In this work, the magnetocaloric properties of (La0.45Nd0.25)Sr0.3MnO3 (LNSMO)-based composites are studied. The structural, microstructural, magnetic and magnetocaloric properties of LNSMO and LNSMO/5CuO samples were investigated aiming to particularly clarify the secondary phase (CuO) role in driving the magnetocaloric behavior. The main phase LNSMO crystallizes in a rhombohedral R-3C (1 6 7) configuration. The XRD patterns of composite samples show both perovskite LNSMO and monoclinic Tenorite CuO structures. The microstructural analysis unveils that the CuO phase is mainly present in the grain boundaries and segregates region. On the other hand, it was found that the magnetocaloric effect could be significantly enhanced by adding a small amount of CuO (5% weight ratio). For a magnetic field changing from 0 to 1.5 T, the corresponding isothermal entropy change was found to be 2.55 J/kg K for the LNSMO/5CuO composite while it is only about 1.1 J/kg K for the mother material LNSMO. Our finding should inspire and open new ways for the enhancement of the magnetocaloric effect in manganitesbased materials. (C) 2017 Published by Elsevier B.V.

In this work we report the synthesis, the microstructural characterization and the magnetic properties of tin spinel ferrites doped manganese (Sn1−xMnxFe2O4 with x=0.25, 0.5, 0.75, and 1) nanoparticles prepared by co-precipitation method. The effect of annealing temperature on the structure, morphology and magnetic properties of Sn0.5Mn0.5Fe2O4 has been investigated. The synthesized nanoparticle sizes have been controlled between 4 and 9nm, with uniform spherical morphology as confirmed by transmission electron microscopy (TEM). All the samples prepared possess single domain magnetic. The nanoparticles of Sn0.5Mn0.5Fe2O4 with 4nm in diameter have a blocking temperature close to 100K. In addition, the cation distribution obtained from the X-ray diffraction of this sample was confirmed by magnetic measurement. For the Sn1−xMnxFe2O4; (0≤x≤1) samples, the magnetization and coercive fields increase when the augmentation of Mn content increases. For x=0.5, such parameters decrease when the calcination temperature increases.

A new rare earth ferroelectric tetragonal tungsten bronze compound with general formula Ba2.15−x Na0.7+x Nb5−x W x O15 (x = 0.25) was elaborated as ceramic and investigated using X-ray diffraction and dielectric measurements. The results show a tetragonal phase with the space group P4bm. Special emphasis was done to characterize diffuse phase transition (DPT) that occurs close to 472 °C. Using dielectric measurements in a frequency range of (10 Hz–1 MHz) and in a temperature range (25–550 °C), we have shown that the real part of the permittivity close to DPT is well described by Santos–Eiras phenomenological model. Space charge polarization, relaxation phenomena and free charges conductivity have been analyzed using dielectric, impedance spectroscopy and Nyquist plots showed non-Debye (polydispersive) type relaxation. In paraelectric phase, the Arrhenius activation energies were determined. Frequency dependence of ac conductivity at different temperatures follows the Jonscher’s universal law (Jonscher et al. in J Mater Sci 20:4431, 1985).

In the present paper we report a one-pot synthesis of nanocrystalline, crack-free and mesoporous thin TiO2 films on graphite felt (GrF) and GrF terminated with NiO nanoleaflets. The films are obtained using an immersion method in an ethanolic solution of titanium isopropoxide containing small amounts of NH3 catalyser. A short heat treatment at 450 degrees C yields pure phase anatase directly on GrF or on the NiO nanoleaflets. The method allows processing of a variety of TiO2/metal oxide heterostructures and can be implemented for other catalysts. The supported films were tested for their photocatalytic activity using a continuous-flow set-up of an aqueous amido black solution under a cold UV diode at 360 nm. The results are compared to those of a thick macro-mesoporous P25-TiO2 film on Si. Full discoloration of the dye is obtained within 50 to 120 minutes for the films on the GrF substrates. The discoloration kinetics show a non-linear behaviour that is interpreted in terms of the rapid rarefication of the dye molecules. In contrast, the P25-TiO2 film on Si shows the usual linear behaviour with a small rate constant. The highest discoloration rate is obtained with TiO2 directly deposited on GrF. Based on the latest literature findings, it is postulated that the high defect density of the graphite structure could promote better charge separation and higher photocatalytic activity in comparison to the GrF/NiO/TiO2 heterostructure.

A 0.9BiFeO(3)-0.1Ba(0.8)Sr(0.2)TiO(3) ceramic is synthesized by conventional solid-state reaction method and investigated by structural, dielectric, thermal, Raman spectra and magnetization properties. The 0.9BiFeO(3)-0.1Ba(0.8)Sr(0.2)TiO(3) is crystallized in rhombohedral distorted perovskite structure with space group R3c. The dielectric loss is investigated over wide range of temperature at 100 kHz. During its evolution, an anomaly is observed at similar to 300 degrees C which corresponds to T-N (antiferromagnetic transition temperature). Besides, it is confirmed by DSC measurement. A magnetic property is confirmed by the temperature dependence of magnetization (M-T) under an applied magnetic field of 0.05 T. That revealed an antiferromagnetic transition of 0.9BiFeO(3)-0.1Ba(0.8)Sr(0.2)TiO(3) ceramic. The latter confirms which was previously mentioned. Furthermore, these results reveal considerable spectral changes in the vicinity of the Neel temperature T-N. Finally, this shift is discussed through structural, dielectric, thermal, vibrational and magnetic combination near the TN phase. (C) 2015 Elsevier B.V. All rights reserved.

The effects of Bi and Fe-excess on the structure, ferroelectric, leakage current and magnetic properties of BiFeO3 (BFO) thin films are reported. BFO with 5% excess exhibits no change in the structure with an improvement in leakage current properties in comparison to stoichiometric BFO. Raman spectroscopy of 10% Bi excess suggests a structural change from monoclinic to rhombohedral accompanied with an improvement of resistivity and ferroelectric polarization switching. A higher Fe-excess leads to the formation of pyrochlore Bi2Fe4O9 and gamma-Fe2O3 that cause an increase in conductivity at the macroscopic scale. The results are discussed in terms of Fe and Bi-excess effects on the defect structure of BFO.

Monolithic oxides whose lattice structures exhibit both ferroelectric and magnetic ordering and eventually intrinsic coupling between them are known as multiferroics. The possibility to switch magnetization by an electric field and reciprocally polarization by a magnetic field may allow new applications spanning the fields from new memory devices to medical measuring technology. Until now, the only monolithic oxide that has been shown to exhibit both (weak) magnetism and ferroelectric polarization at room temperature is BiFeO3 (BFO). However, as this material is a line compound, i.e., with sharply defined stoichiometry, its properties largely depend on defects and parasitic phases that could arise during processing. In the present work, we report on a new compound based on the solid solution GdMnO3–BiFeO3 (GdMBFO) that exhibit a fairly high magnetization coupled with moderate ferroelectric polarization at room temperature. Using conductive-tip atomic force microscopy, we show the highly electrically homogeneous microstructure. Ferroelectric polarization switching is obtained both as P-E hysteresis (or I-E) and capacitance-voltage butterfly curves. The effects of space charge on ferroelectric polarization that often bias polarization measurements reported for pure BFO are shown to be marginal. The high magnetization obtained for GdMBFO has allowed us to determine the Néel temperature (TN) directly from magnetic measurements. This results bears novelty as it is the first time that TN is reported for BFO-base thin films. The origin of magnetization improvement is discussed in terms of Gd substitution effects on octahedral distortion and tilting.

The results of structural studies of pure-phase perovskite thin films of BiFeO3–10% RMnO3 (R=La, Eu, Gd, Tb, and Dy) are presented. Raman scattering studies show line broadening similar to what is reported for RMnO3; they were attributed to Jahn–Teller distortion and orthorhombic structural change. Evidence of an anomaly of the orthorhombic distortion at GdMnO3 could be obtained. Interestingly the addition of GdMnO3 leads to a substantial increase in magnetization, combined with moderate ferroelectric polarization. All other compositions are characterized by higher ferroelectric polarization but almost no magnetization.

Thin films of TiO 2 ‐Pt nanocomposites containing 4 at% Pt have been processed via spin‐coating. Film characterization involved XRD, Raman as well as XPS and scanning surface potential microscopy (SSPM). After annealing at 500 °C the thin films consisted of nanocrystalline anatase and a few nm Pt nanoclusters. Annealing at 600 °C resulted in the formation of a high volume fraction of rutile, ∼70%, and a coarsening of the microstructure, including Pt nanoparticles which attained a mean particle size of up to 11 nm. These results contrasted with those of pure TiO 2 films obtained at 600 °C which showed only a limited amount of rutile formation, namely 9%. Raman spectra of Pt‐containing samples exhibited a fluorescence emission, as background to the Raman features, which was attributed to photoinduced luminescence from Pt nanoparticles supported by their surface plasmon resonance. Emission intensity being much higher in 600 °C film indicated a difference between the two films in terms of the (Pt) particle size and crystallinity, in agreement with the XRD results. XPS investigations revealed different oxidation states of Pt at the surface and in the film interior. The spectra suggested a slight oxidation of Pt at the surface while mainly metallic Pt was revealed in the film interior. The morphology and distribution of the Pt nanoparticles in the films annealed at 600 °C were investigated using SSPM. Discrete Pt nanoparticles, mainly distributed in the vicinity of TiO 2 grain boundaries were revealed. Nanocomposite film formation, Pt distribution and morphology are explained in terms of the limited solubility of Pt in the TiO 2 lattice and its higher surface energy in comparison to that of TiO 2 . Both effects are believed to lead to the formation of Pt nanoparticles at the (anatase or rutile) grain boundaries. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Ordered palladium nanowire (NW) arrays with high aspect ratio have been synthesized using porous alumina templates and direct-current electrodeposition. The porous alumina films were prepared by double anodizing high purity aluminium foils in oxalic and sulphuric acids at 40 and 25V, respectively. Final pore size of the processed (free-standing) alumina templates were determined to be ∼65 and 35nm. The electrolyte consisted of 70mM K2PdCl4 in 20mM H2SO4 and the deposition voltage was 0.3V (versus Ag/AgCl reference electrode). Under the employed conditions, a high filling rate (>90%) was obtained using 65μm thick templates. The NWs synthesized in 65nm pores were polycrystalline and textured, but those in 35nm pores were single-crystalline. It is suggested that deposition in smaller pores proceeds under smaller overpotential due to diffusion-limitation which favors single-crystalline growth. In order to obtain self-standing Pd NWs, which may be interesting for realizing NW-array based gas sensor structures, the alumina template was dissolved away, leaving self-standing NWs supported on a conductive thin film. Such NWs were observed to form agglomerates and chemisorb O and C as surface impurities.

In this work emphasis is placed on the investigation of interfacial layers between sol-gel processed PbTiO3 (PTO) thin films and (111)Pt terminated silicon substrates. The methods used are x-ray diffraction, x-ray photoelectron spectroscopy (XPS) combined with depth profiling, and atomic force microscopy (AFM). In order to avoid artifacts related to ion bombardment, e.g., reduction of Pb ions and preferential sputtering, gentle argon ion bombardment conditions were first derived. AFM investigations of native and ion bombarded films at different stages of depth profiling show that the films are homogenously sputtered, whereby the film roughness remains practically unchanged in the course of sputtering. An annealing treatment at 550 °C under reducing atmosphere was used to provoke the formation of an interfacial intermetallic (111)PtxPb phase, which is shown to coexist with an amorphous oxide film. This could allow us to establish the XPS signature of the intermetallic phase. A negative shift of the Pt (4f) binding energy and a large full width at half maximum of the Pb (4f) peak are the attributes of this signature. PTO-film annealing in air at temperatures between 350 and 600 °C leads to the formation of the perovskite phase, starting at 500 °C, directly from the amorphous phase. Based on its derived XPS signature it is shown that the intermetallic phase still exists at the interface with variable thickness depending on the annealing temperature. The pronounced (111) texture of the PTO-crystallized films is thought to be the direct consequence of this intermetallic template layer. It is also shown that the outermost surface of the PTO film is enriched with PbO as a result of segregation phenomena.

The influence of ultraviolet (UV) light during pyrolysis of sol-gel fabricated Pb(Zr0.52Ti0.48)O-3 thin films on (111)Pt/Ti/SiO2/Si substrates has been investigated. The UV treated films show a homogeneous fine grain structure with (100) preferential orientation, whereas a bimodal grain structure and (111) preferential orientation were found for the untreated film. This is explained in terms of specific template layers formed during pyrolysis. The ferroelectric, dielectric and piezoelectric properties are also reported for both films. It is shown that while the ferroelectric properties are higher for the (111) films, the (100) films show better dielectric and piezoelectric properties with an effective piezoelectric coefficient, d(33eff,) of 183 pm/V vs. 101.8 pm/V for the (111) films.

Thin films of the BiFeO3–LaMnO3 solid solution were processed on (111)-Pt∕Ti∕SiO2∕Si substrates via spin coating. Microstructure, and leakage current, ferroelectric and magnetic properties are reported. It is shown that the addition of 5mol% LaMnO3 substantially improves the properties. Leakage currents that are several orders of magnitude lower than those of pure BiFeO3 were obtained. The leakage currents follow the Poole-Frenkel mechanism, and a trap depth of 0.94eV was obtained. The addition of LaMnO3 resulted in saturated polarization hysteresis loops with a high remnant polarization 2Pr of 88μC∕cm2. Finally, LaMnO3 also leads to higher coercive fields but smaller saturation magnetization.

BiFeO 3 thin films were processed on La0.8Sr0.2MnO3 (LSMO) buffered silicon substrate via chemical solution deposition. Short-wave ultraviolet assisted pyrolysis was conducted in oxygen atmosphere in order to improve microstructure. A fine, homogeneous, and phase-pure grain structure with smooth topography was obtained. X-ray photoelectron spectroscopy analysis indicates diffusion of lanthanum and manganese from LSMO into the BiFeO3 film leading to a diffuse interface. Nevertheless, improved polarization and leakage resistance properties were obtained. For the first time polarization switching was obtained in sol-gel BiFeO3 films using capacitance-voltage (C−V) curves. This has been imputed to homogeneous local electrical properties of the film, corroborated by surface scanning potential microscopy investigations. The leakage current mechanisms were investigated as function of temperature, and could be interpreted in terms of the Frenkel-Poole mechanism with a trap depth of 1.6 eV. Finally, the magnetic properties of the LSMO∕BiFeO3 heterostructure are presented in comparison to those of BiFeO3 on platinized silicon. An exchange coupling between BiFeO3 and LSMO layers is suggested.

BiFeO3 thin films were processed on platinized silicon substrate via chemical solution deposition. Short wave UV assisted pyrolysis was conducted in oxygen atmosphere in order to obtain a fine and homogeneous grain structure. Phase pure thin films with a pronounced (100) texture were obtained at a fairly low annealing temperature of 600°C. For comparison specimens processed without UV assisted pyrolysis were also investigated. It is shown that UV assisted pyrolysis leads to a substantial improvement of leakage resistance properties. Polarization switching could also be obtained using capacitance-voltage (C-V) curves. The leakage current was investigated as a function of temperature. Interpretation in terms of Frenkel-Poole mechanism leads to a high trap depth in the range of 2.4 eV which is attributed to the creation of Fe2+ centres. For both microstructures investigated well saturated magnetization loops were obtained with a remnant magnetization of 2Mr = 5.4 emu/cm3 and a coercive fields in the range of 2Hc = 200 Oe. Slightly higher saturation magnetization 2Ms of 55.4 emu/cm3 was obtained for UV assisted pyrolysis in comparison to 45.8 emu/cm3 for the thin films processed without UV.