Pressure-induced phase transitions in Zr-rich PbZr1-xTixO3 ceramics

A Raman study of structural changes in the Zr-rich PbZr1-x TixO3 (PZT) system under hydrostatic pressures up to 5.0 GPa is presented. We observe that externally applied pressure induces several phase transitions in PZT ceramics among phases with orthorhombic (Ao), rhombohedral low-temperature (RLT), and rhombohedral high-temperature (RHT) symmetries (all found in PZT at ambient pressure and room temperature). Each of the compositions investigated (0.02 ≤ x ≤ 0.14) exhibits a high-pressure phase with orthorhombic (OI′) symmetry. We further report a detailed study of the pressure dependence of Raman frequencies to elucidate the phase transitions and to provide a set of pressure coefficients for the high-pressure phases.

Crystallographic structure of Ti-6Al-4V, Ti-HP and Ti-CP under high-pressure

The phase stability of a commercial purity (Ti-CP), high purity (Ti-HP) and Ti-6Al-4V alloy were investigated in a diamond anvil cell up to 32 GPa and 298 K using a polychromatic X-ray beam. The Ti-CP and Ti-HP shown the same HCP (c/a∼0.632) to Hexagonal (c/a∼1.63) non reversible martensitic transition at about 9 GPa. The as received Ti-6Al-4V shows a very low relative volume fraction β-Ti / α-Ti. No phase changes were observed in the Ti-6Al-4V alloy in the pressure range of this study. The α phase of the Ti-6Al-4V shows monotonic volume cell pressure dependence. This volume change is reversible and non-hysteretic. The cell of the a phase recovered its original volume when the pressure was released. © 2010 IOP Publishing Ltd.

A new approach to the experimental determination of the critical temperature of metamagnets

A new approach to the experimental determination of the critical temperature of metamagnetic samples with non-zero demagnetizing factors is presented. The method is applied to metamagnetic Ni(NO3)2·2H2O, allowing the conclusion that this salt exhibits a tricritical point. Pressure dependence of the critical temperature, and the existence of a pressure-induced metamagnetic transition are also reported. © 1986.

Investigação da temperatura eletrônica da fase plasma e estudo da morfologia, estrutura molecular e crescimento do polímero proveniente de um plasma de benzeno excitado por tensão contínua

Pós-graduação em Física - FEG

Estudo de propriedades elétricas em sistemas orgânicos e inorgânicos correlacionados

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Magnetoelastic couplings in the distorted diamond-chain compound azurite

We present results of ultrasonic measurements on a single crystal of the distorted diamond-chain compound azurite Cu-3(CO3)(2)(OH)(2). Pronounced elastic anomalies are observed in the temperature dependence of the longitudinal elastic mode c(22) which can be assigned to the relevant magnetic interactions in the system and their couplings to the lattice degrees of freedom. From a semiquantitative analysis of the magnetic contribution to c(22) the magnetoelastic coupling G = partial derivative J(2)/partial derivative epsilon(b) can be estimated, where J(2) is the intradimer coupling constant and epsilon(b) the strain along the intrachain b axis. We find an exceptionally large coupling constant of | G| similar to 3650 K highlighting an extraordinarily strong sensitivity of J(2) against changes of the b-axis lattice parameter. These results are complemented by measurements of the hydrostatic pressure dependence of J2 by means of thermal expansion and magnetic susceptibility measurements performed both at ambient and finite hydrostatic pressure. We propose that a structural peculiarity of this compound, in which Cu2O6 dimer units are incorporated in an unusually stretched manner, is responsible for the anomalously large magnetoelastic coupling.

Estimation of lower flammability limits of C-H compounds in air at atmospheric pressure, evaluation of temperature dependence and diluent effect

Estimation of the lower flammability limits of C-H compounds at 25 degrees C and 1 atm; at moderate temperatures and in presence of diluent was the objective of this study. A set of 120 degrees C H compounds was divided into a correlation set and a prediction set of 60 compounds each. The absolute average relative error for the total set was 7.89%; for the correlation set, it was 6.09%; and for the prediction set it was 9.68%. However, it was shown that by considering different sources of experimental data the values were reduced to 6.5% for the prediction set and to 6.29% for the total set. The method showed consistency with Le Chatelier's law for binary mixtures of C H compounds. When tested for a temperature range from 5 degrees C to 100 degrees C , the absolute average relative errors were 2.41% for methane; 4.78% for propane; 0.29% for iso-butane and 3.86% for propylene. When nitrogen was added, the absolute average relative errors were 2.48% for methane; 5.13% for propane; 0.11% for iso-butane and 0.15% for propylene. When carbon dioxide was added, the absolute relative errors were 1.80% for methane; 5.38% for propane; 0.86% for iso-butane and 1.06% for propylene. (C) 2014 Elsevier B.V. All rights reserved.

Dependence of the electrical conductivity and elastomeric properties on sample preparation of blends of polyaniline and natural rubber

Blend films (free-standing) containing 20% in volume of polyaniline (PANI) in 80% of natural rubber (NR) were fabricated by casting in three different ways: (1) adding PANI-EB (emeraldine base) dissolved in N-methyl-2-pyrrolidone (NMP) to the latex (NRL), (2) adding PANI-EB dissolved in in-cresol to NR dissolved in xylol (NRD), (3) overlaying the surface of a pure NR cast film with a PANI layer grown by in situ polymerization (NRO). All the films were immersed into HCl solution to achieve the primary doping (protonation) of PANI before the characterization. The main goal here was to investigate the elastomeric and electrical conductivity properties for each blend, which may be applied as pressure and deformation sensors in the future. The characterization was carried out by optical microscopy, dc conductivity, vibrational spectroscopy (infrared absorption and Raman scattering), thermogravimetry analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and tensile stress-strain curves. The results suggest that the NRL blend is the most suitable in terms of mechanical and electrical properties required for applications in pressure and deformation sensors: a gain of conductivity without losing the elastomeric property of the rubber. (c) 2005 Wiley Periodicals, Inc.