Texture and anisotropy of piezoelectric ceramics

Shan Wan, Purdue University

Abstract

Piezoelectricity in ceramics is determined by both single crystal properties and domain orientation distribution (DOD). In lead zirconate titanate (PZT) piezoelectric ceramics preferred domain orientations and related property anisotropies can be tailored using thermal treatment, mechanical poling and electric field poling. Thermal treatment cannot induce preferred orientation because temperature is not a vector or a tensor, but it can change the preferred orientation of textured PZT ceramics through thermal depoling. PZT ceramics also have ferroelastic properties, which can be shown using mechanical poling. Domain switching under electric field is the most effective way to control the orientation distribution of PZT materials. This is demonstrated by poling and cross-poling using applied electric fields. By cross-poling, the preferred domain orientation distribution and materials anisotropy can be strengthened. Domain orientation distributions in piezoelectric ceramics were characterized by conventional x-ray diffraction and synchrotron x-ray sources. The anisotropy of electric and mechanical properties was compared to domain orientation distributions. Elastic constants measured by the acoustic method and fracture toughness from Vickers indentation show the mechanical property anisotropy induced by poling. Results on piezoelectric constants and dielectric constants indicate that electrical property anisotropies are also changed by poling and the associated 90° domain switching. An orientation dependent model has been proposed to evaluate 90° domain switching in piezoelectric ceramics. The electric field induced domain switching fraction has been calculated and the corresponding preferred orientation distribution has been predicted based on this model. The domain switching critical energy, including internal strain energy and domain wall motion energy, has been treated as orientation dependent. This modeling gives an accurate prediction of texture in piezoelectric ceramics under electric field and the remnant texture after poling and cross-poling, when compared to experimentally measured pole figures.

Degree

Ph.D.

Advisors

Bowman, Purdue University.

Subject Area

Materials science

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