Adelina Ianculescu

Functional properties of BaTiO3–Ni0.5Zn0.5Fe2O4 magnetoelectric ceramics prepared from powders with core-shell structure

In the present work, diphasic ceramic composites with core-shell nanostructures formed by Ni0.50Zn0.50Fe2O4 core and BaTiO3 shell were investigated. Their properties were compared with those of composites prepared by coprecipitation. The core-shell structure was confirmed by microstructural powder analysis. Homogeneous microstructures with a good phase mixing and percolated dielectric phase by the magnetic one were obtained from coprecipitated powders. Less homogeneous microstructures resulted in ceramics produced from the powder prepared by core-shell method, with isolated small ferrite grains besides large ferrite aggregates embedded into the BaTiO3 matrix. Both the ferroelectric and magnetic phases preserve their basic properties in bulk composite form. However, important differences in the dielectric relaxation and conduction mechanisms were found as result of the microstructural difference. Extrinsic contributions play important roles in modifying the electric properties in both ceramics, causing spa...

High-field dielectric properties and Raman spectroscopic investigation of the ferroelectric-to-relaxor crossover in BaSnxTi1−xO3 ceramics

BaSnxTi1−xO3 solid solutions with compositions in the range x = 0–0.20 were studied by combining analysis of the field-induced dielectric and ferroelectric properties with Raman spectroscopic investigations. By combining techniques, the detection of specific features related to the ferroelectric-to-relaxor crossover with increasing Sn content is possible. Detailed tunability analysis of the x = 0.05 composition indicated that multiple components contribute to the dc-field induced permittivity response; these components are active in different temperature and field ranges and could be assigned to a few polarization mechanisms. First order reversal curves (FORC) for the material clearly show a transition from ferroelectric-to-relaxor behavior with increasing x, confirming the conclusions from the Raman and dielectric studies. This was evidenced by the shift of the FORC distribution over coercivities toward zero field values. Raman measurements allow the identification of the separate phases with varying Sn ...

Differentiation of mesenchymal stem cells onto highly adherent radio frequency-sputtered carbonated hydroxylapatite thin films.

In this work, an improved version of the radio frequency magnetron sputtering (RF-MS) technique was used to prepare highly adherent B-type carbonated hydroxylapatite (B-CHA) thin films. Fourier transform infrared spectroscopy (FTIR) and grazing incidence X-ray diffraction studies proved that the coatings maintained the composition and revealed the polycrystalline structure of HA. Scanning electron microscopy analysis showed that the CHA films are rough and exhibit a homogeneous microstructure. Energy-dispersive X-ray spectroscopy (EDX) mapping demonstrated a uniform distribution of the Ca and P cations while a Ca/P ratio of 1.8 was found. In addition, the FTIR experiments showed a remarkable reproducibility of the nanostructures. Human mesenchymal stem cells (hMSCs), in vitro differentiated osteoblasts, and explanted bone cells were grown over the surface of CHA coatings for periods between a few hours and 21 days. Osteoprogenitor cells maintained viability and characteristic morphology after adhesion on CHA coatings. Ki67-positive osteoblasts were the evidence of cell proliferation events. Cells showed positive staining for markers of osteoblast phenotype such as collagen type I, bone sialoprotein and osteonectin. Our data showed the formation of mineralized foci by differentiation of hMSCs to human primary osteoblasts after cultivation in osteogenic media on RF-sputtered films. The results demonstrate the capacity of B-type CHA coating to support MSCs adhesion and osteogenic differentiation ability.

Properties of Ba1−x Sr x TiO3 Ceramics Prepared by the Modified-Pechini Method

Single phase Ba 1−x Sr x TiO 3 powders (x = 0; 0.20; 0.25; 0.30 and 0.35) were obtained via modified Pechini method after annealing of the polymeric precursors in air at 850°C for 2 hours. When the strontium content, x, increases, the tetragonality degree decreases, so that the unit cell symmetry changes from a tetragonal one, specific to the pure BaTiO 3 powder towards a cubic form, for powders with x ≥ 0.30. Dense and homogeneous microstructures, free of secondary phases were obtained for the related ceramics resulted after sintering in air, at 1350°C for 3 hours. High values of the relative permittivity (of ∼ 1500–12000) and low dielectric losses were obtained at the room temperature for all the compositions.

TiO2-based Nanomaterials with Photocatalytic Properties for the Advanced Degradation of Xenobiotic Compounds from Water. A Literature Survey

In recent years, the photochemistry of nano-semiconductor particles has been one of the fastest growing research areas in the physical chemistry field. TiO2 is considered as the most thoroughly investigated semiconductor in the literature, due to its photocatalytic activity, excellent functionality, thermal stability, and non-toxicity. It seems to be the most promising for the photocatalytic destruction of organic pollutants. The challenge for scientific materials is to find a processing method in which the crystalline phase as well as the size and morphology of TiO2 nanocrystals can be controlled. The concept of the present paper consists of a comprehensive study regarding the level of knowledge in the synthesis of TiO2-based nanopowders and their application in the advanced degradation of aromatic nitrocompounds. The objectives are related to: critical analysis of the synthesis techniques of the TiO2-based nanopowders, underlining the importance of using the sol–gel method evaluation of the morphological and structural specific characterization of these techniques; and a comprehensive study of the operational parameters of the pollutant photocatalytic degradation. The relative simple sol–gel method is the most widely used, being considered as a versatile means of developing catalytic materials, as well as an important experimental tool in understanding their physical and chemical properties. In order to enhance TiO2 photocatalysis and to extend the response into the visible domain, titanium has been doped with metals, nonmetals, and ionic components. A recent literature survey concerning some transition metals-doping (Fe, Co, and Ni) of TiO2 nanopowders by the sol–gel method was also included.

Structural characteristics of RF-sputtered BaTiO3 thin films

Abstract In this work some structural characteristics of the thin films deposited by a radio frequency-magnetron sputtering technique from a hot pressed BaTiO3 ceramic target were studied. The Ba/Ti ratio was measured by means of X-ray fluorescence in order to determine the real chemical composition of the films. The results showed that this ratio varied along the radial axis of the discharge. Besides, the evolution in phase composition of the annealed films as a function of the thermal treatment conditions (temperature and plateau) as well as the structural characteristics (unit cell parameter and crystallite size) were investigated by X-ray diffraction (XRD). Infrared (IR) and Raman spectroscopies were used in order to obtain more details about the distorted structure of such fine-grained thin films. In the case of these films, Raman spectroscopy carried out from 99 to 473 K did not emphasize steep, distinct transitions between the different polycrystalline BaTiO3 forms when compared with the bulk BaTiO3.

Radical modification of the wetting behavior of textiles coated with ZnO thin films and nanoparticles when changing the ambient pressure in the pulsed laser deposition process

Cotton/polyester woven fabrics were functionalized with ZnO thin films or nanoparticles by pulsed laser deposition, using a KrF* excimer laser source. Depending on the number of applied laser pulses, well-separated nanoparticles (for 10 pulses) or compact thin films (for 100 pulses) were deposited. The synthesized nanostructures were evaluated morphologically by scanning electron microscopy and atomic force microscopy, physico-chemically by x-ray diffraction and functionally by the contact angle method. By modifying the ambient gas nature and pressure in the deposition chamber, hydrophilic or hydrophobic surfaces were obtained. When using an oxygen flux, both the deposited thin films and nanoparticles were hydrophilic. After deposition in vacuum, the nanoparticles were hydrophobic, but the thin films were super-hydrophobic. This radical modification of wetting behavior was assigned to the differences in microstructure features and surface electrical charging in the two cases.

Temperature dependence of tunability of Ba(SnxTi1−x)O3 ceramics

The electric field dependence of the dielectric constant (dc-tunability) as a function of temperature for a few compositions of Ba(Sn,Ti)O3 ceramics was investigated. Dense and homogeneous BaSnxTi1−xO3 ceramics (ferroelectric for x = 0.05 and x = 0.10, relaxor for x = 0.15 and 0.20) with high dielectric constant and low dielectric losses were prepared by solid state reaction. Their dc-tunability characteristics were investigated at a few temperatures from 20–120 °C, including the Curie range. The tunability data were discussed in terms of the Johnson model completed with a Langevin term that describes the “extrinsic” contribution to the nonlinear ɛ(E) dependences.

Biopolymer starch mediated synthetic route of multi-spheres and donut ZnO structures

A starch-assisted synthetic methodology of multispheres ZnO-starch biocomposites was developed. An additional thermal processing of the ZnO-starch composites induces the formation of ZnO with donut-like morphology. The synthesis of single-phase zinc oxide with a spherical morphology is conditioned by the presence of starch, which acts as template, stabilizing/capping agent. The synthesized structures present significant photocatalytic activities; a total phenol mineralization is attained with the donut-like ZnO photocatalyst under visible light irradiation, due to a cumulative effect of the its relatively large specific surface area, high crystallinity and favorable combination of defects for band narrowing, which together permit an enhanced utilization rate of the light.

Non-linear dielectric properties of BiFeO3 ceramics

The nonlinear dielectric properties of BiFeO3 ceramics as a function of temperature were investigated. The present results demonstrate a high dielectric tunability in quite low range of the bias electric fields over a broad temperature interval around the room temperature. The non-linear permittivity-field response results from multiple contributions, whose weights are different at various temperatures and in different field ranges.