O. de O. Damasceno

181Ta perturbed angular correlation study of hydrogen duffusion in hafnium hydride

Abstract The quadrupole coupling parameters of the 181Ta probe measured by Perturbed Angular Correlation spectroscopy in the f.c.c. phase of hafnium hydride (HfH1.64). Spin relaxation phenomena associated with the hydrogen diffusion are observed above 100°C. The activation energy deduced from the temperature dependence of the quadrupole relaxation constant is in agreement with the values previously observed by 1H NMR spectroscopy. No significant perturbation of the hydrogen diffusion due to the presence of Ta substitutional impurity is detected.

Complex impedance study of KDP protonic conductivity

Abstract The protonic conductivity in KDP (KH2PO4) pellets prepared by fusion are studied in air by complex impedance spectroscopy in the temperature range 404–471 K. Impedance spectra are plotted over a wide range of frequencies (10−2 – 106 Hz) at each sample temperature. The KDP protonic conductivity is found to obey an Arrhenius law with Ea = 0.99 eV and σ o = 6.89 × 10 5 Ω −1 cm −1 . The low frequency part of the impedance spectra tends towards a perfect 45° line typical of an interfacial diffusion process which was interpretated as being due to the migration of H species in and out the silver electrodes.

Specific conductivity of lithium perclorate dissolved in poly (ethylene glycol-400) distereate

Abstract We have measured, at different concentrations, the conductivity of lithium perclorate dissolved in poly (ethylene glycol-400) distereate. Heating-cooling cycles from 40°C to 100°C have shown reversible and reproducible data. In liquid phase the concentration-dependence of the conductivity passes through a sharp peak (1.42 × 10−4 s/cm at n=10 and T=50°C). A fitting model to this behaviour is suggested. The temperature dependence both of the conductivity and of the viscosity is shown and discussed.

Etude par correlation angulaire γ-γ perturbee des aspects statiques et dynamiques de la structure du heptafluorohafniate de sodium

Abstract We have studied the temperature dependence of the perturbation of the differential γ-γ angular correlation of the 181 Ta 133–482 keV cascade in sodium heptafluorohafnate. In the 20–300°C temperature region, we observed a drastic variation of the quadrupole interaction parameters when raising the temperature from 100 to 180°C. Such a variation is due to the existence of a phase transition corresponding to an orthorhombic-quadratic transformation of the lattice. In the low temperature phase ( T T > 180°C) the perturbation arises from the combination of static and dynamic interactions. The dynamic part of the interaction could be analysed within the isotropic perturbation model and was ascribed to jumps of the fluorine atoms onto the vertices of the cubic coordination polyhedra of the hafnium in the HfF 7 3− ion. The activation energy of the process is 0.13 ±0.03 eV. The idea of an order-disorder phenomena occuring in the course of the phase transition is consistently supported by these observations. Our results yield also valuable informations about the nature of the hafnium-fluor bond in this compound.

Disorder model for specific conductivity of lithium perchlorate dissolved in poly(ethylene glycol-400) distearate☆

Abstract Impedance Spectroscopy (IS) and Differential Scanning Calorimetry (DSC) measurements, which we have performed at different concentrations and temperatures, support a peculiar order-disorder transition model for lithium perchlorate dissolved in Poly(ethylene glycol-400) distearate systems ( LiClO 4 PEGD ). Our model has the advantage of encompassing both critical and non-critical features displayed by the specific conductivity dependence of LiClO 4 PEGD systems on concentration and temperature, respectively.

Complex impedance study of annealing effects on polycrystalline KDP conductivity

Abstract Annealing effects on the conductivity of KDP (KH 2 PO 4 ) samples prepared either by melting under slight pressure (5.7 kgf/cm 2 ) or by powder compression (1.3 × 10 3 kgf/cm 2 ) were studied in air by complex impedance spectroscopy. In both cases, annealing at 423 K reduces the conductivities to constant values: from 6.2 × 10 −6 to 1.6 × 10 −7 Ω −1 cm −1 for samples prepared by melting and from 1.9 × 10 ∼7 to 6.1 × 10 ∼8 Ω −1 cm −1 for samples prepared by compression. Heating KDP at about 500 K significantly modifies its electric properties. Two relaxation processes are observed after this treatment. One of them is associated with a fairly strong dielectric polarizability. A small conductivity jump is observed close to 440 K.

Raman scattering in complexed poly(ethylene glycol-400) distereate-lithium perchlorate systems

We have studied at room temperature, in a wide range of concentrations, complexed poly(ethylene glycol-400) distereate-lithium perchlorate systems by using micro-Raman scattering. Interactions between cations and anions and between dopant ions and host complexed polymer were observed and analyzed.

Complex impedance study of carnauba wax in liquid phase

Abstract Complex impedance study of Carnauba Wax in the liquid phase has been carried out at different temperatures. Both the specific conductivity and the relaxation frequency have presented the same activation energy, 0.295 eV. Evidence for the existence of a unique conductivity process, essentially different from polarization mechanism, are pointed out.

High-temperature system for γ-γ angular correlation experiments

The authors describe the construction and performance of a high-temperature system which was designed to work between room temperature and 1200 degrees C. It was specifically conceived for gamma - gamma angular correlation experiments but can be easily adapted to other kinds of experiments and experimental conditions. The stability of the system was found to be better than 1/1000 for a few hours and better than 2/1000 for prolonged periods.