A Multiscale Study of Ferroelastic Domain Dynamics as a Function of Aspect Ratio

Akin to their sister ferroics (e.g ferroelectrics and ferromagnetics), ferroelastics are characterised by regions of differently orientated states (domains), separated by interfaces known as domain walls, that form when cooled below a critical temperature (T_C) in order to reduce its inherent free energy. Domain walls are of particular interest, exhibiting unique properties on the nanoscale from the bulk such as super-conductivity in an insulating medium¹. When an external field is applied, domains can further nucleate, annihilate or become mobile in response to the stimuli, presenting unique possibilities for active-adaptable devices².<br/>Temperature and stress are examples of such stimuli which are capable of switching the domain structure, a mechanism that mediates many of the functional properties utilised in applications such as memory devices³, switches and sensors. The understanding of how domains behave in response to externally applied fields is critical to the development of advanced applications such as neuromorphic computing⁴; based on the jerky mobility of DWs, and by extension domains, in materials with ferroelastic components⁵. These discrete jerks emit elastic fields that can destabilise surrounding structures and trigger a cascade of switching events known as avalanches, which can be utilised in conjunction with mean-field theory to characterise the overall behaviour of these dynamics⁶ which is an element of this investigation.<br/>Within this study, we complement work achieved on manipulating bulk behaviours⁶ and investigate ferroelastic domain dynamics at the microscale via <i>in situ</i> transmission electron microscopy (TEM) techniques. Varying the sample aspect ratios of free standing LaAlO₃ (LAO) lamella, samples were heat cycled <i>in situ</i> from room temperature, beyond T_C and back. We touch upon the effects of etched patterns within this context and explore the different domain behaviour with theoretical models. Finally, we correlate these results to the effects observed in free-standing BaTiO₃ lamella, to compare ferroelastic and ferroelectric systems. The results here presented highlight the inherent differences not only in domain dynamics as a function of the aspect ratio, but between different size scales, which are not comparable when mechanisms such as surface effects are considered on the microscale. Knowledge of the domain dynamics in bulk and towards micro-objects, is fundamental for the advancement of active adaptable and substrate free devices.<br/> <br/>¹ G. Catalan, J. Seidel, R. Ramesh, and J. F. Scott, Reviews of Modern Physics <b>84</b> (1), 119 (2012).<br/>² Dennis Meier, Nagarajan Valanoor, Qi Zhang, and Donghwa Lee, Journal of Applied Physics <b>129</b> (23), 230401 (2021).<br/>³ Ekhard K. H. Salje, Journal of Applied Physics <b>128</b> (16), 164104 (2020).<br/>⁴ Ekhard K. H. Salje, APL Materials <b>9</b> (1), 010903 (2021).<br/>⁵ Blai Casals, Guillaume F. Nataf, and Ekhard K. H. Salje, Nature Communications <b>12</b> (1) (2021).<br/>⁶ John J. R. Scott, Blai Casals, King-Fa Luo, Atta Haq, Davide Mariotti, Ekhard K. H. Salje, and Miryam Arredondo, Scientific Reports <b>12</b> (1) (2022).