R. Cantelli

Glass transition temperature of water confined in lipid membranes as determined by anelastic spectroscopy

The research of gene delivery vehicles used in gene therapy is focused on nonviral vectors like lipid membranes. Such vectors, nonimmunogenic and biodegradable, are formed by complexation of DNA with a mixture of cationic lipids and a neutral colipid which improve the transfection efficiency. A main topic related to lipid membrane dynamics is their capability to spontaneously confine water. At present the value of the glass transition temperature (Tg) is largely debated and determined only by some indirect methods. Here the authors show that anelastic spectroscopy allows the confined water Tg value to be directly identified in several lipid mixtures.

Fast oxygen mobility in tetragonal YBa2Cu3O7-x by anelastic relaxation measurements

Abstract Evidence of a very high mobility of the isolated O atoms in the Cu(1)-O basal planes of tetragonal YBa2Cu3O6.2 is reported. The jumps of the isolated O atoms between the O(4) and O(5) positions are expected to give rise to a well detectable anelastic relaxation process, and a recently reported elastic energy dissipation peak in YBa2Cu3O6.2 (63 K, 1.1 kHz) was attributed to this mechanism, resulting in an O diffusion coefficient in the basal plane of 4 × 10 −4 exp (−0.11 eV kT ) cm2/sec. Measurements are produced here which show that all anelastic processes above room temperature in orthorhombic YBa2Cu3O7-x disappear in YBa2Cu3O6.2, confirming that the low temperature peak is indeed due to the diffusion of the free oxygen.

An internal friction and frequency study in YBa2Cu3O7−x

Abstract Measurements of anelastic relaxation in the kHz range have been conducted in YBa 2 Cu 3 O 7−x between 300 and 60 K. Two peaks are observed around the superconducting transition temperature, at 110 K and just below T c , and an additional maximum at - 160 K in the sample prepared with BaCO 3 . The previously reported phase transformation at T t - 240 K is shown to give rise to hysteretic effects which are absent when thermal cycling is conducted above T t . The possible relation of the presently studied phase transformation with the non-reproducible enhancement of T c above 100 K is discussed.

Oxygen ordering and mobility in ReBa2Cu3O6+x by elastic energy loss and modulus measurements

Abstract It is reported on new anelastic relaxation measurements in ReBa 2 Cu 3 O 6+x for 0 x planes in the various phases is discussed, and the two thermally activated peaks of elastic energy dissipation observed above room temperature are interpreted in that framework. A new structural phase transition around 480 K is observed.

Metal to semiconductor transition of vacuum annealed YBa2Cu3O7-x and characterization of its semiconducting state

Abstract Electrical resistance measurements have been conducted in YBa2Cu3O7-x in the temperature range 80–350 K before and after the metal to semiconductor-like transition induced by vacuum annealings at 570 and 640°C. In the semiconducting phase (7 - x = 6.2 ± 0.2), the temperature dependence of resistivity closely follows the exponential law of classical semiconductors with an energy gap Eg = 0.77 eV.

Tunneling of H and D in Metals and Semiconductors

Due to their low mass, interstitial H and its isotopes may exhibit marked quantum effects in solids. These appear both as coherent delocalization of the H wave function over two or more interstitial sites, and as a mobility that is not described by the classical Arrhenius law. The earliest and most extensive investigations have been carried out in bcc metals, notably in Nb and Ta and recently in the hcp rare earths Y and Sc. Quantum effects in f cc metals are found to be less marked, and a coherent tunneling system (TS) of H has never been found, possibly because in these lattices, the distance between the interstitial sites occupied by H is greater than in bcc metals, hence reducing the overlap between the H wave functions in adjacent sites.

Local Structure and Dynamic Properties of Mn Substituted Manganites Studied by EXAFS and Anelastic Spectroscopy

We present extended X-ray absorption fine structure (EXAFS) and anelastic spectroscopy measurements performed on (La0.63Ca0.37)(Mn1-yMy)O3 manganites (M = Cr or Ni and y = 0.03, 0.08). The ferromagnetic metallic phase maintains its long-range character even after Mn substitution with non- Jahn-Teller ions, but both the doping species (Ni or Cr) lower the Curie temperature and broaden the magnetic transition. EXAFS suggests the presence of distorted insulating zones in the framework of phase inhomogeneity. Moreover, a strong dependence of the real part of the complex dynamic Young’s modulus and of the elastic energy-loss coefficient on the Mn substitution is evidenced by the anelastic spectroscopy spectra. These results confirm the correlation among local lattice disorder, dynamic and magnetic degrees of freedom and also evidence the possibility to tune manganites physical properties acting on their chemical composition.

Hydrogen four-level tunnel systems in substitutional body-centred cubic alloys

Abstract A brief account is provided of the main results of a study of the tunneling states of H trapped by substitutional (S) impurities in Nb, mainly consisting in anelasticity experiments. The p...