in situ transmission electron microscopy technique, it is directly observed that poling fields can either destroy or create morphotropic phase boundaries and the associated strong piezoelectric property. The second investigation is on the development of a giant electrostrain of 0.70% at 50 kV/cm at room temperature in {[Bi1/2(Na0.84K0.16)1/2]0.96Sr0.04}(Ti0.975Nb0.025)O3. This polycrystalline ceramic with randomly oriented grains is even better than some single crystals in terms of some electromechanical properties. In situ transmission electron microscopy examination indicates that the giant electrostrain is originated from the reversible phase transitions under applied electric fields.

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