G. Cannelli

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.

Mechanisms of the semi-insulating conversion of InP by anelastic spectroscopy

Venezia Tecnologie SpA (ENI Group), Via delle Industrie 39, I-30175 P. Marghera (VE), Italy~Received 2 December 1999!Elastic energy absorption measurements versus temperature on semiconducting, semi-insulating~SI!, andFe-doped InP are reported. A thermally activated relaxation process is found only in the SI state, which isidentified with the hopping of H atoms trapped at In vacancies. It is proposed that the presence of In vacanciesin InP prepared by the liquid encapsulated Czochralski method is due to the lowering of their energy by thesaturation of the P dangling bonds with H atoms dissolved from the capping liquid containing H

Quantum diffusion of deuterium in GaAs:Zn

Abstract The dynamics of deuterium in GaAs doped with Zn has been investigated by anelastic relaxation. The most likely configuration is D trapped by substitutional Zn, although D trapped at a Ga vacancy cannot be excluded. The relaxation of D occurs at about 20 K in the kHz range and has the highest rate found up to now for a hydrogen isotope in a semiconductor. The shape of the curves of the elastic energy loss vs temperature indicates that the nature of the D re-orientation is strongly quantistic.

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.

Reordering stages of oxygen around 500 K in ReBa2Cu3O6+x by anelastic relaxation measurements

Abstract We report new effects on the elastic energy dissipation and modulus of ReBa 2 Cu 3 O 6+ x (Re = Eu, Y) occuring around 500 K for x ≤ 0.3. The observed phenomenology is discussed in relation with the kinetics of the O ordering and with the phase diagram of ReBa 2 Cu 3 O 6+ x . The achievement of equilibrium is thought to pass through metastable states, each associated to the activation energy characteristic for dissociation of the particular species, like O pairs, isolated chain fragments or ordered domains.

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.

New low activation energy processes in La2CuO4+δ by elastic energy loss experiments

Abstract The anelastic relaxation spectrum of La 2 CuO 4+δ in the as prepared condition is measured from 200 K down to 1.3 K at frequencies included between 0.7 and 9 kHz. Two new relaxation processes are found with maxima at 4 and 70 K. The process at 70 K consists of two close peaks, with activation enthalpies of 0.11 and 0.13 eV. Possible mechanisms are thermally activated hopping of the holes doped by interstitial O, possibly bound to some lattice defect or impurity, or of atoms in off-centre positions. The peak at 4 K is, to our knowledge, by far the fastest anelastic relaxation process ever reported in an oxide superconductor. It is broader than a single relaxation process, but definitely sharper than the maxima which are typical of amorphous materials. The relaxation should again involve polarons or off-centre atoms, with a rate which is dominated by tunnelling.

Possible observation of polaron pairs in highly doped YBa2Cu3O6+x by elastic energy loss

Abstract Anelastic relaxation measurements were made on polycrystalline YBa 2 Cu 3 O 6+x with x close to 1. Among the three low-activation-energy processes which are present, that with the lowest activation enthalpy ( H ∼ 0.08 eV) is the most sensible to small variations of the O stoichiometry and becomes undetectable when x p z holes in the apical oxygens, which have been previously observed by X-ray absorption spectroscopy in highly doped YBa 2 Cu 3 O 6+x , and which are supposed to be far less mobile than the conducting holes.

Anelastic Relaxation Due to Interacting Point Defects

The anelastic relaxation is one type of mechanical response of solids in which, on applying a stress, besides the instantaneous elastic response according to Hook’s law, a retarded strain is found [1]; it is the mechanical analogue of the dielectric relaxation. However, whilst some work has been done in order to see the effect of the random interactions between dipolar impurities on dielectric relaxation, little has been done in this direction for anelastic relaxation.