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Our early work showed that the evolution of the twin boundary pattern exhibits an avalanche behavior upon external loading of ferroelastic materials [Salje et al., Phys. Rev. B 83, 104109 (2011)]. The distribution of "jerks" (singularities of potential energy change) was found to follow a power law distribution below a Vogel–Fulcher temperature, mainly related to the movement of kinks in domain boundaries. We use molecular dynamics simulations to study the nucleation, scattering, and annihilation of phonons that are generated by the nucleation and propagation of such kinks. The interaction and scattering of phonons are correlated over a short time period and gradually become uncorrelated before annihilation at large temperature intervals. The movement and interaction of phonons show avalanche behavior. The probability of finding energy jerks follows a power law with exponents around 2.5–3. The distribution of waiting times between jerks also follows a power law. At temperatures above the Vogel–Fulcher temperature, scattering with thermal phonons becomes predominant and no phononic avalanches were observed. [ABSTRACT FROM AUTHOR]

Multiferroics often show significant elastic fluctuations even when the transition is strongly stepwise. Molecular dynamics simulations of a generic toy model show the appearance of tweed nanostructures (cross hatched patterns) in the paraelastic phase just above the transition point. This tweed lowers the elastic modulus C12 when approaching the transition temperature. The spatial and temporal correlations of the tweed structure follow the Vogel-Fulcher relationship, and the Vogel-Fulcher temperature is slightly below the transition temperature Ttrans, preventing this glassy state to freeze completely. Spatial correlations of shear strain show that the size of tweed patches reaches about eight lattice spacings near Ttrans. Cross- and rod-shaped diffuse scattering, similar to that in relaxors, emerges around {hh0}* and {h00}* Bragg reflections. The viscosity of the sample increases dramatically at the transition point with a significant precursor increase in the tweed regime. [ABSTRACT FROM AUTHOR]