Influence of Cu ions on the photo-transport properties in KTaO3:(Cu,V) single crystals.

Photoconductivity kinetics, temperature dependence and excitation spectra were measured in the intervals 15-300 K and 2-4.2 eV in KTaO3:(Cu,V) single crystals processed by oxidation/reduction treatments. The kinetics, excited by band-gap excitation, present very slow saturation times, while faster time responses were observed using excitation below the band-gap. The oxidized crystal exhibited higher photoconductivity when Elight > 3 eV. Linear dependence on light intensity was measured, suggesting one center recombination processes. Optical absorption at room temperature was checked as complementary informatio

Magnetic order in TM-doped TiO2 single crystals.

Needle shaped single crystals of TM-doped rutile TiO2 (TM = Cr, Mn, Fe, Co, Ni, Cu), grown in a sodium tetraborate melt with the flux method, are analysed in their structural and optical properties with a multi-technique approach. The ferromagnetic behaviour, observed up to room temperature, overlapping the prevailing expected paramagnetism, is investigated by means of static magnetization measurements performed at different temperatures and magnetic field

The radiation-induced grafting of polybutadiene onto silica

The g-ray induced grafting of polybutadiene oligomers onto precipitated silica was investigated in the dose range up to 200kGy by THA,FTIR, CP/MASNMR, TEMmicroscopy, inverse gaschromatography (IGC), with determination of the grafting yields and the characterization of the modified silica with respect to surface energy, SiO2–oligomer interaction and morphology. The matrix EPR spectroscopy was employed for investigating the nature of the intermediate radicals in the grafting mechanism

Magnetic polaron percolation on a rutile lattice: A geometrical exploration in the limit of low density of magnetic impurities

The evolution of magnetic polaron clusters on a rutile lattice has been explored, and the results are used to discuss the origin of ferromagnetism in transition-metal (TM)-doped rutile TiO2 oxides. It is shown that percolation on a rutile lattice is characterized by a threshold different from that found for the percolation of randomly distributed spheres, which has been so far assumed as a model to treat the percolation of magnetic polarons in diluted magnetic semiconductors. Furthermore, unlike previous investigations, we explicitly considered the condition of small density n(i) of TM impurities, i.e., a regime that is quite far from that usually regarded for polaron formation, dominated by a high density n(i) of TM ions. Assuming that ferromagnetic coupling arises between polarons that share common TM impurities, we show the effect of this constraint on the magnetic properties of the sample compared to those reported for the ni n(i)>> n(h) regime

Divalent impurity ions in potassium tantalate crystals: EPR investigations.

Electron paramagnetic resonance experimental results of potassium tantalate single crystals doped by Co2+ ions as well as new results of our continuous studies of KTaO3:Cu single crystals are presented. Divalent impurity ions substitute for Ta5+ in the octahedron position in the KTO3 crystal and oxygen vacancies are required to compensate the extra charge of Ta5+. The Cu2+ ions associated with oxygen vacancies form only axial centres (included exchange coupled pair centre), the symmetry axes being along cubic directions. A new axial centre of Co2+ in the crystal of KTaO3:Co has been studie

Impurity centers and host microstructure in weakly doped SrTiO3:Mn crystals: New findings

Electron paramagnetic resonance (EPR), optical absorption and low-frequency (100 Hz - 1 MHz) dielectric permittivity investigations on Verneuil as-grown and reduced SrTiO3:Mn (0.1% at.) crystals were carried out to establish connection between the structure of Mn doping related centers and the SrTiO3 dielectric properties. At room temperature the EPR spectrum of as-grown crystals evidences isotropic Mn4+ and Mn2+ centers. The Mn2+/Mn4+ ratio increases, according to the EPR spectra, by decreasing the temperature and the signals intensity of both centers strongly decreases approaching T similar to 120 K. Such behavior is attributed to antiferromagnetic interaction in MnO and MnO2 nano-clusters. Also the dielectric permittivity behavior evidences samples inhomogeneity as well as absence of pronounced dielectric relaxation in as grown crystals. In reduced crystals the Mn2+ concentration increases and the dielectric relaxation emerges evidencing a polaronic-related nature of dipole reorientations