The Preisach model is a classical method for describing nonlinear behavior in hysteretic systems. According to this model, a hysteretic system contains a collection of simple bistable units which are characterized by an internal field and a coercive field. This set of
bistable units exhibits a statistical distribution that depends on these fields as parameters. Thus, nonlinear response depends on the specific distribution function associated with the material. This model is satisfactorily used in this work to describe the temperature-dependent ferroelectric response in PZT- and KNN-based piezoceramics. A distribution function expanded in Maclaurin series considering
only the first terms in the internal field and the coercive field is proposed. Changes in coefficient relations of a single distribution function allow us to explain the complex temperature dependence of hard piezoceramic behavior. A similar analysis based on the same form of the distribution function shows that the KNL–NTS properties soften
around its orthorhombic to tetragonal phase transition.
Ochoa, D. A.; Perez, R.A.; Garcia, J. E. Applied physics A. Materials science and processing Vol. 112, num. 4, p. 1081-1088 DOI: 10.1007/s00339-012-7492-3 Data de publicació: 2013-09 Article en revista
The alteration of the high-field electrical permittivity (nonlinear response) of PZT-based ceramics when an electrical bias field is applied is reported in this work. Large differences are observed between soft and hard PZT behaviours. While in soft PZT a bias field does not modify the nonlinear behaviour, a notable dependence is verified in hard PZT. The Preisach model is satisfactorily used to describe experimental results. A distribution function containing the first terms of the Maclaurin development series of a function composed by two Gaussian-like functions of different amplitudes is proposed. The model gives a satisfactory explanation for the fact that the permittivity depends not only on the amplitude of the applied electric field, but also on the bias field, both for soft and hard ceramics and for poled or unpoled samples.
Salvadó, N.; Butí, S.; Marine Cotte; Cinque, G.; Pradell, T. Applied physics A. Materials science and processing Vol. 111, num. 1, p. 47-57 DOI: 10.1007/s00339-012-7483-4 Data de publicació: 2013-04 Article en revista
A representative selection of green paintings from fifteenth century Catalonia and the Crown of Aragon are analyzed by a combination of synchrotron radiation microanalytical techniques including FTIR, XRD, and XRF. The green pigments themselves are found to be a mixture of copper acetates/basic copper acetates and basic copper chlorides. Nevertheless, a broader range of green shades were obtained by mixing the green pigment with yellow, white, and blue pigments and applied forming a sequence of micrometric layers. Besides the nature of the pigments themselves, degradation and reaction products, such as carboxylates, formates and oxalates were also identified. Some of the copper based compounds, such as the basic copper chloride, may be either part of the original pigment or a weathering product. The high resolution, high brilliance, and small footprint of synchrotron radiation proved to be essential for the analysis of those submillimetric paint layers made of a large variety of compounds heterogeneous in nature and distribution and present in extremely low concentrations.
Pradell, T.; Molera, J.; Salvadó, N.; Labrador, A. Applied physics A. Materials science and processing Vol. 99, num. 2, p. 407-417 DOI: 10.1007/s00339-010-5639-7 Data de publicació: 2010-05 Article en revista
Macanás, J.; Palacio , L.; Prádanos, P.; Hernández, A.; Muñoz, M. Applied physics A. Materials science and processing Vol. 84, num. 3, p. 277-284 DOI: 10.1007/s00339-006-3609-x Data de publicació: 2006 Article en revista
Activated composite membranes (ACM) have been made based on a polysulfone layer over a non-woven support with a dense layer of aromatic polyamide, and deposited on the polysulfone using interfacial polymerisation by a carrier agent – di(2-ethylhexyl) dithiophosphoric acid – added to the membranes at several concentrations. Two polysulfone supports have been used, one of them commercial (PSf-Com) an other made ad hoc by us (PSf-GTS).
The membrane structure has been characterised by both atomic force microscopy (AFM) and scanning electron microscopy (SEM). Firstly, the two polysulfonic bases were studied. The results show that structurally both are quite similar. PSf-Com presents a more regular sponge like structure in the bulk with some macrovoids randomly distributed, with an average size of 25 µm.
The results obtained demonstrate that after interfacial polymerisation, some structural defects appear with relatively big valleys and peaks. The roughness has been studied versus the AFM scan size, which allowed the evaluation of the corresponding fractal dimensions. This permitted a detailed comparison and detection of the differences and similarities of the surface structure of all the membranes studied.
The membranes made on PSf-GTS, whose surface structure seems to yield a better coverage of polyamide, gave good performances in the extraction of certain heavy metals. After extraction the membranes were analysed by EDS to confirm the permanence of the extractant along with some deposits of salt and extracted ions.
Pérez-Arantegui, J.; Larrea, A.; Molera, J.; Pradell, T.; Vendrell-Saz, M. Applied physics A. Materials science and processing Vol. 79, num. 2, p. 235-239 Data de publicació: 2004-07 Article en revista