A high energy synchrotron x-ray study of crystallographic texture and lattice strain in soft lead zirconate titanate ceramics

Abstract

The lattice parameters and crystallographic texture in La, Sr-doped soft lead zirconate titanate ceramics were examined using high-energy synchrotron x-ray diffraction. The preferred orientations in poled tetragonal and rhombohedral ceramics near the morphotropic phase boundary, caused by ferroelectric domain switching, were determined by monitoring the (002)∕(200) and (111)∕(111¯) intensity ratios, respectively. The lattice strains were also monitored using the {111} and {200} plane spacings in tetragonal and rhombohedral ceramics, respectively. The diffraction experiments were carried out in transmission, enabling the true “bulk” state to be characterized. It was observed that for the tetragonal phase both the lattice spacing d{111} and the intensity ratio R{200} varied linearly as a function of sin2Ψ,Ψ being the angle between the plane normal and the macroscopic polar axis. Similar observations were made for d{200} and R{111} in rhombohedral ceramics. The results are interpreted in terms of the remanent macroscopic strain state due to poling and the resulting relative misfit between any given grain and the surrounding matrix, which creates significant intergranular stresses. The tetragonal {111} and rhombohedral {200} plane spacings were identified as important monitors of intergranular stress, since the elongation of a grain along the tetragonal ⟨111⟩ or rhombohedral ⟨200⟩ directions, respectively (due to non-180° domain wall motion), is zero in the absence of the constraint imposed by neighboring grains. As a result, the tetragonal {111} or rhombohedral {200} reflections are sensitive only to the macrostrain of the polycrystal. It is proposed that the nonlinear and hysteretic piezoelectric response of the lattice strain reported in previous studies is primarily a result of coupling between the extrinsic non-180° ferroelectric domain switching mechanisms and the intrinsic lattice strain.

Revisiting the blocking force test on ferroelectric ceramics using high energy x-ray diffraction

“…However, poling the material also induces compressive residual stress along the poling direction. 5 These two effects seems to be balanced here, resulting in a very small variation of d 002 under electric field for w ¼ 0, and hence a very small e ð002Þ . For w ¼ 90 , little intrinsic piezoelectric effect is expected on d 002 , since the corresponding orientation is mostly loaded under shear piezoelectric mode.…”

“…A linear dependence of the strain as a function of cos 2 w is often assumed. 5 It is worth noting that this expected dependence is based on the assumption of no initial internal stresses and isotropic elasticity, 21 which is not guaranteed at all for piezoelectric ceramics. 14 …”

“…3,4 In recent years, diffraction techniques have been exploited as a means of evaluating the local lattice strain and domain switching behaviour of polycrystalline ferroelectric materials in response to external electric and/or mechanical loading. [3][4][5][6][7][8][9][10][11][12][13][14] These studies have shed new light on ferroelectric behaviour and enabled the origins of non-linearities to be characterised.…”

Domain Wall Displacement is the Origin of Superior Permittivity and Piezoelectricity in BaTiO3 at Intermediate Grain Sizes

“…A preferred domain texture evolves during electric field application as a fraction of the non-180° ferroelectric/ferroelastic domains reorient towards a more preferred direction relative to the applied field [23]. During this domain reorientation, crystallographic and microstructural effects as a result of electric-field-induced lattice strain and domain wall motion can be measured using X-ray and neutron diffraction [24][25][26][27][28][29][30][31]. Domain reorientation, specifically, can be quantified using the intensity interchange between the different orientation variants.…”

Strain Mechanisms in Lead-Free Ferroelectrics for Actuators

“…Therefore, the interdependent relationship between grain orientation and constraints, switching events, and intergranular stresses should determine the relative content of electric field induced phases. 144,452,453 BNT-based ceramics have been shown to feature either an electric field induced transformation into a single phase 142 or a phase mixture 141,143,145,146,434,454 depending on chemical composition. 430 Moreover, the electric field required to induce a phase transition and its completeness depends on crystallographic direction.…”