M.P. Fontana

Collective vibrational modes in strong electrolyte solutions at high concentrations

Abstract We report evidence for the existence of solute related collective vibrational modes in strong II-I electrolyte solutions at high concentrations both in H2O and D2O. The evidence was obtained by studying the polarized Raman spectra of solutions of CdCl2 and NiCl2 Checks were also performed by taking the Raman spectra of the relative hydrated salts. Our results are explained in terms of vibrational densities of states corresponding to collective vibrational modes in a solute connected middle range lattice.

Temperature dependence of resistivity in YBa2Cu3O7−δ: Study of the effect of oxygen content and of paraconductivity

Abstract In this paper we report new results on the temperature dependence of the resistivity in YBa2Cu3O7−δ pellets, in which the oxygen content was controlled (0

Diffusional and vibrational dynamics of ZnCl2 aqueous solutions by inelastic neutron scattering

Abstract We have studied saturated solutions of ZnCl 2 (and NiCl 2 ) in D 2 O by time-of-flight quasi-elastic and inelastic neutron scattering spectroscopy. Spectra were taken at room temperature as a function of transferred momentum. We find that ionic diffusion in these solutions is best described by a crystal vacancy diffusion model. We also find evidence of collective excitations in the region of ∼ 20 meV.

Temperature effects on the local structure of CuBr2 aqueous solutions by EXAFS

Abstract The results of extended X-rays absorption fine structure of the ionic system copper bromide in H 2 O is reported. The measurements, performed at Adone (PULS facility) as a function of the temperature in the thermodynamical range (−20 to + 80°C) allows us to study the evolution of the nearby hydration shell around the Cu 2+ ion, and a cooperative charge is quantitatively analyzed.

Effect of hyperfine — Structure interaction in the emission of KI:Tl

Abstract It is suggested that the hyperfine interaction plays an important role in determining the radiative lifetime or the slow component of the A X emission in KI:Tl. A theoretical estimate of such decay time shows very good agreement with experiment. Previous arguments, discarding the hyperfine interaction mechanism, are discussed.

Small angle neutron scattering and structural properties in electrolytic solutions

Abstract A new direct indication concerning the structural properties of liquid systems is obtained for the first time. Small angle neutron scattering (SANS) measurements have been performed on solutions of ZnCl2, NiCl2, CuBr2 in D2O and in non aqueous solvent (EtOAc). The spectra, taken at room temperature, as a function of concentration, in the range 0.019 ⩽ K ⩽ 0.25 ( A −1 ) show in aqueous solvent an “abnormal” k-dependent small angle coherent cross section. This anomalous contribution clearly indicates the existence in the systems of correlated regions (∼ 30 A) perhaps connected through a preferred distance of ∼ 50 A. Also in pure water the results seem to indicate the existence of correlated regions of finite size.

Evidence of fractal behaviour

Abstract Low-frequency Raman scattering measurements on (AgI) x (Ag2O.B2O3), 1-x superionic glasses, as a function of the concentration of silver iodide, are reported. By using a fractal description, the crossover frequency a., in the vibrational density of states is calculated, from which is established the fractal characteristic length L. This length increases with increasing AgI concentration from ∼ 20 to ∼ 30 A.

Vibrational spectroscopy of aqueous solutions at high concentrations: Raman and inelastic neutron scattering

Abstract We review work performed by our group on vibrational spectroscopy of water and aqueous solutions of strong II-I electrolytes at high concentrations. Evidence shall be presented for the existence of intermediate range, solute-connected, ordered patches, whose collective vibrational modes yield a continuous vibrational density of states, as in amorphous solids. We shall review Raman and inelastic neutron scattering results, obtained for electrolytes such as ZnCl 2 , NiCl 2 , CuBr 2 , CdCl 2 . Other results, such as EXAFS, viscosity and ultrasonic attenuation will also be discussed.

Quasi-elastic neutron scattering investigation of molecular dynamics in EBBA nematic phase

Abstract We present data on the temperature dependence of quasi-elastic neutron scattering in a liquid crystalline aligned nematic phase. We were able to identify and separate the translational and rotational (spinning) contributions. The rotational part shows an anomalous temperature dependence, confirming earlier data taken by fluctuation IR and Raman spectroscopy.

Fano interference between the E2 (17 cm−1) optical mode and one-phonon continuum scattering from β-AgI

Abstract Resonant interference between the E2 (17 cm−1) optical mode and the continuum of one-phonon partial density of states has been observed in β-AgI, and has been shown to follow Fano formalism. The temperature dependence of the coupling parameter q shows a substantial variation as T approaches Tc. A qualitative explanation of such behaviour is made in terms of phonon assisted activation of Frenkel defects, which increases more rapidly as the superionic transition temperature is approached.