We report the breakdown electric field and energy density of laser ablated BaTiO(3)/Ba((1-x))Sr(x)TiO(3) (x = 0.7) (BT/BST) relaxor-ferroelectric superlattices (SLs) grown on (100) MgO single crystal substrates. The dielectric constant shows a frequency dispersion below the dielectric maximum temperature (T(m)) with a merger above T(m) behaving similarly to relaxors. It also follows the basic criteria of relaxor ferroelectrics such as low dielectric loss over wide temperature and frequency, and 50 K shift in T(m) with change in probe frequency; the loss peaks follow a similar trend to the dielectric constant except that they increase with increase in frequency (~40 kHz), and satisfy the nonlinear Vogel-Fulcher relation. Well-saturated ferroelectric hysteresis and 50-80% dielectric saturation are observed under high electric field (~1.65 MV cm(-1)). The superlattices demonstrate an 'in-built' field in as grown samples at low probe frequency (<1 kHz), whereas it becomes more symmetric and centered with increase in the probe frequency system (>1 kHz) which rules out the effect of any space charge and interfacial polarization. The P-E loops show around 12.24 J cm(-3) energy density within the experimental limit, but extrapolation of this data suggests that the potential energy density could reach 46 J cm(-3). The current density versus applied electric field indicates an exceptionally high breakdown field (5.8-6.0 MV cm(-1)) and low current density (~10-25 mA cm(-2)) near the breakdown voltage. The current-voltage characteristics reveal that the space charge limited conduction mechanism prevails at very high voltage.
We report unipolar resistive switching suitable for nonvolatile memory applications in polycrystalline BiFeO 3 thin films in planar electrode configuration with nonoverlapping Set and Reset voltages, On/Off resistance ratio of ∼10 4 and good data retention (verified for up to 3,000 s). We have also observed photovoltaic response in both high and low resistance states, where the photocurrent density was about three orders of magnitude higher in the low resistance state as compared to the high resistance state at an illumination power density of ∼100 mW/cm 2 . Resistive switching mechanisms in both resistance states of the planar device can be explained by using the conduction filament (thermo-chemical) model. C
Single phase polycrystalline thin films (∼100 nm) of BaZr0.05(FexTi1−3x/4)0.95O3, with x = 0 (BZT) and 0.015 (BZFT15), were grown on Pt/TiO2/SiO2/Si substrate using pulsed laser deposition technique. Room temperature ferromagnetism with a remanent magnetization (Mr) ∼ 1.1 × 10−1 emu/cm3 and a coercive field (Hc) ∼ 0.1 kOe was observed in BZFT15 film. The ferroelectric domain switching in both BZT and BZFT15 films is confirmed by piezoresponse force microscopy (PFM). The magnetoelectric coupling coefficient (α) measured at room temperature in the BZFT15 film in in-plane magnetized-out of plane polarized configuration (L-T mode) was found to be ∼165 mV/cm Oe. It is argued that the observed ferromagnetism in BZFT15 films arises from the oxygen vacancy (Ov) mediated (Fe3+–Ov–Fe3+) exchange.
A B S T R A C THigh quality (1 0 0) oriented thin films of (Y 0.9 Bi 0.1 )(Fe 0.5 Cr 0.5 )O 3 [YBFCO] were deposited on (1 0 0) LAO substrates with conducting LNO buffer layer as bottom electrode. YBFCO thin film was found to demonstrate interesting room temperature multiferroic properties where the origin of weak ferroelectricity could be mainly attributed to disordered transition metal ions of unlike spins, and magnetic behavior was ascribed to uncompensated weak ferromagnetism arises due to magnetic cluster state in disordered system. Dielectric anomaly near magnetization reversal temperature (T irr ) revealed magnetodielectric effect in YBFCO film. In addition, leakage current behavior of the film was explained by trap-controlled space-charge-limited current conduction (SCLC) mechanism.
Recently, observation of switchable polarization-induced ferroelectric photovoltaic effect (FEPV) in BiFeO3 (BFO) has attracted great interest. In order to improve its FEPV properties, co-substituted [Bi0.9La0.1][Fe0.97Ta0.03]O3 (BLFTO) films were fabricated on Pt/TiO2/SiO2/Si substrates by pulsed laser deposition (PLD). The phase formation of the films was confirmed by X-ray diffraction, Raman spectroscopy, and XPS studies. The FEPV properties in La and Ta co-doped BiFeO3 (BFO) thin films were evaluated under illumination using sandwich configuration with a transparent conducting electrode (TCE) graphene as top electrode. The TCE electrode was transferred by chemical method on BLFTO thin films. The band gap of the films was determined to be 2.66 eV from spectrophotometric measurements, which is very close to that of pure BFO (2.7 eV). The ferroelectric nature of the films was characterized by P-E loop measurements, which indicated that leakage was still the prominent factor for not getting good polarization hysteresis. The piezo-force microscopy (PFM) studies however confirmed the ferroelectric nature of the films. The photovoltaic effect of the films was studied in both geometries, namely top-bottom and planar electrodes configurations. We will present aforementioned investigations and discuss possible photovoltaic applications of the above structure.
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