Unusual Soft Mode Dynamics in Ferroelectric PbTiO3 Nanowire under Different Mechanical Boundary Conditions

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First-principles-based atomistic simulations are used to investigate equilibrium phases and soft mode dynamics in ultrathin ferroelectric PbTiO3 nanowire with poor surface charge compensation subjected to a wide range of mechanical boundary conditions. The presence of the depolarizing field along the nanowire's transverse directions leads to the appearance of a unique high-frequency hard phonon mode that can be used to characterize electrical boundary conditions. This mode is insensitive to the mechanical load. Hydrostatic pressure was found to significantly influence the Curie point and ferroelectric soft modes in the nanowire. Uniaxial stress applied either along axial or transverse nanowire's direction is capable of inducing polydomain flux-closure phases that have a unique “dynamical” fingerprint. In such phases, the modes that originate from the soft modes of bulk PbTiO3 become hard, which could open a way to potential identification of such nanodomain phases. In all cases, uniaxial stress significantly increases the Curie temperature.

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Journal of Applied Physics, v. 122, issue 21, art. 214103