Mechanisms of aging and fatigue in ferroelectrics

Phase-change actuator ceramics directly couple electrical and mechanical energies through an electric-field-induced phase transformation. These materials are promising for the replacement of the most common electro-mechanical ceramic, lead zirconate titanate, which has environmental concerns. Here, we show that by compositional modification, we reduce the grain-scale heterogeneity of the electro-mechanical response by 40%. In the materials investigated, this leads to an increase in the achievable electric-field-induced strain of the bulk ceramic of 45%. Compositions of (100–x)Bi0.5Na0.5TiO3–(x)BaTiO3, which initially possess a pseudo-cubic symmetry, can be tuned to undergo phase transformations to combined lower symmetry phases, thus decreasing the anisotropy of the transformation strain. Further, modelling of transformation strains of individual grains shows that minimum grain-scale strain heterogeneity can be achieved by precise control of the lattice distortions and orientation distributions of the induced phases. The current results can be used to guide the design of next generation high-strain electro-mechanical ceramic actuator materials.

mentioning

confidence: 64%

Maximising electro-mechanical response by minimising grain-scale strain heterogeneity in phase-change actuator ceramics

Oddershede¹,

Hossain

Daniels

2016

“…The lower intergranular stress, and the reduced variation in the behavior between the surface and bulk, will possibly lead to increased fracture toughness and improved fatigue lifetime. 30 In summary, the electro-mechanical coupling mechanisms in the polycrystalline PZT and lead-free BNT-6.25BT have been measured using a surface sensitive low-energy and bulk sensitive high-energy synchrotron XRD. Higher magnitudes of both lattice strain and non-180 domain switching are observed at the surface compared with the bulk for both materials.…”

mentioning

confidence: 99%

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

Hossain

Wang

Khansur

et al. 2016

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.

“…Several mechanisms, 19,20 like microcracking, 21,22 drift of charge carriers, 23,24 and structural changes, 25 have been reported to contribute to fatigue. This investigation is focused on structural changes caused by electric cycling, which leads to material degradation and thus fatigue.…”

mentioning

confidence: 99%

Cyclic electric field response of morphotropic Bi1/2Na1/2TiO3-BaTiO3 piezoceramics

Hinterstein

Schmitt

Hoelzel

et al. 2015