National Institute Of Materials Physics - Romania

The magnetic properties, in the 5 K-350 K temperature range, were investigated in relationship with the structure and morphology of Zn1-xFexO (x = 0, 0.01, 0.03) powders prepared by hydrothermal route. The magnetization measurements reveal that all powders are ferromagnetic at room temperature, with Curie temperature TT, higher than 350 K. The coercivity Hc takes values between 58 Oe and 107 Oe at 300 K and, between 217 Oe and 613 Oe at 5 K. The weak magnetization of the un-doped ZnO powder is temperature independent and was associated with the high surface to volume ratio of the powder particles (or the number of surface defects). The saturation magnetization M-s, was substantially enhanced (up to a factor of about 20 at 300 K and of about 200 at 5 K) at all temperatures as Fe concentration increased, in spite of reduction of the surface to volume ratio of the powder particles. The Hc vs. Tand FC/ZFC curves for the un-doped ZnO show typical ferromagnetic behavior, whereas for the Fe doped powders exhibit Ruderman-Kittel-Kasuya-Yosida (RKKY) - like and spin-glass-like behavior. The observed magnetic phenomena in Fe doped ZnO can be explained on the basis of "donor defects concentration magnetic cations concentration" phase diagram for dilute magnetic semiconductors. (C) 2017 Elsevier B.V. All rights reserved.

Measurements of the magnetocapacitance effect in epitaxial La0.7Sr0.3MnO3/Pb(Zr0.2Ti0.8)O-3/La0.7Sr0.3MnO3 heterostructures have been performed using a quasi-static method. Through capacitance-voltage measurements carried out under variable magnetic field it has been found that the magneto-capacitance depends on the orientation of the ferroelectric polarization. The value of magneto-capacitance can be as high as 1% in the voltage range near the ferroelectric coercive field. This has been attributed to a variation of the apparent built-in voltage of the PZT-LSMO Schottky barriers on applied magnetic field.

Bi3+, Pb2+ and Bi3+-Pb2+-containing aluminophosphate glasses were obtained by unconventional wet method, the molar formula of the glasses being: i) 58LiPO(3), 29Al(PO3)(3), 10Ba(PO3)(2), 3Bi(2)O(3); ii) 58LiPO(3), 29Al(PO3)(3), 10Ba(PO3)(2), 3PbO and iii) 6LiPO(3), 3Al(PO3)(3), 1Ba(PO3)(2), 10Bi(PO3)(3), 80Pb(PO3)(2). The glass samples were investigated to determine the density, the thermal expansion coefficients and the chemical stability. The magnetic measurements for Bi and Pb-single doped glasses revealed a diamagnetic behavior and those of Bi-Pb-containing glass disclosed a diamagnetic behavior superposed a small paramagnetic contribution, observed in low magnetic fields that can be attributed to the impurities presented in the matrix. The Verdet constant for the analyzed glasses appeared to have positive values proving a diamagnetic behavior of the investigated material. (C) 2016 Published by Elsevier B.V.

We report on the fabrication of silicon-reinforced carbon (C: Si) structures by combinatorial pulsed laser deposition to search for the best design for a new generation of multi-functional coated implants. The synthesized films were characterized from the morphological, structural, compositional, mechanical and microbiological points of view. Scanning electron microscopy revealed the presence, on top of the deposited layers, of spheroid particulates with sizes in the micron range. No microcracks or delaminations were observed. Energy dispersive x-ray spectroscopy and grazing incidence x-ray diffraction pointed to the existence of aC to Si compositional gradient from one end of the film to the other. Raman investigation revealed a relatively high sp(3) hybridization of up to 80% at 40-48 mm a part from the edge with higher Ccontent. Si addition was demonstrated to significantly increase C: Si film bonding to the substrate, with values above the ISO threshold for coatings to be used in high-loading biomedical applications. Surface energy studies pointed to an increase in the hydrophilic character of the deposited structures along with Si content up to 52 m Nm(-1'). In certain cases, the Si-reinforced Ccoatings elicited an antimicrobial biofilm action. The presence of Si was proven to be benign to HEp-2 cells of human origin, without interfering with their cellular cycle. On this basis, reliable C: Si structures with good adherence to the substrate and high efficiency against microbial biofilms can be developed for implant coatings and other advanced medical devices.

Hysteretic effects are investigated in perovskite solar cells in the standard FTO/TiO2/CH3NH3PbI3-xClx/spiro-OMeTAD/Au configuration. We report normal (NH) and inverted hysteresis (IH) in the J-V characteristics occurring for the same device structure, and the behavior strictly depends on the prepoling bias. NH typically appears at prepoling biases larger than the open circuit bias, while pronounced IH occurs for negative bias prepoling. The transition from NH to IH is marked by an intermediate mixed hysteresis behavior characterized by a crossing point in the J-V characteristics. The measured J-V characteristics are explained quantitatively by the dynamic electrical model. Furthermore, the influence of the bias scan rate on the NH/IH hysteresis is discussed based on the time evolution of the accumulated ionic and electronic polarization charge at the interfaces. Introducing a three-step measurement protocol, which includes stabilization, prepoling, and measurement, we put forward the difficulties and possible solutions for a correct photoconversion efficiency evaluation.

The substantial increase in the power conversion efficiency of hybrid perovskite solar cells, to date reaching more than 20% in the laboratory, has strongly motivated research on this class of organic-inorganic materials and related devices, particularly based on CH3NH3PbI3-xXx/TiO2 heterostructures (X = Cl,Br). Taking under consideration that a ferroelectric substrate may act as an efficient electron transporter, positively influencing charge collection across the interface and allowing the tuning of the halide perovskite (HP) - ferroelectric junction, we performed extensive density functional theory calculations on CH3NH3PbI3-xClx layers deposited on tetragonal PbTiO3 (PTO) (001) surfaces, to study their structural and electronic properties. The main findings of this study are as follows. (i) A ferroelectric polarization pointing from the PTO/HP interface to the PTO is favorable for the photogenerated electrons transfer across the interface and their transport to the collecting electrode. (ii) The PTO internal electric field leads to a position dependent energy levels diagram. (iii) The HP gap may be tuned by chlorine concentration at the interface, as well as the by the surface terminations of PbTiO3 and hybrid perovskite layers. (iv) The presence of the PTO ferroelectric surface is likely to have just a slight orientational effect on the (CH3NH3)(+) dipoles.

Two series of cyclometalated palladium(II) complexes based on Schiff bases and N-benzoylthiourea (BTU) ligands having four alkoxy groups at their periphery, with different number of carbon atoms, have been designed and prepared. The liquid crystalline behavior of these palladium(II) complexes was investigated by a combination of polarized optical microscopy (POM), differential scanning calorimetry (DSC) and powder X-ray diffraction while their thermal stability was studied by thermogravimetric analysis (TGA). The palladium(II) complexes are thermally stable on a broad temperature range up to 230 degrees C showing, depending on the alkoxy chain length, either monotropic or, for longest alkyl chain, enantiotropic smectic A and C phases. The luminescent properties of palladium(II) complexes were reported. These complexes show a yellow-orange solid-state emission at room temperature with two emission maxima at lambda(max) around 580 and 650 nm, respectively, with a shoulder around 710 nm, when the samples are irradiated in the 330-380 nm range. (C) 2017 Elsevier B.V. All rights reserved.

Pure BT and BT doped with 1 and 2 mol% Zr, with orthorhombic-tetragonal (O-T) phase transitions near room temperature were prepared, with different grain sizes, by conventional ceramic method, at various sintering temperatures. Intrinsic and extrinsic effects of Zr addition on structural, dielectric, piezoelectric and ferroelectric properties of BT ceramics, near O-T phase transition were studied. In coarse grained ceramics, the intrinsic effects manifested in low field measurements (dielectric and piezoelectric constants), were reduced by Zr addition, while the extrinsic effects which control the high field response (remanent polarization and coercive field) were significantly enhanced. Instead, in fine grains ceramics, of either pure or doped BT, the extrinsic effects related to increased domain wall and grain boundaries density were dominant in both low and high field measurements, overlapping Zr effects. The results were explained in terms of crystal anisotropy correlated with grain size effects.

Aluminum Nitride (AlN) thin films were synthesized on Si (100) wafers at 450 degrees C by pulsed laser deposition. A polycrystalline AlN target was multipulsed irradiated in a nitrogen ambient, at different laser pulse repetition rate. Grazing Incidence X-Ray Diffraction and Atomic Force Microscopy analyses evidenced nanocrystallites with a hexagonal lattice in the amorphous AlN matrix. The thickness and optical constants of the layers were determined by infrared spectroscopic ellipsometry. The optical properties were studied by Fourier Transform Infrared reflectance spectroscopy in polarised oblique incidence radiation. Berreman effect was observed around the longitudinal phonon modes of the crystalline AlN component. Angular dependence of the A(1)LO mode frequency was analysed and connected to the orientation of the particles' optical axis to the substrate surface normal. The role of the laser pulse frequency on the layers' properties is discussed on this basis. (C) 2016 Elsevier B.V. All rights reserved.

Epitaxial thin films of NiFe2O4 are fabricated by pulsed laser deposition on SrTiO3 substrate. Symmetrical capacitor-like structures are formed using SrRuO3 as bottom and top electrodes. Electrical characterizations, including current-voltage, capacitance-voltage and capacitance-frequency measurement, reveal a hysteresis-like behaviour for current and capacitance as function of voltage. This could be assigned to a resistive and/or capacitive switching. A "degradation" process takes place after repeated voltage cycling or after heating the sample to 400 K, leading to the stabilization of different resistive states. These features can be related to the changes observed in the capacitance-frequency characteristics, suggesting the presence of a relaxation mechanism at low frequencies, and can be associated with the presence of a deep donor-type level in the band-gap of the NiFe2O4 layer.