Understanding how temperature affects the electronic transitions of BFO is important for design of BiFeO3 (BFO)-based temperature-sensitive device. Hitherto, however, there have been only very limited reports of the quantitative simulation. Here, we used density functional theory (DFT) and two-dimensional correlation analysis (2D-CA) techniques to calculate the systematic variations in electronic transitions of BFO crystal, over a range of temperature (50 similar to 1500 K). The results suggest that the heat accumulation accelerates the O-2p(4) orbital splitting, inducing the Fe3+-3d(5) -> Fe2+-3d(5)d(0) charge disproportionation. The origin is observed as the temperature-dependent electron transfer process changes from threefold degeneracy to twofold degeneracy. Additionally, the crystallographic orientation (111) can be used to control the 2p-hole-induced electronic transition as O -> unoccupied Fe3+-3d(5), in comparison to the O -> Bi-6p(3)+ Fe3+-3d(5)d(0) on the orientations (001) and (101). This study offers new perspective on the improvement of BFO-based temperature-sensitive device.

Densed BiFeO3(BFO) ceramics were sintered by using soft chemical derived fine powders. The microstructures, polarization and dielectric properties were investigated by means of X-rays diffraction (XRD), Scanning electron microscope (SEM), ferroelectric test system and impedance analyzer. The XRD patterns indicate that BFO ceramics with a single distorted perovskite structure are formed and no secondary phase appears in the ceramics. Through the dielectric response investigated over a wide range of temperature and frequency, it is found that the BFO ceramic sintered at 800 degrees C exhibited high dielectric permittivity and two dielectric relaxations. The remanent polarization and maximum polarizations were 0.232 and 0.443C/cm(2), respectively (at 25kV/cm).

Composite electrodes based on several ceramic oxides were tested for their chemical compatibility and electrochemical performance in systems based on composite Gd-doped ceria + alkaline carbonate electrolytes. Reactivity tests performed at 700 degrees C (accelerated testing conditions), involving the ceramic electrode materials and one mixture of Na and Li carbonates, identified two promising perovskyte-type ceramics, LaCoO3 and La0.8Sr0.2Co0.2Fe0.8O3, as the most stable. Co-pressed and co-sintered cell assemblies (electrode/electrolyte/electrode) involving composite electrodes (perovskytes mixed with alkaline carbonates)were studied in detail by scanning electron microscopy and tested by impedance spectroscopy in air in the temperature range 300-600 degrees C. These tests showed the potential of these composite electrodes for intermediate temperature applications, clearly surpassing in performance standard Au electrodes, here used as reference. (c) 2012 Elsevier Ltd. All rights reserved.

Lead zirconate titanate Pb(Zr0.50Ti0.50)O-3 (PZT) thin films were deposited by a polymeric chemical method on Pt(111)/Ti/SiO2/Si substrates to understand the mechanisms of phase transformations and the effect of film thickness on the structure, dielectric, and piezoelectric properties in these films. PZT films pyrolyzed at temperatures higher than 350 degrees C present a coexistence of pyrochlore and perovskite phases, while only perovskite phase grows in films pyrolyzed at temperatures lower than 300 degrees C. For pyrochlore-free PZT thin films, a small (100)-orientation tendency near the film-substrate interface was observed. Finally, we demonstrate the existence of a self-polarization effect in the studied PZT thin films. The increase of self-polarization with the film thickness increasing from 200 nm to 710 nm suggests that Schottky barriers and/or mechanical coupling near the film-substrate interface are not primarily responsible for the observed self-polarization effect in our films. (C) 2013 AIP Publishing LLC

A study on magnetoelectric phenomena in the barium titanate-barium hexaferrite (BaTiO3-BaFe12O19) composite system, using high resolution techniques including switching spectroscopy piezoresponse force microscopy (SSPFM) and spatially resolved confocal Raman microscopy (CRM), is presented. It is found that both the local piezoelectric coefficient and polarization switching parameters change on the application of an external magnetic field. The latter effect is rationalized by the influence of magnetostrictive stress on the domain dynamics. Processing of the Raman spectral data using principal component analysis (PCA) and self-modelling curve resolution (SMCR) allowed us to achieve high resolution phase distribution maps along with separation of average and localized spectral components. A significant effect of the magnetic field on the Raman spectra of the BaTiO3 phase has been revealed. The observed changes are comparable with the classical pressure dependent studies on BaTiO3, confirming the strain mediated character of the magnetoelectric coupling in the studied composites.

Electrostatic force microscopy (EFM) allows measurement of tiny changes in tip-sample capacitance. When nanoobjects are studied by EFM, they only contribute a very small fraction of the total capacitance between the tip and the sample. We show that the analysis of 3D maps of the EFM signal allows extracting the contribution of the nanomaterial to the total capacitance. This opens the way to applications of EFM as a measure of the dielectric coefficient of electrically insulating nanomaterials or the quantum capacitance of conducting nanomaterials. We apply this method to study the charge response of magnetite, Fe3O4, nanoparticles. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4790587]

Single phase Bi0.7La0.3FeO3 ceramic samples were successfully synthesized by sol-gel combustion and co-precipitation methods, performing a final sintering at 820-870 degrees C from 10 up to 180 min. Rietveld refinements of the XRD data detected small satellite peaks that were successfully indexed by an incommensurated modulated structure model. Lanthanum doping improves magnetic response, reduces the leakage current and dielectric losses. The piezoelectric coefficient was reported for the first time in the Bi0.7La0.3FeO3 composition. (C) 2012 Elsevier B. V. All rights reserved.

In this work we explore the formation of enhanced multiferroic interfaces in bismuth ferrite crystalline fibers grown by laser floating zone technique. An underlying mechanism of self-segregation during the fibers growth process enables to establish a textured microstructure of a dominant BiFeO3 phase bordered by the presence of Bi25FeO40 secondary phase. The crystallites c axis of the BiFeO3 phase shows a preferential orientation along the longitudinal axis of the fibers, together with grain boundaries that also present a significant alignment with the same direction. These features induce a systematic disturbance of the antiferromagnetic structure of the BiFeO3 phase at the interfaces with the Bi25FeO40 diamagnetic phase. The structural anisotropy confirmed by High Resolution X-ray diffraction and scanning electron microscopy images is also manifested in the magnetic properties of the fibers, which reveal an enhanced susceptibility response in comparison to the conventional BiFeO3 phase diagram. (C) 2015 Elsevier Ltd. All rights reserved.

Polycrystalline sample of lead-free 0.5Ba(Zr0.2Ti0.8)O-3-0.5(Ba0.7Ca0.3)TiO3 ceramic has been synthesized by solid state reaction method. Single-phase perovskite structure with rhombohedral symmetry was confirmed by x-ray diffraction. Temperature dependent dielectric permittivity studies demonstrated frequency independent behavior, indicating that the studied sample was not a typical relaxor ferroelectric. A polymorphic phase transition between rhombohedral and tetragonal phase was noticed near room temperature followed by a tetragonal to cubic transition with 97 degrees C as the temperature of maximum permittivity. The macroscopic values of d(33) and d(31) were similar to 350 pC/N and -141 pm/V, whereas the electromechanical coupling factors k(p) and k(t) were 44.5% and 41.6%, respectively. Bulk P-E hysteresis loop was obtained with saturation polarization 11 mu C/cm(2) and coercive field similar to 4 kV/cm. Distinct polarization contrast with a complex mosaic-like domain structure was observed in the out-of-plane mode of piezoresponse force microscopy. The domain width and the correlation length were estimated to be nearly 2 mu m and 827 nm, respectively. Local hysteresis loop with apparent coercive voltage, V-c = 15.8 V, was observed. (C) 2013 AIP Publishing LLC.

Dielectric and magnetic properties of the Bi1-x-yGdxLayFe1-yTiyO3 (x=0.1 and y=0.0, 0.1, 0.2, 0.3 and 0.5) solid solution ceramics have been presented this work. Effects of La substitution on the structural, electrical and ferroelectric properties of Bi1-x-yGdxLayFe1-yTiyO3 samples have been studied by performing X-ray diffraction and dielectric measurements as well as characterizing M-H hysteresis loop. The results indicate that, when La content exceeds 0.2, the crystal structure of the ceramic samples changes from rhombohedral to tetragonal phase. The maximum ferroelectric transition temperature (T-c) of this system was 190 degrees C with the dielectric constant peak of 2500 at 100 kHz for y=0.5. With increasing La content, the remanent magnetization increases and the coercive magnetic field decreases. (C) 2013 Elsevier Ltd. All rights reserved.