Nanograined Ferroelectric Ceramics Prepared by High-Pressure Densification Technique

For the first time, nanograined Pb(1-1.5x)La(x)TiO(3) ferroelectric ceramics, with x=0.2, were produced by a process based on a high-pressure densification technique (HPD) that eliminates the need of high-temperature sintering. Our results showed the production of workable dense ceramics with average grain size around 100 nm and free from secondary phase. Regarding the dielectric measurements, the samples showed satisfactory dielectric losses as well as remarkable diffusivity in the dielectric curves. Moreover, ferroelectric hysteresis measurements showed that samples produced by the HPD technique can stand high electric fields necessary to switch the polarization and thus to induce piezoelectric activity. Our results demonstrated clearly the viability of the proposed method to produce nanograined ferroelectric bulk ceramics, then opening the possibility of developing new technologies.

Dithiocarbazate complexes with the [M(PPh(3))](2+) (M=Pd or Pt) moiety Synthesis, characterization and anti-Tripanosoma cruzi activity

New neutral Pd(II) and Pt(II) complexes of the type [M(L)(PPh(3))] (M Pd or Pt) were prepared in crystalline form in high-yield synthesis with the S-benzyldithiocarbazates and S-4-nitrobenzyldithiocarbazates derivatives from 2-hydroxyacetophenone, H(2)L(1a) and H(2)L(1b), and benzoylacetone, H(2)L(2a) and H(2)L(2b). The new complexes [Pt(L(1a))(PPh(3))] (1), [Pd(L(1a))(PPh(3))] (2), [Pt(L(1b))(PPh(3))] (3), [Pd(L(1b))(PPh(3))] (4), [Pt(L(2a))(PPh(3))] (5), [Pd(L(2a))(PPh(3))] (6), [Pt(L(2b))(PPh(3))] (7) and [Pd(L(2b))(PPh(3))] (8) were characterized on the basis of elemental analysis, conductivity measurements, UV-visible, IR, electrospray ionization mass spectrometry (ESI-MS), NMR ((1)H and (31)P) and by X-ray diffraction studies. The studies showed that differently from what was observed for the H(2)L(1a) and H(2)L(1b) ligands, H(2)L(2a) and H(2)L(2b) assume cyclic forms as 5-hydroxypyrazolinic. Upon coordination, H2L2a and H2L2b suffer ring-opening reaction, coordinating in the same manner as H(2)L(1a) and H(2)L(1b), deprotonated and in O,N,S-tridentate mode to the (MPPh(3))(2+) moiety. All complexes show a quite similar planar fourfold environment around the M(II) center. Furthermore, these complexes exhibited biological activity on extra and intracellular forms of Trypanosoma cruzi in a time- and concentration-dependent manner with IC(50) values ranging from 7.8 to 18.7 mu M, while the ligand H(2)L(2a) presented a trypanocidal activity on trypomastigote form better than the standard drug benznidazole. (C) 2010 Elsevier Inc. All rights reserved.

High T/P evolution and metamorphic ages of the migmatitic basement of northern Sierras Pampeanas, Argentina: Characterization of a mid-crustal segment of the Famatinian belt

New petrologic, thermobarometric and U-Pb monazite geochronologic information allowed to resolve the metamorphic evolution of a high temperature mid-crustal segment of an ancient subduction-related orogen. The EI Portezuelo Metamorphic-Igneous Complex, in the northern Sierras Pampeanas, is mainly composed of migmatites that evolved from amphibolite to granulite metamorphic facies, reaching thermal peak conditions of 670-820 degrees C and 4.5-5.3 kbar. The petrographic study combined with conventional and pseudosection thermobarometry led to deducing a short prograde metamorphic evolution within migmatite blocks. The garnet-absent migmatites represent amphibolite-facies rocks, whereas the cordierite-garnet-K-feldspar-sillimanite migmatites represent higher metamorphic grade rocks. U-Pb geochronology on monazite grains within leucosome record the time of migmatization between approximate to 477 and 470 Ma. Thus, the El Portezuelo Metamorphic-Igneous Complex is an example of exhumed Early Ordovician anatectic middle crust of the Famatinian mobile belt. Homogeneous exposure of similar paleo-depths throughout the Famatinian back-arc and isobaric cooling paths suggest slow exhumation and consequent longstanding crustal residence at high temperatures. High thermal gradients uniformly distributed in the Famatinian back-arc can be explained by shallow convection of a low-viscosity asthenosphere promoted by subducting-slab dehydration. (C) 2011 Elsevier Ltd. All rights reserved.