Fracture physics, a field of study in materials science, works on understanding how and why things break by quantifying and analyzing fracture surface topography. Scientists can reconstruct the history of a crack and determine the conditions that led to the initial formation of said crack. Preventing fractures is key in many industries such as aircraft, power plants, gas pipelines, and electronics. However, fracture formation is required in other industries such as rock quarries. Controlled cracking is receiving attention as a possible tool for device nanopatterning.
The recent article by Catalan Institute of Nanoscience and Nanotechnology “Flexoelectric Fracture-Ratchet Effect in Ferroelectrics” specifically reviews research regarding how cracks in ferroelectrics spread more easily in the polar direction. Ferroelectric materials are materials possessing a natural charge polarization, which can be reversed by an external electric field.
This research conducted by Kumara Cordero-Edwards et al. demonstrates that crack-generated flexoelectricity has the ability to increase or hinder crack propagation. Flexoelectricity is the property of certain materials that allows them to emit a small voltage when a non-uniform pressure is applied. This response is localized, reducing in strength as you move away from the point of greatest pressure. Whether crack propagation is increased or hindered depends on the polarization axis of the material.
Two key implications arise as a result of this study. The first is that cracks travelling in the polar direction are longer than those travelling against the polar direction. The second is that voltage can be used to manage crack propagation in polar materials due to the fact that the polarity of ferroelectric materials can be switched by voltage. This change in voltage would then allow for the crack propagation to be either increased or hindered, depending on the requirements of the individual situation.
Further information: Kumara Cordero-Edwards et al. Flexoelectric Fracture-Ratchet Effect in Ferroelectrics, Physical Review Letters (2019). DOI: 10.1103/PhysRevLett.122.135502