Publications

In this work the screen-printed piezoelectric 0.65Pb(Mg1/3Nb2/3)O-3-0.35PbTiO(3) thick films were prepared on metalized low-temperature co-fired ceramic substrates. Such substrates are interesting for micro-electro mechanical systems, for example for piezoelectric sensors and actuators. The prepared thick films exhibit the piezoelectric coefficient d(33) equal to 120 pC/N.

This paper presents the synthesis and characterization of hydroxyapatite (HAp) and hydroxyapatite embedded in a collagen matrix (C-HAp6). The aim of this study was to investigate the influence of collagen on the structure and morphology of hydroxyapatite. According to the XRD patterns, the samples have the structure characteristic to hydroxyapatite. The FTIR and Raman spectra proved the successfully embedding of hydroxyapatite in the collagen matrix. Morphologically, the collagen increases the porosity of HAp. The collagen influences the structure and morphology of the hydroxyapatite causing a decrease of the mean particle size and/or a decrease of crystallinity while increasing the porosity.

The XRD analysis were performed to confirm the formation of hydroxyapatite structure in collagen-silver-hydroxyapatite nanocomposites. The molecular interaction in collagen-hydroxyapatite nanocomposites was highlighted by Fourier transform infrared spectroscopy (FTIR) analysis. The SEM showed a nanostructure of collagen-silver-hydroxyapatite nanocomposites composed of nano needle-like particles in a veil with collagen texture. The presence of vibrational groups characteristics to the hydroxyapatite structure in collagen-silver-hydroxyapatite (AgHApColl) nanocomposites was investigated by FTIR.

Bioactive composites of bovine derived hydroxyapatite and boron containing bioactive glass were doped with 5, 10 and 15 wt.% lanthanum oxide (La2O3). Results showed that at low sintering temperatures (800 degrees C) the doping oxide of La2O3 promoted transformation to crystalline phases. Formation of secondary phases, such as rhenanite, NaCaPO4, and calcium silicate, Ca2SiO4, were also found. La was found to act as modifier and influenced the viscosity. The increase of La2O3 content led to decrease of pore size. Porosity amount 48.1 %, at 15-240 mu m size range were reduced, to 34.4 %, with 5-80 mu m size range and particle sizes of 0.3-6 mu m to 0.09-2 mu m, respectively. In addition to that compression strength (MPa) and microhardness (HV) of the performed composite bioceramics were in the range of 25 - 110 MPa, and 121 - 364 HV, respectively. Our investigations suggested that the porosity type has a strong influence on the compressive strength and microhardness properties of the final bioceramic products.

Nanotubes of Ba0.95Ce0.05Ti0.9875O3 with an average diameter of 80 nm and wall thickness of similar to 8 nm were prepared from the precursor sol using as template a polycarbonate membrane with the pores diameter size of 100 nm. The Ce doped-BaTiO3 nanotubes calcined at 700 degrees C, 1h in air crystallized on the lattice of BaTiO3 cubic phase as indicated the high resolution transmission electron microscopy and selected area electron diffraction analyses. The nanotubes showed a polycrystalline structure with crystallites of 3-5 nm size. The results prove that we can prepare BaTiO3 doped with 5 at.% Ce nanotubes for future capacitor applications.

The europium doped hydroxypatite samples were obtained by an adapted coprecipitation method. After the synthesis, the samples were immersed in simulated body fluid (SBF) solution for 6 and 24 h respectively. After the immersion in the SBF solution, the morphology and antimicrobial activity of the powders were studied. Our antimicrobial studies revealed that all the samples exhibit antimicrobial activity against gram positive and gram negative strains.

Nanoparticle system with the composition xEu(2)O(3)-(1-x)alpha-Fe2O3 (x = 0.1 and 0.5) was successfully synthesized by mechanochemical activation of Eu2O3 and alpha-Fe2O3 mixtures for 0-12 hours of ball milling time. The study is of relevance to catalysis, biomedical, sensing and energy-related applications. Fe-57 and Eu-151 Mossbauer spectroscopy were used to investigate the phase evolution, solid solution formation and hyperfine parameters of xEu(2)O(3)-(1-x)alpha-Fe2O3 nanoparticle system under the mechanochemical activation process. The Fe-57 Mossbauer studies showed that the spectrum of the ball milled samples evolved from a sextet for hematite to sextets and a doublet upon duration of the milling process with europium oxide. This indicated the formation of the EuFeO3 perovskite for large x values and long milling times. The Eu-151 Mossbauer investigations showed that the isomer shift decreased with increasing milling time for all molar concentrations employed.

Restoration of damaged bone tissue involves two traditional approaches: tissue grafting and alloplastic replacement. Recently, their limitations led to the development of tissue engineering, which uses degradable porous supports named "scaffolds". These porous structures (used both for tissue engineering and classic bone substitution applications) with customizable designs may be constructed by solid freeform fabrication (SFF) techniques. SFF uses various synthetic materials and may be adapted for creating ceramic-based scaffolds, which became popular due to increased demands for bone substitution materials. Among these materials, naturally derived ceramics are suitable candidates for bone replacement due to their resemblance with the mineral bone. Innovative optimization routes for preparing naturally derived ceramics with modulated properties implies the management of key parameters involved in heat treatment of animal hard tissues: temperature, heating environment, and cooling conditions. Both powders and bulk pieces are evaluated with complementary techniques that focus on compositional, morphological, and structural features. Finally, qualitative and quantitative biological assay in relevant cell culture of the compacted powders may assist extensive testing programs for further evaluation of different ceramic scaffolds. All these results contribute to effective assessment of ceramics tuning strategies and to subsequent modulation of their enhanced properties and long-term functionality.

In this paper, we report the structural and morphological properties of silver-doped hydroxyapatite (AgHAp) with a silver concentration x(Ag) = 0.5 before and after being thermal treated at 600 and 1000 degrees C. The results obtained by X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy suggest that the structure of the samples changes gradually, from hydroxyapatite (AgHAp_40) to a predominant beta-TCP structure (AgHAp_1000), achieved when the thermal treatment temperature is 1000 degrees C. In the AgHAp_600 sample, the presence of two phases, HAp and beta-TCP, was highlighted. Also, scanning electron microscopy studies suggest that the shape and dimension of the nanoparticles begin to change when the temperature increases. The antimicrobial activity of the obtained compounds was evaluated against Klebsiella pneumoniae, Staphylococcus aureus, and Candida albicans strains.

The effects of the bonding mechanism and band alignment in a ferroelectric (FE) BaTiO3/ferromagnetic La0.6Sr0.4MnO3 heterostructure are studied using x-ray photoelectron spectroscopy and first-principles calculations. The band lineup at the interface is determined by a combination of band bending and polarization-induced modification of core-hole screening. A Schottky barrier height for electrons of 1.22 +/- 0.17 eV is obtained in the case of downwards FE polarization of the top layer. The symmetry of the bonding states is emphasized by integrating the local density of states +/- 0.2 eV around the Fermi level, and strong dependence on the FE polarization is found: upwards, polarization stabilizes Ti t(2g) (xy) orbitals, while downwards, polarization favors Ti t(2g) (yz) symmetry. It is predicted that the abrupt (La, Sr)vertical bar TiO2 interface is magnetoelectrically active, leading to a A-type antiferromagnetic coupling of the first TiO2 interface layer with the underlying manganite layer through a superexchange mechanism.