Elastic properties of polycrystalline YBa2Cu3O7−δ: Evidence for granularity induced martensitic behavior (original) (raw)
Related papers
2005
In this work we present the study of the elastic properties of polycrystalline samples of superconducting YBa 2 Cu 3 O 7-δ prepared by the sol-gel method. The quality of all samples was checked by x-ray diffraction and scanning electronic microscopy while their physical properties were verified by transport and magnetic measurements. The elastic study was performed using the standard pulse-echo technique through measuring the phase velocity and the attenuation of ultrasonic waves (in the range of a few MHz) as a function of temperature. We have focused this study on the low temperatures interval (T < 200K). The obtained results show a strong hysteretic behavior in the ultrasonic attenuation (in addition to usually observed hysteretic behavior for the velocity) which strongly supports the existence of a martensiticlike phase above the superconducting critical temperature T C. We argue that this peculiar behavior can be attributed to the granularity present in the samples.
Anisotropy of Elastic and Relaxation Properties of the Superconducting 123-YBCO Single Crystal
Le Journal de Physique IV, 1996
Acoustic properties of the YBazCu306.7 sjngle rystal are studied in the temperature range 5-300 K. The wave vector of the longitudinal and torsional/Standing waves in the frequency range 50-90 kHz was diwcted along and normal to the c-axis. It is showm that the acoustic anomalies observed in the single crystal qualitatively are the same that those found earper in t h k l 2 3-~~~0 ceramics but depend strongly on the mutual orientation of the wave vector and the c-&xis. It is1established that the significant temperature hysteresis and "softening" of the dynamic elastic moduli at thermocycling are observed only in the case when the sound waves have a displacement component along the c-axis. Moreover, in this case the sound absorption peak near 230 K is more pronounced. The locations ofjsound absorption peaks are not sensitive to the oscillation mode and sample orientation. The results obtaiqed are qualitatively consistent with the model of bistable behaviour of the sublattice formed by apical oxygkn .atoms.
Ultrasonic velocity anomalies in superconducting sinter-forgedYBa2Cu3O7−δ
Physical Review B, 1989
The velocity of ultrasound was measured on sinter-forged polycrystalline YBa2Cu307-& samples with a superconducting transition temperature of 91 K. The forging process results in crystallites which are preferentially aligned with their c axis aligned parallel to the forging axis as confirmed from optical and x-ray measurements. Sound-velocity measurements show that the material is elastically anisotropic. The temperature dependence
Elastic properties of superconducting and non-superconducting DyBaSrCu3O7−δ
Physics Letters A, 2001
Ultrasonic longitudinal and shear wave velocities were measured for superconducting and non-superconducting DyBaSr Cu 3 O 7−δ (Dy-1113) at 10 MHz between 80 and 270 K. The superconducting sample exhibits a step-like elastic anomaly between 190 and 230 K. No elastic anomaly was observed in the non-superconducting Dy-1113. The anomaly observed in the superconducting sample is attributed to structural phase transition caused by oxygen orderings.
Zeitschrift f�r Physik B Condensed Matter, 1990
The attenuation and the velocity of ultrasonic waves in single crystalline high-T~ YBa2Cu3OT-x have been measured in the temperature range from 3 to 280 K for the C~1-, C33-, C44-and C66-mode. At the superconducting transition a pronounced peak in the absorption is observed for the longitudinal C 11-mode. The longitudinal C~ 1-and C33-modes and the transverse C44-mode exhibit a plateau in the temperature dependence of the velocity. The temperature dependence of the absorption of the transverse C44-mode reveals a change in the slope at T~. The data are compared with the predictions derived from a thermodynamic treatment and with the results of measurements on coarse grain and fine grain sintered and sinter-forged materials.
Journal of Materials Research, 1991
The purpose of this study was to (1) examine the spatial (within-sample) uniformity of superconducting behavior and microstructure in YBa2Cu307_j: specimens over the pore fraction range 0.10-0.25 and (2) determine the viability of using a room-temperature, nondestructive characterization method (ultrasonic velocity imaging) to predict spatial variability. Spatial variations in a.c. susceptibility were observed for specimens containing 0.10 pore fraction. An ultrasonic velocity image constructed from measurements at 1 mm increments across one such specimen revealed microstructural variation between edge and center locations that correlated with variations in a.c. shielding and loss behavior. Optical quantitative image analysis on sample cross sections revealed pore fraction to be the varying microstructural feature.
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.