National Institute Of Materials Physics - Romania

In this work, polyvinylidene fluoride was obtained in the form of one-dimensional structures with the help of electrospinning technique. Several types of precursor solutions were tested to find the optimal experimental conditions to produce smooth, continuous and beadless fibres, morphologically suitable for the development of piezoelectric scaffolds dedicated to tissue engineering applications. Thus, the influence of solvent type, polymer concentration, as well as electrospinning parameters (feeding rate, spinneret-collector distance, and applied voltage) was assessed and the best situation was the one with a 2:3 ratio between dimethylformamide and acetone, 20 % polymer concentration, 1 mL/h flow, 20 cm distance and 18 kV voltage. In the end, the fibres were loaded with barium titanate commercial particles, as first attempt to produce a piezoelectric composite with potential in the medical field.

The low-energy electron irradiation improves the electrical properties of the Ti-doped chromium thin films obtained by Laser-assisted Thermionic Vacuum Arc (LTVA). The irradiation doses, between 0.6 C/m(2) and 326.4 C/m(2), operate as a nanozonal melting effect, decreasing the metallic alloy's roughness, and increasing the electrical conductivity at a depth up to 8 nm. Therefore, the grain sizes of the surface nanostructures are increased after irradiation, but the surface roughness is substantially improved. By tailoring the surface parameters like crystallinity and roughness of the metallic thin films used as electrodes in the OLED technologies, a reduction of the Schottky contacts between the metal and semiconductor contact is expected. This fact minimizes the contact resistance between the metallic and semiconductor thin films and increases the charge injection across the OLED sandwich structures.

This work reports the effect of the rapid solidification technique and thermal treatment on the martensitic transformation (MT), magnetic and magnetostrictive properties on the off-stoichiometric Ni49Mn31Ga20 and Ni51Mn28Ga21 ferromagnetic shape memory ribbons. The samples were investigated by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, magnetic and magnetostrictive measurements. The temperature dependence of the X-ray phases analysis shows the presence of martensite structures, both tetragonal and monoclinic, at room temperature and allowed to study their evolution through MT. The thermal treatment induces changes in the microstructure with implications in MT and Curie temperatures evolution. The competition between the magnetization orientation and twin boundary motion within martensitic variants under magnetic field evidenced in the magnetic-strain curves was discussed and correlated with the magnetic data.

Zr0.8Sn0.2TiO4 powders synthesized by solid state reaction route have been consolidated by conventional and spark plasma sintering methods. Single-phase ceramics with various microstructures and, consequently, different extrinsic absorption were investigated by terahertz time-domain spectroscopy. The results showed that the terahertz spectroscopy can be used for tailoring in the " synthesis - microstructure - properties" cycle.

The local crystal/magnetic structures of the SrFe12-xInxO19 solid solutions (x = 0.1; 0.3; 0.6 and 1.2) were investigated using neutron powder diffraction. The measurements of the electric polarization for all investigated samples were carried out as a function of the external electric field. The presence of the ferroelectric and ferromagnetic ordering (dual ferroic ordering) in the SrFe12-xInxO19 hexaferrites at 300 K was found. This appearance contradicts to the conventional opinion describing their crystal structure (centrosymmetric space group P6(3)/mmc (No. 194)). The reason for the existence of a spontaneous polarization (nonzero dipole moment) in the SrFe12-xInxO19 hexaferrites continues controversial. The crystal structure of the hexaferrites was considered both the centrosymmetric P6(3)/mmc and non-centrosymmetric P6(3)mc space groups. This fact made it possible to find a connection between the emerging dipole moment and not equal distortions of the neighbor oxygen polyhedral. The nature description of the nonzero dipole moment formation in a quasi-centrosymmetrical system of the In-substituted SrFe12-xInxO19 hexaferrites was presented based on the neutron diffraction data. (C) 2021 Elsevier B.V. All rights reserved.

Piezoelectric hard/soft effects of multivalence co-dopants (Sb and Mn) in correlation with their location in the lattice, were investigated in PZT ceramics, prepared by conventional ceramic technology, with the following compositions: Pb0.98Sr0.02 ((Ti0.49Zr0.51)(1-0.015-x)Mn0.015Sbx)O-3 with x = 0, 0.005, 0.01, 0.02, 0.03, where antimony was initially assumed to substitute for Ti/Zr ions. The antimony valence state was found to be +3 in all samples by X-ray Photoelectron Spectroscopy investigations. The Electron Paramagnetic Resonance spectra evidenced a steep enhancement of the Mn2+ concentration upon increasing antimony doping level, explained by a charge compensation mechanism, between the Sb3+ ions substituting Pb2+ at the A-sites and the Mn2+ ions, localized at the B-sites. The incorporation of Sb3+ at the A-site of the PZT lattice is also supported by the variation of the lattice parameters, determined by X-ray Diffraction, with the increasing Sb concentration. The investigation of the dielectric, electromechanical and ferroelectric properties evidenced a hard piezoelectric behavior, mainly attributed to the presence of large sized Mn2+ ions, localized at B-sites. Our results prove that the piezoelectric hard/soft response is decisively influenced by the interplay between multiple valence states and locations of the co-dopants, on one hand, and the charge compensation mechanisms, on the other hand. This provides indirect information about the location of some co-dopants which can substitute for both cationic sites in the PZT based ceramics.

In this study, we develop chitosan-hydroxyapatite (CS-HAp) composite layers that were deposited on Si substrates in radio frequency (RF) magnetron sputtering discharge in argon gas. The composition and structure of CS-HAp composite layers were investigated by analytical techniques, such as Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), metallographic microscopy (MM), and atomic force microscopy (AFM). On the other hand, in the present study the second order derivative of FT-IR-ATR spectra, for compositional analyses of CS-HAp, were used. The SEM, MM, and AFM data have shown the formation of CS-HAp composite layers. The surface of CS-HAp composite layers showed uniform growth (at an Ar gas working pressure of p = 2 x 10(-3) mbar). The surface of the CS-HAp composites coatings became more nanostructured, becoming granular as the gas pressure increased from 5 x 10(-3) to 1.2 x 10(-2) mbar. However, our studies revealed that the surface morphology of the CS-HAp composite layers varies with the Ar gas working pressure. At the same time, optical properties are slightly influenced by Ar pressure. Their unique physicochemical properties make them suitable for various applications in the biomedical field, if we consider the already proven antimicrobial properties of chitosan. The antifungal properties and the capacity of the CS-HAp composite layers to inhibit the development of fungal biofilms were also demonstrated using the Candida albicans ATCC 10231 (C. albicans) fungal strain.

Hydroxyapatite (Ca-10(PO4)(6)(OH)(2), HAp), due to its high biocompatibility, is widely used as biomaterial. Doping with various ions of hydroxyapatite is performed to acquire properties as close as possible to the biological apatite present in bones and teeth. In this research the results of a study performed on thin films of hydroxyapatite co-doped with nitrogen and bromine (NBrHAp) are presented for the first time. The NBrHAp suspension was obtained by performing the adapted co-precipitation method using cetyltrimethylammonium bromide (CTAB). The thin layers of NBrHAp were obtained by spin-coating. The stability of the NBrHAp suspension was examined by ultrasound measurements. The thin layers obtained by the spin-coating method were examined by scanning electron microscopy (SEM), optical microscopy (OM), and metallographic microscopy (MM). The presence of nitrogen and bromine were highlighted by energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) studies. Fourier transform infrared spectroscopy (FTIR) was used to highlight the chemical status of nitrogen and bromine. In addition, the powder obtained from the NBrHAp suspension was analyzed by XRD. Moreover, the in vitro antimicrobial activity of the NBrHAp suspensions and coatings was investigated using the reference microbial strains Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, and Candida albicans ATCC 10231. The results highlighted the successful obtainment of N and Br co-doped hydroxyapatite suspension for the first time by an adapted co-precipitation method. The obtained suspension was used to produce pure NBrHAp composite thin films with superior morphological properties. The NBrHAp suspensions and coatings exhibited in vitro antimicrobial activity against bacterial and fungal strains and revealed their good antimicrobial activity.

Nanoscale thermometers with high sensitivity are needed in domains which study quantum and classical effects at cryogenic temperatures. Here, we present a micrometer sized and nanometer thick chromium selenide cryogenic temperature sensor capable of measuring a large domain of cryogenic temperatures down to tenths of K. Hexagonal Cr-Se flakes were obtained by a simple physical vapor transport method and investigated using scanning electron microscopy, energy dispersive X-ray spectrometry and X-ray photoelectron spectroscopy measurements. The flakes were transferred onto Au contacts using a dry transfer method and resistivity measurements were performed in a temperature range from 7 K to 300 K. The collected data have been fitted by exponential functions. The excellent fit quality allowed for the further extrapolation of resistivity values down to tenths of K. It has been shown that the logarithmic sensitivity of the sensor computed over a large domain of cryogenic temperature is higher than the sensitivity of thermometers commonly used in industry and research. This study opens the way to produce Cr-Se sensors for classical and quantum cryogenic measurements.