Intrinsic-strain-induced ferroelectric order and ultrafine nanodomains in SrTiO3.

Nano ferroelectrics holds the potential application promise in information storage, electro-mechanical transformation, and novel catalysts but encounters a huge challenge of size limitation and manufacture complexity on the creation of long-range ferroelectric ordering. Herein, as an incipient ferroelectric, nanosized SrTiO3 was indued with polarized ordering at room temperature from the nonpolar cubic structure, driven by the intrinsic three-dimensional (3D) tensile strain. The ferroelectric behavior can be confirmed by piezoelectric force microscopy and the ferroelectric TO1 soft mode was verified with the temperature stability to 500 K. Its structural origin comes from the off-center shift of Ti atom to oxygen octahedron and forms the ultrafine head-to-tail connected 90° nanodomains about 2 to 3 nm, resulting in an overall spontaneous polarization toward the short edges of nanoparticles. According to the density functional theory calculations and phase-field simulations, the 3D strain-related dipole displacement transformed from [001] to [111] and segmentation effect on the ferroelectric domain were further proved. The topological ferroelectric order induced by intrinsic 3D tensile strain shows a unique approach to get over the nanosized limitation in nanodevices and construct the strong strain-polarization coupling, paving the way for the design of high-performance and free-assembled ferroelectric devices.

Negative-Pressure-Induced Large Polarization in Nanosized PbTiO3.

Ferroelectric materials usually undergo decay with particle size decreasing into the nanoscale. At the critical value, the crystal structure undergoes a transition from the ferroelectric to paraelectric phase and the ferroelectricity vanishes. It is a big issue to sufficiently maintain strong ferroelectricity at the nanoscale. Herein, it is reported that synthesized 0D freestanding PbTiO3 nanoparticles (NPs) present negative pressure along the c axis (Δc/cbulk × 100% = -2.406), inducing large spontaneous polarization PS (71.2 µC cm-2 in 12 nm). Further local structural studies by atomic pair distribution functions and extended X-ray absorption fine structure indicate the structural evolution of nanosized PbTiO3 . High-angle annular dark-field STEM images reveal the existence of preponderant PbO-terminations on the surface of the PbTiO3 NPs. Ab initio calculation reveals the enhanced hybridization between Pb and O ions, which gives rise to the negative pressure and tensile stress to stabilize the high tetragonality and large polarization. The present work demonstrates an untraditional route to enhance the ferroelectricity and related properties in functional nanostructured materials, being of significance to nanodevices.