Ferroelastic domain dynamics: a multiscale study through in situ microscopy

This revealed divergent behaviours during the ramp down of said heat cycles. Pixel-by-pixel analysis, based on the collective propagation of domains known as avalanches, identified that the observable differences in behaviour was characteristic of an exponential mixing, a previously unreported phenomenon for ferroelastics.Subsequently, the sample size was reduced to explore scaling effects on the microscale, where the influence of the chemical environment was investigated; a dynamical treatment not previously explored in ferroelastics.

Several environments were tested, using an in situ Transmission Electron Microscopy (TEM) heating and gas, consisting of ultra-high vacuum (UHV), N2, O2/Ar, H2/N2/Ar. Dynamic analysis revealed the active suppression on domain patterning under the H2/N2/Ar environment. While the UHV, N2 and O2/Ar were comparable in terms of domain behaviours and to that of the bulk, the UHV was selected due to the experimental success rate.Building upon these findings, the thickness effect of specially designed freestanding samples was tested in the UHV environment via in situ heating TEM.

Experimental results correlated to the behavioural regimes known as the monopolar-crossover-dipolar regimes based on the interactions between kinks in the domain walls. Strain analysis from Scanning Procession Electron Diffraction (SPED) data was used correspondingly with Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) simulations to confirm the transition between these regimes and the behaviours therein.

Additionally, the foundation for automated measurements, using machine learning, was established to aid the measurement of domains’ characteristic such as the domain wall density and curvature.