The effect of inter-granular constraints on the response of polycrystalline piezoelectric ceramics at the surface and in the bulk

Abstract

The electro-mechanical coupling mechanisms in polycrystalline ferroelectric materials, including a soft PbZrxTi1−xO3 (PZT) and lead-free 0.9375(Bi1/2Na1/2)TiO3-0.0625BaTiO3 (BNT-6.25BT), have been studied using a surface sensitive low-energy (12.4 keV) and bulk sensitive high-energy (73 keV) synchrotron X-ray diffraction with in situ electric fields. The results show that for tetragonal PZT at a maximum electric field of 2.8 kV/mm, the electric-field-induced lattice strain (ε111) is 20% higher at the surface than in the bulk, and non-180° ferroelectric domain texture (as indicated by the intensity ratio I002/I200) is 16% higher at the surface. In the case of BNT-6.25BT, which is pseudo-cubic up to fields of 2 kV/mm, lattice strains, ε111 and ε200, are 15% and 20% higher at the surface, while in the mixed tetragonal and rhombohedral phases at 5 kV/mm, the domain texture indicated by the intensity ratio, I111/I111¯ and I002/I200, are 12% and 10% higher at the surface than in the bulk, respectively. The observed difference in the strain contributions between the surface and bulk is suggested to result from the fact that surface grains are not constrained in three dimensions, and consequently, domain reorientation and lattice expansion in surface grains are promoted. It is suggested that the magnitude of property difference between the surface and bulk is higher for the PZT than for BNT-6.25BT due to the level of anisotropy in the strain mechanism. The comparison of the results from different methods demonstrates that the intergranular constraints have a significant influence on the electric-field-induced electro-mechanical responses in polycrystalline ferroelectrics. These results have implications for the design of higher performance polycrystalline piezoelectrics.

Residual stress and domain switching in freeze cast porous barium titanate

“…This observation indicates that the constraint of the surrounding polycrystalline matrix is effectively released by introducing high volumes of aligned pores, which is the main reason for the enhanced domain switching response with reduced intergranular stresses in the highly porous freeze cast sample. The porosity effects studied here are analogous to 'skin' effects studied in dense piezoceramics, whereby lattice expansion and domain reorientation has been observed at free surfaces compared to the bulk due to a reduction in intergranular constraints [53]. A proposed mechanism for the enhanced extrinsic contribution of the high porosity freeze cast barium titanate due to a reduction in intergranular clamping is shown in Figure 9, adapted from the model proposed by Hall et al [42].…”

Domain wall-grain boundary interactions in polycrystalline Pb(Zr0.7Ti0.3)O3 piezoceramics

“…It should be noted that PFM is a surface sensitive method. This is particularly important for bulk ferroelectric/ferroelastic materials, as their properties strongly depend on the mechanical boundary conditions, which vary from plane strain in the bulk to plane stress at the surface [74]. This problem can be overcome by the recent advances in three-dimensional X-ray diffraction microscopy [31], which enables spatially-resolved mapping of domains with sub-100 nm resolution within the bulk.…”

Self‐poling and electromechanical response of crystallographically textured PMN‐32PT prepared by templated grain growth

“…15,16 Intrinsic and domain switching strain can be observed using in-situ x-ray and neutron diffraction techniques, by shifts in peak positions, peak broadening, and changes in relative peak intensities. [17][18][19][20][21][22] While the field-induced microscopic structural changes in bulk ceramics and single crystals have been studied in the past, 18,21,23,24 the mechanism by which textured ferroelectrics achieve their enhanced piezoelectric response is yet to be thoroughly investigated.…”

“…Intrinsic effects and domain switching are known to dominate the strain response in conventional ferroelectrics such as lead zirconate titanate (PZT), 14 whereas in relaxor ferroelectrics a reversible phase transformation at higher fields can induce further strain 15,16 . Intrinsic and domain switching strain can be observed using in‐situ x‐ray and neutron diffraction techniques, by shifts in peak positions, peak broadening, and changes in relative peak intensities 17–22 . While the field‐induced microscopic structural changes in bulk ceramics and single crystals have been studied in the past, 18,21,23,24 the mechanism by which textured ferroelectrics achieve their enhanced piezoelectric response is yet to be thoroughly investigated.…”