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We investigated the influence of dislocations, located at the interface of a ferroelectric film and its underlying substrate, on the ferroelectric hysteresis loop including the remanent polarization and coercive field using phase-field simulations. We considered epitaxial ferroelectric BaTiO3 films and found that the hysteresis loop is strongly dependent on the type and density of interfacial dislocations. The dislocations that stabilize multiple ferroelectric variants and domains reduce the coercive field, and consequently, the corresponding remanent polarization also decreases. [ABSTRACT FROM AUTHOR]

The domain stability and domain structures of (001)-oriented PbTiO3 ferroelectric thin films subject to anisotropic in-plane strains were studied using phase-field method. Based on the simulation results, a room temperature domain/phase stability diagram was constructed for PbTiO3 thin films with the in-plane strains ranging from -5% to 5%. The predicted diagram is both quantitatively and qualitatively different from those obtained using thermodynamic calculations based on a single-domain assumption. [ABSTRACT FROM AUTHOR]

Ferroelectric SrBi2(Ta,Nb)2O9 (SBTN) thin films were deposited on Pt (200 nm)/TiOx (40 nm)/SiO2 (100 nm)/Si substrates by metal-organic decomposition. The effects of bombardment from accelerated argon and oxygen ions on the properties of SBTN thin films were investigated. It was found that the argon ion bombardment could decrease the crystallization temperature owing to the increase of internal energy of the films. Also, the oxygen vacancies at the interface between the SBTN film and platinum bottom electrode or at grain boundaries in the film were passivated through the oxygen ion treatment, resulting in the improved electrical properties. By optimizing the process parameters and using bombardment of accelerated argon and oxygen ions, SBTN films with good ferroelectric and electrical properties could be obtained, at a temperature as low as 650°C. [ABSTRACT FROM AUTHOR]

Strain relaxation behavior of (Pb,Sr)TiO3 thin films on (110) NdGaO3 substrates fabricated under different conditions have been investigated using high resolution x-ray diffraction. Dislocation densities and interfacial strain distribution have been systematically studied with samples in different postdeposition cooling rates. Strain relaxation and dislocation evolution are found to be dependent upon the cooling process. The relationship of dielectric properties and the strain and dislocations of the films were discussed. [ABSTRACT FROM AUTHOR]

Local polarization switching in epitaxial ferroelectric thin films in the presence of ferroelastic domain walls was studied using phase-field approach. The nucleation bias profile across a twin wall was analyzed, and the localization of preferential nucleation sites was established. This analysis was further extended to a realistic domain structure with multiple twin boundaries. It was observed that the local nucleation voltage required for a 180° domain switching is closely related to the number of such local defects. [ABSTRACT FROM AUTHOR]

Strain is generally known to increase the coercive field of a ferroelectric thin film as compared to a stress-free single crystal or a strain-relaxed film. We studied the coercive fields and remanent polarizations of (001)-oriented epitaxial barium titanate thin films using the phase-field approach. It is demonstrated, while the remanent polarization decreases as in-plane strain changes from being compressive to tensile, the variation of coercive field with strain is complicated. We noted more than two times drop in coercive field with a reduction of compressive strain of only ∼0.05%, which we attribute to the existence of multiple ferroelectric phases. [ABSTRACT FROM AUTHOR]

We studied the phase transitions, domain morphologies, and polarizations in BaTiO3/SrTiO3 superlattices grown on SrTiO3 substrates. Using the phase field approach, we discovered the remarkable influence of film/substrate interfacial coherency on the ferroelectricity of the SrTiO3 layers within a superlattice: it is an orthorhombic ferroelectric for an incoherent interface while it exhibits only induced polarization by the adjacent BaTiO3 layers for a coherent interface. We presented the domain morphologies within individual BaTiO3 and SrTiO3 layers which have different ferroelectric symmetries. The results are compared to ultraviolet Raman spectroscopy and variable temperature x-ray diffraction measurements. [ABSTRACT FROM AUTHOR]

Ferroelectric Bi3.25La0.75Ti3O12 (BLT) thin films were deposited on SrRuO3 (SRO) and Pt electrodes by pulsed laser deposition. The data retention characteristics of the BLT films on different electrode materials were characterized. The experimental results are well fitted by a stretched exponential decay model, indicating that BLT films on both Pt and SRO exhibit the similar decay mechanisms. However, the decay behavior is quite different due to the use of different bottom electrodes. The superior data retention performance of BLT film on conductive SRO electrode is believed to be from the reduction of domain polarization backswitching originated from the oxygen vacancies in the depletion region of BLT films. [ABSTRACT FROM AUTHOR]

Epitaxial c-axis-oriented Bi3.15Nd0.85Ti3O12 (BNT) thin films with thickness ranging from 150 to 350 nm were deposited on conductive SrRuO3 (SRO) on (001) SrTiO3 substrates by pulsed laser deposition. The top Pt electrode was deposited by sputtering to construct a capacitor Pt/BNT/SRO. The authors have evaluated the effective thickness (ti) and dielectric constant ([variant_greek_epsilon]i) of interfacial layers at the Pt/BNT and BNT/SRO interfaces based on the optical refractive index of the BNT layer and the capacitance frequency as well as the current-voltage characteristics of the capacitors. Using a series capacitor model, they have found that the dielectric constant of bulk BNT and the ti/[variant_greek_epsilon]i ratio are 586 and 1.46 nm, respectively. Knowing the optical dielectric constant ([variant_greek_epsilon]opt) and the product of [variant_greek_epsilon]optti of BNT thin films, the authors have estimated that the effective thickness and dielectric constant of the interfacial layers are 20.1 nm and 13.7, respectively. [ABSTRACT FROM AUTHOR]

Ferroelectric Bi3.25La0.75Ti3O12 (BLT) films were grown on Pt/Ti/SiO2/Si (Pt/Si), LaNiO3/Pt/Si, and LaNiO3/Si substrates using chemical solution deposition technique. X-ray diffraction analysis shows that films grown on conductive LaNiO3 electrodes had higher degree of (117) orientation as compared to that grown directly on Pt/Si substrate. High remanent polarization value (2Pr)∼43.14 μC/cm2 (Ec of 111 kV/cm) under an applied field of 396 kV/cm was obtained for BLT film on LaNiO3/Pt/Si as compared to a value of 26 μC/cm2 obtained for BLT film on Pt/Si directly. There was no degradation in the switchable polarization (Psw-Pns) after 1010 switching cycles. [ABSTRACT FROM AUTHOR]

An emerging area in condensed matter physics is the use of multilayered heterostructures to enhance ferroelectricity in complex oxides. Here we demonstrate that optically pumping carriers across the interface between thin films of a ferroelectric (FE) insulator and a ferromagnetic metal can significantly enhance the FE polarization. The photoinduced FE state remains stable at low temperatures for over one day. This occurs through screening of the internal electric field by the photoexcited carriers, leading to a larger, more stable polarization state that may be suitable for applications in areas such as data and energy storage. [ABSTRACT FROM AUTHOR]