National Institute Of Materials Physics - Romania

Nano-sized lanthanum doped barium titanate Ba1-xLaxTiO3 (0.00 <= x <= 0.08) powders were prepared by sol-gel method. These powders with perovskite BaTiO3 cubic single phase structure, obtained after calcinations of gels precursors at 1100 degrees C, 3 h in air, were pressed and sintered by spark plasma technique in order to obtain dense ceramics. The optimal sintering temperatures used for Ba1-xLaxTiO3 powders were dependent on lanthanum amount added to barium titanate and decrease from 1300 degrees C to 1160 degrees C when the La concentration increases from 0 to 8 at.% La. An additional annealing treatment was made in air at 900 degrees C for all the sintered pellets for oxidize and remove the contaminant graphite which migrated in ceramics from the graphite die during the sintering process. The effect of lanthanum concentration on the densification behavior, structure, microstructure, photoluminescence and dielectric properties of the Ba1-xLaxTiO3 ceramics was investigated in this work. The results shown that as the lanthanum content increases, the grain size of the powders and ceramics increases accompanied by decrease of density of the samples. Also, increase of La amount inserted in BaTiO3 lattice leads to significant decrease of the dielectric losses and Curie temperature and, increase of dielectric permittivity but the luminescence properties seem to be less affected. (C) 2017 Elsevier B. V. All rights reserved.

Development of new sensitive materials by different synthesis routes in order to emphasize the sensing properties for hazardous H2S detection is one of a nowadays challenge in the field of gas sensors. In this study we obtained mesoporous SnO2-CuWO4 with selective sensitivity to H2S by an inexpensive synthesis route with low environmental pollution level, using tripropylamine (TPA) as template and polyvinylpyrrolidone (PVP) as dispersant/stabilizer. In order to bring insights about the intrinsic properties, the powders were characterized by means of a variety of complementary techniques such as: X-Ray Diffraction, XRD; Transmission Electron Microscopy, TEM; High Resolution TEM, HRTEM; Raman Spectroscopy, RS; Porosity Analysis by N-2 adsorption/desorption, BET; Scanning Electron Microscopy, SEM and X-ray Photoelectron Spectroscopy, XPS. The sensors were fabricated by powders deposition via screen printing technique onto planar commercial Al2O3 substrates. The sensor signals towards H2S exposure at low operating temperature (100 degrees C) reaches values from 10(5) (for SnWCu600) to 10(6) (for SnWCu800) over the full range of concentrations (5-30 ppm). The recovery processes were induced by a short temperature trigger of 500 degrees C. The selective sensitivity was underlined with respect to the H2S, relative to other potential pollutants and relative humidity (10-70% RH). (C) 2017 Elsevier B.V. All rights reserved.

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.

In the last decades, the study of magnetic fluids with different biomedical applications such as targeted delivery of a chemotherapeutic solution to the tumor site has been of high interest. For this purpose, ultrasonic and antimicrobial studies were used to characterize the aqueous solutions based on maghemite nanoparticles. The maghemite (-Fe2O3) and dextran-coated maghemite nanoparticles (DMNp) were synthesized by coprecipitation method. The spherical shape of the nanoparticles and uniform size with an average diameter around 9.5 +/- 0.5nm for -Fe2O3 were observed in transmission electron microscopy micrographs. Dynamic light scattering was used to determine the hydrodynamic size of -Fe2O3 nanoparticles and DMNp in suspensions. The hydrodynamic diameter obtained of -Fe2O3 and DMNp was 17 and 21nm, respectively. Moreover, a noninvasive method based on ultrasounds was used to characterize the aqueous solutions. The preliminary results showed the attainable accuracy in determining acoustic wave velocity and attenuation in various solutions. These data could be correlated with particle density and size. More than that, velocity and attenuation can be used as characteristic parameters of a given solution. A finite element model of the dispersed particles, correlated with measured velocity, allowed to solve for the elastic properties of the particles. POLYM. ENG. SCI., 57:485-490, 2017. (c) 2017 Society of Plastics Engineers

Sm3+ doped partially disordered calcium-niobium-gallium -garnet (CNGG) and calcium-lithium-niobium-gallium -garnet (CLNGG) single crystals were grown by the Czochralski method. Spectroscopic characteristics of Sm:CNGG and Sm:CLNGG single crystals were obtained by high-resolution absorption and emission spectra and emission dynamics measurements. Partial energy levels of Sm3+ doped CNGG and CLNGG were extracted from the measured spectra. The Judd-Ofelt theory has been applied to evaluate the Omega(t)(t=2,4, 6) intensity parameters, radiative transition rates A(r) branching ratios beta, and radiative lifetime tau(r), of the fluorescent Sm3+ (4)G(5/2) level. The emission cross-sections for the (4)G(5/2)-> H-6(J) (J=5/2, 7/2, 9/2) transitions of special interest for visible laser application were obtained by the Fucht-bauer - Ladenburg equation. The interaction between Sm3+ ions is dipole-dipole type and the C-DA, microparameter for both crystals was calculated based on Inokuti-Hirayama model. (C) 2017 Elsevier B.V. All rights reserved.

In quantum field theory, Weyl fermions are relativistic particles that travel at the speed of light and strictly obey the celebrated Lorentz symmetry. Their low-energy condensed matter analogs are Weyl semimetals, which are conductors whose electronic excitations mimic the Weyl fermion equation of motion. Although the traditional (type I) emergent Weyl fermions observed in TaAs still approximately respect Lorentz symmetry, recently, the so-called type II Weyl semimetal has been proposed, where the emergent Weyl quasiparticles break the Lorentz symmetry so strongly that they cannot be smoothly connected to Lorentz symmetric Weyl particles. Despite some evidence of nontrivial surface states, the direct observation of the type II bulk Weyl fermions remains elusive. We present the direct observation of the type II Weyl fermions in crystalline solid lanthanum aluminum germanide (LaAlGe) based on our photoemission data alone, without reliance on band structure calculations. Moreover, our systematic data agree with the theoretical calculations, providing further support on our experimental results.

This paper presents structural, morphological and preliminary ultrasonic characterizations of the -Cyclodextrin/hydroxyapatite (CD-HAp) composites synthesized by an adapted co-precipitation method. The structural and morphological properties were evaluated by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX). The specific surface area, pore size and pore volume were determined using the methods of Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH), respectively. The novelty of our study consists in preliminary ultrasonic measurements conducted on CD-HAp composite, uniformly dispersed in distilled water. The benefit of this non-destructive method was to facilitate and simplify the characterization techniques of nanoparticles. Our experiments proved that the efficiency of lead ion removal by CD-HAp composites depended on the initial concentration of lead. The maximum adsorption capacity of the solid phase, for Pb2+ indicated a higher rate of removal by the CD-HAp_2. These adsorption results bring valuable insight into the beneficial contribution of our compounds, for the removal of heavy metal ions from aqueous solutions. Furthermore, in the present study, was evaluated the toxic effect of lead ions adsorbed by hydroxyapatite from contaminated water on HeLa cells.

Compatibility of screen-printed piezoelectric 0.65Pb(Mg1/3Nb2/3) O-3-0.35PbTiO(3) thick films with metalized low-temperature co-fired (LTCC) ceramic substrates is examined. Such substrates are interesting for micro-electro mechanical systems, for example for piezoelectric sensors and actuators, where functional layers are usually Pb-based piezoelectrics. In this study the special attention is given to the influence of the Au, Ag and Ag/Pd electrode materials coated over the LTCC on the functional properties of the films. The best phase purity, dielectric and piezoelectric properties were obtained in the films on gilded substrates. No secondary phases were observed at the film/Au interface by scanning electron microscope. The piezoelectric coefficient d(33) of the films on gilded substrates is equal to 120 pC/N.