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The flexoelectric effect can be exploited to control the polarization and domain structure in ferroelectric materials, potentially benefiting applications, such as nanoscale electromechanical systems, memory devices, and sensors. We report ferroelectric domain switching characteristics of PbTiO3(PTO) thin films induced by the flexoelectric effect. Epitaxially (001)-oriented PbTiO3(PTO) thin films were deposited on single-crystal Nb-doped SrTiO3substrates by pulsed laser deposition. Through the use of a piezoelectric force microscope and two surface electrodes, polarization domains were created vertically and horizontally within the PTO film. When subjected to a vertical external force, the domains with vertical orientation exhibited predictable switching behavior. Conversely, by imposing a vertical force during the scanning of domains oriented horizontally, we observed the formation of new domains with vertical orientation. However, in conditions where a vertical force was applied counter to the alignment of the horizontal domains, the anticipated switching of the vertical domains did not manifest. This study demonstrates that the flexoelectric effect can be harnessed to manipulate the switching of ferroelectric domains in PTO thin films using piezoresponse force microscopy.

We report the imprint effect on the energy storage performance of Bi-layered perovskite (Aurivillius) Bi3TaTiO9(BTTO) thin films. BTTO thin films were fabricated on single-crystal Nb-doped SrTiO3substrates using pulsed laser deposition, where the BTTO thin films showed epitaxial c-axis orientation crystal growth with square-shaped grains of terrace structures. The BTTO thin films exhibited ferroelectric hysteresis loops with a remnant polarization of several μC/cm2. An imprint phenomenon in the ferroelectric hysteresis loops occurred by applying the heat treatment of the BTTO thin film. By varying the annealing time (for 5 and 10 min at 550 °C in a vacuum of 10−5 Torr), we elucidated the imprint effect on the energy storage performance. We suggest that oxygen deficiencies induced by the heat treatment cause an imprint effect in the ferroelectric hysteresis loops. As a result, the imprint effect contributed to an increase in the stored energy density and a decrease in the energy loss density in the energy storage performance of the BTTO thin films. Our results demonstrate that the imprint effect can be a critical factor in achieving improved energy efficiency for energy storage performance, which provides new insights into the potential applications of energy storage devices with Bi-layered perovskite BTTO thin films.

We investigate the ferromagnetic properties of the conducting filament (CF) nanodots formed on epitaxial BiFeO3(BFO) thin film, which exhibit resistive switching behavior. 50-nm thick epitaxial BFO thin film was grown on Nb-doped SrTiO3single crystal substrates through pulsed laser deposition. The ferroelectric microcapacitor fabricated using the epitaxial BFO thin film shows excellent ferroelectric properties with a remanent polarization of approximately 32 μC/cm2and unipolar resistive switching behavior. CF nanodots with a diameter of approximately 16 nm are formed in the local region of the BFO thin film through conductive atomic force microscopy. Generally, ferromagnetic materials exhibit superparamagnetism, on a scale of tens of nanometers, as a result of the thermal energy of the magnetic moments. In this study, magnetic force microscopy demonstrates that the CF nanodot possesses ferromagnetism. It is suggested that exchange coupling between the CF nanodot and surrounding BFO causes the ferromagnetism of the nanodot. Our study provides new insight on the design of multistate memory cells with resistive switching and magnetic spin ordering, for application in high-density information storage media.