Partial charge compensation in ferroelectric nanostructures is known to play a critical role in stabilizing equilibrium domain patterns. We use first-principles-based simulations to study the effect of partial charge compensation on the response of polarization to the electric field in PbTiO3 and BaTiO3 ultrathin films. Computational data predict that the response can be altered at the qualitative level by tailoring partial charge compensation. We report an unusual transition from ferroelectric to antiferroelectric to dielectric behavior induced by the change in the amount of compensating charge. Interestingly, films with antiferroelectric features exhibit superior potential for energy storage applications.
Molecular dynamics simulations are used to study the interaction of ferroelectric nanowires with terahertz (THz) Gaussian-shaped pulses of electric field. The computational data indicate the existence of two interaction scenarios that are associated with 'lossless' and dissipative, or 'lossy', interaction mechanisms. A thermodynamical approach is used to analyze the computational data for a wide range of THz pulses. The analysis establishes the foundation for understanding the nanowires' response to the THz pulses and reveals the potential of ferroelectric nanowires to function as nanoscale sensors of THz radiation. Various aspects of this THz nanosensing are analyzed and discussed.
Polarization reversal in ferroelectrics has been a subject of intense interest for many years owing to both its scientific appeal and practical utility. In the recent years the interest has increased even further thanks to the expectations of achieving ultrafast polarization reversal at the nanoscale. While most of the studies up to now are focused on the polarization reversal in ferroelectric thin films, we report the intrinsic dynamics of ultrafast polarization reversal in ferroelectric nanowires. Using atomistic first-principles-based simulations, we trace the time evolution of polarization under applied electric field to reveal the existence of two competing polarization reversal mechanisms: (i) domain-driven and (ii) homogeneous. The analysis of their microscopic origin allows us to postulate the associated laws and leads to a deeper understanding of polarization reversal dynamics in general. In addition, we find that in defect-free nanowires the polarization reversal can occur within picoseconds which potentially is very promising for ultrafast memory and other applications.
The role of different mechanical boundary conditions in the soft mode dynamics of ferroelectric PbTiO3 is systematically investigated using first-principles-based simulations and analytical model. The change in the soft mode dynamics due to hydrostatic pressure, uniaxial and biaxial stresses and biaxial strains is studied in a wide temperature range. Our computations predict: (i) the existence of Curie-Weiss laws that relate the soft mode frequency to the stress or strain; (ii) a non-trivial temperature evolution of the associated Curie-Weiss constants; (iii) a qualitative difference between the soft mode response to stresses/strains and hydrostatic pressure. The latter finding implies that the Curie-Weiss pressure law commonly used for residual stress estimation may not apply for the cases of uniaxial and biaxial stresses and strains. On the other hand, our systematic study offers a way to eliminate this difficulty through the establishment of Curie-Weiss stress and strain laws. Implications of our predictions for some available experimental data are discussed.
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