Size and temperature-dependent stability of polarization vortex in PbTiO3 nanosheet under uniaxial tension or compression

The stability of polarization vortex is absolutely crucial to the service performance of promising ferroelectric storage devices. Some phase field simulations were conducted on the PbTiO3 nanosheets with an initial polarization vortex under uniaxial tension or compression to investigate the conditions and types of vortex instability as well as the effects of the nanosheet size and temperature on them. The instability of polarization vortex has strong size and temperature dependence. The critical tensile stress decreases with increasing nanosheet size, and only the α-type vortex instability is observed in tensile nanosheets. However, the critical compressive stress first increases and then decreases with increasing nanosheet size, and there exists a peak size. The β-type (including β1 and β2-type) instability occurs when the nanosheet size is less than the peak size, but the α-type instability occurs when the nanosheet size is larger than the peak size. An elevated temperature reduces the critical tensile and compressive stresses, but increases the peak size. These are very important for design of promising nano-ferroelectric devices as high density memories.