Publications

A new class of thermotropic lanthanidomesogens has been designed and prepared. They are based on 4-pyridone ligands that possess mesogenic cyanobiphenyl groups attached to the 4-pyridone unit via a flexible long alkyl spacer and show a very high thermal stability (decomposition temperatures near 300 degrees C). Depending on the alkyl length spacer, these complexes exhibit a SmA phase with transition temperatures influenced by the number of mesogenic groups employed and the spacer length.

Samarium doped hydroxyapatite (Sm:HAp), Ca10-xSmx(PO4)(6)(OH)(2) (HAp), bionanoparticles with different x(Sm) have been successfully synthesized by coprecipitation method. Detailed characterization of samarium doped hydroxyapatite nanoparticles (Sm: HAp-NPs) was carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). The biocompatibility of samarium doped hydroxyapatite was assessed by cell viability. The antibacterial activity of the Sm: HAp-NPs was tested against Gram-negative bacteria (Pseudomonas aeruginosa and Escherichia coli) andGram-positive bacteria (Enterococcus faecalis and Staphylococcus aureus). A linear increase of antimicrobial activity of P. aeruginosa has been observed when concentrations of Sm: HAp-NPs in the samples with x(Sm) = 0.02 were higher than 0.125 mg/mL. For Sm: HAp-NPs with x(Sm) = 0.05 a significant increase of antibacterial activity on E. coli was observed in the range 0.5-1 mg/mL. For low concentrations of Sm: HAp-NPs (x(Sm) = 0.05) from 0.031 to 0.125 mg/mL a high antibacterial activity on Enterococcus faecalis has been noticed. A growth of the inhibitory effect on S. aureus was observed for all concentrations of Sm: HAp-NPs with x(Sm) = 0.02.

New type of dielectric resonator antennas (DRAs) with axial symmetry are proposed for frequencies around 5.8 GHz. Each element uses a high permittivity cylindrical resonator and a low permittivity resonator of a truncated cone shape. Two types of microstrip-fed DRAs were investigated. By coupling the resonance modes, the first type and the second type DRA exhibit fractional impedance bandwidth of 15.6% and 19.7%, respectively.

The paper presents a CDRA (Cylindrical Dielectric Resonator Antenna) designed for wireless military and commercial applications. The antenna has been designed to radiate at 6.7 GHz, with a 160 MHz bandwidth at -10 dB. The antenna is made from a dielectric material with high quality factor. The dielectric resonator is Ba1-xPbxNd2Ti5O14 (BNT) and its relative permittivity has a value of 55.2. The feed technique used is direct coupling to micro strip-line.

In this paper we report electro-optic (EO) sampling of THz pulses using ferroelectric crystal in the non-collinear Cherenkov phase-matching scheme, where an effective velocity matching is achieved in an EO crystal with a large refractive index in the THz frequency region. We demonstrate efficient THz EO sampling using LiNbO3 and BaTiO3 crystals in the Cherenkov-phase-matching scheme. It is shown that the efficiency of EO sampling with BaTiO3 is smaller than that with LiNbO3, even though the EO coefficient (r(33)) of BaTiO3 is three times higher than that of LiNbO3. The reason of the poor performance of BaTiO3 is attributed to the strong absorption in the THz frequency region.

The leakage current was studies in epitaxial ferroelectric Pb(Zr0.52Ti0.48)O-3 layer with common SrRuO3 bottom electrode and different metals as top contacts (SrRuO3, Pt, Ir, Ru). It was found that the dominant conduction mechanism in the 200-350 K temperature range and for voltages significantly larger than the coercive value is the thermionic emission governed by the Schottky-Simmons equation. The height of the potential barriers was estimated and was found that this is about the same for negative and positive voltage polarities. No correlation was found between the height of the potential barriers for different top contacts and the work function difference between the bottom and top electrodes. The results suggest that the potential barrier is controlled by the polarization charges in a similar way to the one reported for Pb(Zr0.2Ti0.8)O-3 and BaTiO3 epitaxial films with bottom SrRuO3 electrode and different metals as top contacts. It was also found that above 350 K the conduction mechanism changes to ohmic and/or space charge limited currents.

The aim of this study was to investigate the influence of Ca10-x Eu-x(PO4)(6)(OH)(2), ( x(Eu)=0; 0.05) before and after immersion in simulated body fluid (SBF) for 72 hours. The samples have been investigated by X-Ray Diffraction, FT-IR Spectroscopy, Raman Spectroscopy and Steady-State Photoluminescence. Moreover, it was studied the antibacterial activity of the powders against Staphylococcus aureus and Escherichia coli bacterial strains. Our studies revealed that after soaking in SBF solution, the average crystallite size of the samples increased. Moreover, it was noticed that the luminescence of the samples is strongly influenced by the immersion in SBF solution.

In this paper electrical conductivity analysis of a new material, designed to be used as a solid electrolyte for intermediate temperature fuel cells (IT-SOFC) was performed. The material is based on a composite of scandia doped ceria (SDC) and yttria doped alumina (YA) which ensures higher mechanical stability. The initial powders were obtained by sol-gel method. The samples were prepared by cold pressing and sintering at 1500 degrees C. Materials with variation of the composition (SDC/YA = 95/5; 90/10, 85/15 mass %) were studied. The conductivity was determined by Electrochemical Impedance Spectroscopy. According of the electrochemical analysis the composites with 5 and 10 mass % YA exhibit better conductivity. The results are in correlation with morphological investigation, realized by SEM.