High temperature piezoelectric properties of flux-grown α-GeO 2 single crystal

International audienceThe temperature-dependence of the piezoelectric properties of trigonal -GeO2 single-crystals obtained by the high-temperature flux method was measured by the resonance technique of the electrical impedance in the 20°C-600°C range. To approach the values of the two independent piezoelectric coefficients d11 and d14, we first measured as a function of temperature the elastic coefficients S11, S14 and S66 and the dielectric permittivity 11 which are involved in the coupling coefficient k of both the thickness shear mode and the transverse mode. A Y-cut plate with a simple +45°-rotation ((YXtwl) +45°/0°/0°) was used to measure the coupling coefficient of the thickness shear mode, and two X-turned plates ((XYtwl) +45°/0°/0° and (XYtwl)-45°/0°/0°) were prepared to characterize the coupling coefficient of two transverse modes. From the whole experimental measurements, the piezoelectric coefficients of -GeO2 were calculated up to 600 °C. They show that this crystal is one of the most efficient in regard of the -quartz-like family at room temperature, and that its thermal comportment retains large piezoelectric properties up to 600°C

Propriétés diélectriques et piézoélectriques de céramiques de Pb(Mg1/3_{1/3}Nb2/3_{2/3}O3_{3} – PbTiO3_{3} dopées

0.65 Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$ – 0.35 PbTiO$_{3}$ ceramics doped with lanthanum, iron and manganese oxides were synthesized. Experimental results showed the dopants by creating some points defects in the network of PMN-PT act on the microstructural development of ceramics and as a result on to dielectric constant and losses values. Moreover when the Mn$^{+4}$ ion were used as a dopant in a B site of the network, dielectrics losses were notably decreased allowing some using of this material in the field of acoustic wave at reasonable power.Différentes céramiques de composition 0,65 Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$ – 0,35 PbTiO$_{3}$ (PMN-PT) dopées avec des oxydes de lanthane, de fer et de manganèse ont été synthétisées sous forme de composés massifs. Il ressort de cette étude que les dopants, en introduisant des défauts ponctuels dans le réseau, agissent sur la microstructure des céramiques et conditionnent ainsi les valeurs de la constante diélectrique et des pertes. L'ion Manganèse Mn$^{4+}$ en substitution dans les sites B de la structure des PMN-PT (35 % PT) permet d'abaisser de manière importante les pertes diélectriques du matériau, ce qui pourrait permettre d'utiliser cette céramique pour des applications de moyenne puissance

Influence des paramètres de dépôt sur la morphologie de films minces de tétraborate de lithium obtenus par le procédé “PYROSOL"

Li$_2$B$_4$O$_7$ piezo-electric thin films were prepared by “PYROSOL" process which is a useful method for the elaboration of thin films. Morphological development and crystallization of thin films are very dependent on the experimental parameters like the substrate temperature, the concentration and the relative proportion of the precursors in methyl alcohol. The effect of these various parameters were studied in order to obtain homogeneous, crystallized and oriented thin films.La réalisation de couches minces de matériaux piézo-électriques de Li$_2$B$_4$O$_7$ par le procédé “PYROSOL" révèle une grande diversité de conditions de dépôt. La température du substrat, la composition des solutions de précurseurs et leur concentration conditionnent la morphologie et l'état de cristallisation des films. En particulier, l'obtention de couches minces denses, homogènes et présentant une orientation préférentielle nécessite des températures de substrat supérieures à 620 $^{\circ}$C. L'influence de ces divers paramètres expérimentaux a été étudiée dans le but d'obtenir des dépôts homogènes, cristallisés et orientés

High-pressure structural and vibrational study of Sr Ti 0.60 Zr 0.40 O 3

International audienceWe have experimentally investigated the phase transition induced by pressure in SrTi 0.6 Zr 0.4 O 3 (STZ) by means of Raman spectroscopy and X-ray diffraction on homemade polycrystalline sample. The decrease in the number of Raman bands as the pressure increases and the discontinuity of the unit cell volume with pressure revealed a structural transition of STZ at approximately 5.5 GPa. Moreover, the X-ray diffraction data allowed us to determine the bulk moduli of the low and high-pressure phases of STZ

P(VDF-TrFE) copolymer thin films for pyroelectric applications

International audienc

The main features of GaPO4_{\bf 4} hydrothermal crystal growth under conditions of direct and retrograde solubility

GaPO$_{4}$ recrystallisation was studied under hydrothermal conditions at temperatures from 140 to 310$^{\circ}$C (autogeneous pressures from 2 to 150 bar). The acidic solvents of pH 4 to 0 at ambient conditions were used as mineralizers. The retrograde solubility of GaPO$_{4}$ was observed under 260$^{\circ}$C (pressure up to 20 bar) and direct – above 280$^{\circ}$C (pressure above 50 bar). Low values of the initial solvent pH on GaPO$_{4}$ solubility at temperatures up to 260$^{\circ}$C have an influence to increase GaPO$_{4}$ solubility and in the same time decrease crystalline quality, for example, rise of OH content is observed. Some solvents with pH near to 4 tested as mineralizers exhibit low solubility of GaPO$_{4}$,$_{}$ but increasing value at temperatures above 280$^{\circ}$C and lead to an attractive crystal growth. So, a possible explication of this phenomenon is a formation of few stable phases from an initial solution which can participate or no in reactions with GaPO$_{4}$ at certain T-P conditions.
The study of crystalline quality and physical properties as well piezoelectric of GaPO$_{4}$ single crystals have shown a significant superiority of crystals obtained at temperatures above 280$^{\circ}$C (pressures above 50 bar)

Interdigitated back contact solar cells with SiO2 and SiN back surface passivation

International audienceThe results presented in this paper concern the study of interdigitated back contact solar cells (IBC SC) emitter passivation by means of comparison of full and point contact solar cells and two type of passiv-ation layers (SiN and SiO 2) as well as different values of the emitter sheet resistance. The fabrication of contacts in the form of points does not influence significantly the I-V characteristic parameters in comparison to full contact cells for highly doped emitters, however, improvement of R sh is observed for a few point contact solar cells. A similar effect has been observed on higher sheet resistance emitters as well as a strong degradation of the dark current after the last annealing of the cell. We have attributed this effect to the short-circuiting of a too thin emitter

Acetaminophen metabolism after major surgery: a greater challenge with increasing age

International audiencePatients undergoing major surgery represent a good model for the study of the hepatic metabolism of acetaminophen (APAP) after surgery and for the evaluation of how the detoxification process is influenced by aging. Thirty patients received intravenous APAP (1 g/6 h) for 4 days (D1–D4). Daily 24-h urinary metabolites—cysteine–APAP, mercapturate–APAP, APAP, and glucuronide and sulfate conjugates—as well as blood glutathione levels were compared with repeated-measures analysis of variance (significance, P < 0.05). Between D1 and D4, cysteine–APAP increased (308 ± 308 mg vs. 570 ± 512 mg, P = 0.005), and sulfate and glucuronide conjugates decreased (1,365 ± 1,084 mg vs. 694 ± 600 mg, P < 0.0001 and 2,418 ± 817 mg vs. 1,513 ± 1,076 mg, P = 0.011, respectively). Blood glutathione decreased (790 ± 125 vs. 623 ± 132 µmol/l, P < 0.0001. These changes increased with aging. APAP disposition after major surgery shifts toward the oxidative pathways of metabolism, and this is enhanced with aging. Supplementation with sulfur-containing amino acids should be investigated further as it might minimize the effect on antioxidant defenses, especially in older persons undergoing more extensive surgical procedures