Advanced Materials Forum III

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Authors: Maria Cristina Mozzati, Andréy G. Badalyan, Giulia Demaestri, Pietro Galinetto, Francesco Rossella, Veronica Bermúdez, Carlo B. Azzoni, Giorgio Samoggia
Abstract: EPR and optical absorption measurements have been performed on nearly stoichiometric lithium niobate single crystals with iron in traces and in 0.1% molar nominal amount. Thermal treatments in reducing atmosphere allowed to obtain samples with different Fe2+/Fe3+ ratios. The Fe2+/Fe3+ dynamic has been observed by irradiating the samples with UV and visible light in the temperature range 4-300 K: the photochromic effect resulted to be more evident in the strongly reduced crystals. A simple model to explain the photochromic behavior in nearly stoichiometric LiNbO3:Fe is proposed.
Authors: Luís M. Gonçalves, Carlos Couto, Pedro Alpuim, D. Michael Rowe, J. Higino Correia
Abstract: The deposition and characterization of n-type Bi2Te3 and p-type Sb2Te3 semiconductor films are reported. The films were deposited by thermal co-evaporation on a 25 µm thick polyimide (kapton) substrate. The co-evaporation method is inexpensive, simple, and reliable, when compared to other techniques that need longer time periods to prepare the starting material or require more complicated and expensive deposition equipment. Seebeck coefficients of -189 µVK-1 and +140 µVK-1 and electrical resistivities of 7.7 µ0m and 15.1 µ0m were measured at room temperature on n-type and p-type films, respectively. These values are better than those reported for films deposited by co-sputtering or electrochemical deposition, and are close to those reported for films deposited by metal-organic chemical vapour deposition or flash evaporation. Because of their high figures of merit, these films will be used for the fabrication of a micro-Peltier element, useful in temperature control and laser-cooling for telecommunications.
Authors: Eriks Klotins
Abstract: Polarization response including ergodicity breaking and the divergence of relaxation time is reproduced for model Hamiltonians of growing complexity. Systematic derivation of the dynamical equations and its solutions is based on the Fokker-Planck and imaginary time Schrödinger equation techniques with subsequent symplectic integration. Test solutions are addressed to finite size and spatially extended problems with microscopically interpretation of the model parameters as a challenge.
Authors: Alexander Deyneka, Zdenek Hubička, V.A. Trepakov, Gunnar Suchaneck, Lubomir Jastrabik, Gerald Gerlach, Jan Pokorny, Dasgmar Chvostova, J. Olejníček
Abstract: Technology aspects and characterization of BaxSr1-xTiO3 (BST) films fabricated with low pressure plasma jet technique are presented. BST films were deposited on silicon coated with Pt/TiO2/SiO2 and on bare Si substrates. The nozzles-type RF hollow cathode has been fabricated from hot pressed BaTiO3, SrTiO3, and BST ceramics. Controlling of RF voltage, RF current and substrate temperature allowed us to deposit reproducible films with controlled grain size. Hysteresis loops, ellipsometric and micro-Raman investigation results are presented and discussed.
Authors: Harvey Amorín, Andréi L. Kholkin, Maria Elisabete V. Costa
Abstract: A quantitative model for the calculation of spontaneous polarization of BLSF ceramics as a function of the degree of texture is presented using a general formalism based on the texture analysis via an orientation distribution function. The March-Dollase equation was selected to fit the measured texture distribution because its fitting parameters can be related to experimentally measurable stereological values obtained from SEM images. The results are applied to the SrBi2Ta2O9 (SBT) system, which is a well-known member of the BLSF family. The textured SBT ceramics were fabricated by templated grain growth (TGG) and the microstructure and degree of texture were evaluated by SEM analysis, which allowed correlating the texture development to the sintering parameters. Enhanced ferroelectric properties were measured perpendicularly to the uniaxial pressing direction of the ceramics, revealing the influence of the grains orientation, anisotropy and volume fraction of textured material on the ferroelectric properties. Finally, the predicted values for the spontaneous polarization as a function of the degree of texture were compared with those measured from the hysteresis loops.
Authors: Gunnar Suchaneck, Alexander Deyneka, Lubomir Jastrabik, Gerald Gerlach
Abstract: Self-polarized Pb(Ti,Zr)O3 thin films deposited under lead enriched conditions by multitarget reactive sputtering at low substrate temperatures are characterized by tetravalent B-site occupation of excess lead. The imaginary part of the dielectric constant of such films shows a relaxor-like behavior. Evidence of a Pb2+/Pb4+ mixed valence is given by the temperature and frequency dependence of the ac conductivity. PbO volatility starts to deplete the growing film at a critical temperature of 500°C and Pb4+ formation disappears.
Authors: Ai Ying Wu, Dirk Van Genechten, Paula M. Vilarinho, Marlies K. Van Bael
Abstract: In the current work two different routes, an alkoxide based sol-gel and an aqueous solution-gel route, were used to synthesize PZT (30/70) powders. The phase purity, morphology and particle size of both were studied by XRD, TEM and particle size analysis. The dispersion behavior of the powders in water was investigated by means of light scattering particle size analyzer and zeta potential measurements. The extent to which powder morphology, synthesis route and particle charge state relate to the resulting dispersion behaviour was established. Alkoxide sol-gel derived powders are better dispersed in aqueous media than aqueous solution-gel derived powders.
Authors: José A. Pérez de la Torre, Maria do Rosário Soares, Pedro Q. Mantas, Harvey Amorín, Maria Elisabete V. Costa, Ana Maria R. Senos
Abstract: To grow single crystals within the solid solutions between PbZrO3 and PbTiO3, PbZrxTi1- xO3 or PZT, is very difficult when compositions are around the morphotropic phase boundary (MPB). In this work, the PZT single crystals were grown by the high temperature solution method, using fluxes with a constant composition, different thermal profiles and different flux/PZT ratios. This approach was successful used to obtain PZT single crystals with compositions near the MPB, of 2 × 2 × 2 mm3 size and without second phases. The specific experimental conditions to obtain these crystals are analysed and discussed.
Authors: Elena Dimitriu, Floriana Craciun, Marin Cernea, Rodica Ramer
Abstract: The behaviour of the dielectric and piezoelectric properties of doped PZT ceramics, with variable lead content, has been investigated from –50oC to room temperature. The PZT materials were prepared by the oxide technique and samples were sintered as pellets, at various temperatures. Niobium and lithium ions have been substituted for Ti4+, Zr4+ in the PZT matrix, and a small amount of Bi2O3 was added to cause A-position vacancies. The lead content in the four materials prepared varies in a narrow range, from 0.97 to 1.029 lead atoms, while the concentration of all other components are maintained constant. The microstructure of samples, evaluated by SEM technique and XRD analysis evidenced the presence of the tetragonal phase characteristic for the PZT 52/48. The dielectric and piezoelectric c onstants measured on poled samples depends on the sintering temperature, defects and domain walls, lead content.
Authors: Anatoli Khodorov, M.J.M. Gomes
Abstract: Lanthanum modified lead zirconate titanate (PLZT) thin films were fabricated on indium doped tin oxide (ITO) - coated glass substrate by sol-gel method. The structure of the films was characterized with XRD and SEM. In the case of PLZT the dielectric function was modelled as a sum of Lorentzian oscillators and found by fitting the transmittance and reflectance spectra measured at normal incidence in the wavelength range of 220-2400 nm. The anomalous behaviour of dielectric function was observed below the absorption edge that was suggested to be due to formation of some defect states. The evolution of the absorption edge as well as dielectric function with film thickness was observed and discussed.

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