Variations of internal friction in YBa 2 Cu 3 O x superconductors (original) (raw)

Low temperature internal friction spectrum of YBa2Cu3Ox

Physica C: Superconductivity, 1991

The elastic and anelastic behaviours of polycrystalline YBazCu90, specimens have been studied between 80 and 300 K, by means of a resonant bar technique. Three damping peaks have been observed at 90, 115 and 220 K. The stability of these peaks during annealing in vacuum has been carefully examined. The 90 K peak is not related to the superconducting transition because it is still observed after thermal treatments leading to the disappearance of superconductivity. The 115 K is due to a relaxation mechanism. The activation energy is-0.17 eV and the frequency factor is-10" s-'. Also this peak is certainly correlated with the excess oxygen atoms, because it disappears with annealing in vacuum. The 220 K maximum, which was also observed by ultrasonic measurements, seems to be affected by the sample preparation, i.e. by the sintering conditions. Finally, a frequency hysteresis has been observed in every superconducting sample, which accounts for an anomalous behaviour of the elastic modulus.

Thermal stability of superconducting YBa2Cu3O9-x in different environments

The controlled atmosphere the~ogravimet~c analysis carried out on the supercondu~tiug YBa2Cu@6.9s phase shows the transformation of an orthorhombic I (0,) to On phase over the stoichiometric range 6.79 ( IO33 K) and 6.68 ( 1 I73 K) in oxygen, followed by a narrow range of single phase On. The On phase then goes to the tetragonal phase (T). In the On/T phase boundary the relationship log poI =68.9-8.252 x 104/T is found to hold. The stoichiometric limit of the tetragonal phase and the On/T phase boundary are discussed.

The Internal Friction Peaks in YBa 2 Cu 3 O 6+x Above Room temperature Mark the Phase Transformations of the System

Le Journal de Physique IV, 1996

the YBa2Cu306+, system exhibits internal friction peaks above room temperature. These peaks are thermally activated. When the system is fully oxygenated (x=l), one peak only is detected. At a lower oxygen content, x<0.8, this peak change in shape and position and a new one can be contemporarily detected. These peaks are reasonably linked with the crystal phases of the system. We present a sequence of measures taken on the same sample, where the evolution of these peaks is shown.

Off-stoichiometric superconducting phases, oxygen mobility and anelastic relaxation in YBa2Cu3O7−x

Physica C-superconductivity and Its Applications, 1992

Elastic energy dissipation measurements were carried out using the vibrating reed and torsional pendulum techniques on polycrystalline YBa2Cu3Ov_x specimens in different stoichiometric conditions. In the 300-900 K range two relaxational damping peaks, Po~ and Poz, can be observed. The relaxation strength depends considerably on the oxygen deficiency x. As the value of x increases, the intensity of peak PoJ decreases while that of Po2 increases. The two relaxation processes have activation energies H~ = (1.54 + 0.09) eV and//2 = (1.3 _+ 0.1) eV, respectively. Models for the relaxation involving the dynamics of oxygen atoms in the Cu-O basal plane and along the twinned interfaces are examined.

Split superconducting transitions in the specific heat and magnetic susceptibility of YBa2Cu3Ox versus oxygen content

Physica C: Superconductivity, 1993

A homogeneous batch of YBasCusO, porous ceramics was studied in detail as a function of the annealing temperature T,. Xray diffraction patterns and optical micrographs show definitely one single phase. Well-separated double superconducting transitions are, however, observed; most clearly in the specific heat curves, except for T,-460°C. Initial values are T,, = 87 K and T,,=92 K for T,=3OO"C. Upon increasing the annealing temperature T, to SOO"C, T,, increases to 93.5 K while T,, remains almost constant. Beyond T,= 5OO"C, both T,, and T, decrease. The essentially reversible splitting of the superconducting transition appears to be due to the complex kinetics of the oxygen uptake. The two critical temperatures T, and T,, are attributed to the high oxygen content external layer of the grains and to the low oxygen content grain cores, respectively.

Low temperature internal friction spectrum of calcium doped polycrystalline YBa2Cu3O6+x

Solid State Communications, 1994

Internal friction measurements (IF) in the kilohertz frequency range were performed on Ca doped polycrystalline YBa2CugOrj+x. The samples were also characterized by DC electrical resistivity and X-ray measurements. The IF spectra obtained in the present investigation show an increase in the low temperature mechanical loss maxima at 95 K and 115 K with increasing Ca content. This could be interpreted as being due to an increase in the electrical charge density, the Yk-ions being replaced by the lower valent CaZ+-ions, thus creating additional holes. Furthermore the fact that doping increases the electrical charge density is shown by a decrease in the electrical resistivity with increasing Ca content. Thus the low temperature IF peaks could be attributed to the hopping of electronic defects in the Cue;! planes and in the CuO chains, whose density increase with Ca content.