Evaluation of Phase and Domain Switching in Sn-Doped BCZT Piezoceramics with Coexisting Ferroelectric Phases

Large electrostrain properties are often observed in piezoelectric ceramics for conditions favoring a coexistence of multiple ferroelectric phases. However, the prevalence of different electric-field-induced microscopic mechanisms, viz. phase transition and domain switching, and their relative roles towards macroscopic electrostrain response are not readily understood. Here, we used in situ synchrotron X-ray diffraction and micromechanical modeling to self-consistently describe the electric-field-induced microscopic mechanisms in grains of different orientations in a polycrystalline Pb-free piezoceramic. We reveal, from experimental and modeling results, a unique tetragonal-to-orthorhombic-to-tetragonal phase transformation induced under low electric fields (< 1 kV/mm) in grains with 002 crystallographic poles oriented either within 20 degrees or orthogonal to the applied electric-field direction. In contrast, grains with their 002 poles oriented 30 degrees- 80 degrees to the electric-field direction undergo a continuous tetragonal-to-orthorhombic transformation for electric fields larger than 1 kV/mm. These results emphasize the critical role of a phase-transition-assisted domain switching mechanism in grains of specific orientations towards realizing a large electrostrain coefficient of d(33)* similar to 600 pm/V under low electric fields (< 1 kV/mm) in the Pb-free Sn-doped (Ba,Ca)(Zr,Ti)O-3 piezoceramic.