G.M. Lin

An investigation of the migration of oxygen deficiencies in the superconductor YBa2Cu3O7δ

The temperature and oscillation frequency dependences of internal friction and shear modulus of superconducting YBa2Cu3O7- delta specimens are measured using a multifunction internal-friction torsion pendulum to study the degree of ordering and the migration of oxygen deficiency sites in the superconductor YBa2Cu3O7- delta . It is found that relaxation is most likely to occur in units where one oxygen site is surrounded by four barium ions rather than along the O-Cu-O chain. This indicates that an internal-friction study provides a powerful way of investigating the relaxation process of oxygen atoms as well as the degree of ordering of oxygen deficiencies in relation to superconductivity features.

Anelastic relaxation of oxygen vacancies and high-Tc superconductivity of YBa2Cu3O7-δ

It is suggested that the variation of the internal friction (IF) characteristics of a single-phase YBCO specimen resulting from an increase of oxygen deficiency δ is associated either with an order diffusion process between layers, or with an order/disorder diffusion process in the Cu(2) plane. The experimental results are explained in the light of these oxygen-vacancy migration processes. The essential connections between high-Tc superconductivity, electric behaviour and oxygen-vacancy ordering are discussed.

A study of internal friction phenomena at 300–420K in the Bi-based high Tc superconductor system

Abstract The self-induced ordering process and the superconductivity property of BiSrCaCu 2 Ox and Pb 0.34 Bi 1.72 Sr 2 Ca 1.2 Cu 2.5 Fe 0.22 Oy have been investigated based on internal friction (IF) experiment, x-ray diffraction and thermoanalysis. It is found that the IF peak at 300–420K is associated to the superconductivity property. We discuss the physical consequences arising from migration of oxygen atoms.

Internal friction study of high Tc BSCCO ceramic superconductor within the temperature range 88–623 K

Abstract Using internal friction and shear modulus measurements, we studied certain characteristics of relaxation and phase-like transitions which could accompany conductor-superconductor transition of BiSrCaCu2Oy when samples were sintered at different temperatures and went through thermocycles.

Very low-frequency anelastic study of YBa2Cu3O7-δ in thermal cycling

Internal friction (IF) measurement techniques are used to study high-Tc superconducting cuprates. IF peaks associated with oxygen deficiency are located over a temperature range from room temperature to 623 K at frequencies from 10-2 to 5 Hz. IF characteristics, i.e. activation energies, relaxation strength and ordering critical temperature, are investigated in relation to the orthorhombic-to-tetragonal transition, superconducting properties and electrical behaviour with progressively increasing oxygen deficiency, achieved through appropriate thermal cycling. Relationships between these properties are discussed and it is suggested that a fundamental connection exists between the migration of oxygen vacancies and the onset of superconductivity.

Evolution of the orthorhombic phase and superconductivity in YBa2Cu3O7-x

Abstract The time evolution of the orthorhombic phase from starting materials of YBa 2 Cu 3 O 7-x compound in the sintering process is examined using in situ high temperature X-ray diffraction analysis. Two transition stages have been discovered: the first stage occurs in the high temperature (950°C) region, where the tetragonal perovskite like layer structure undergoes a reorganization in lattice parameter; the sesond transition takes place at about 700°C during the cooling process. This transition concern the change of oxygen content and vacancy state. The effect of first transition on the superconductivity has been studied.

Thermal cycling effects in Cu-Zn-Al shape memory alloy by positron lifetime measurements

Abstract The present paper shows that Mf and As of CuZuAl shape memory material will decrease with increasing number of thermal cycles, while Ms and Af remain constant. On the other hand, the thermal hysteresis will decrease and the shape memory strain will remain constant. The thermal cycling behaviour is closely related to the formation of vacancy clusters by vacancy agglomeration.

Evolution of the orthorhombic phase and superconductivity in YBa2Cu3O7−x

Abstract The time evolution of the orthorhombic phase from starting materials of YBa 2 Cu 3 O 7−x compound in the sintering process is examined using in situ high temperature X-ray diffraction analysis. Two transition stages have been discovered: the first stage occurs in the high temperature (950°C) region, where the tetragonal perovskite like layer structure undergoes a reorganization in lattice parameter; the second transition takes place at about 700°C during the cooling process. This transition concerns the oxygen content and vacancy states on the basal plances. The effect of first transition on the superconductivity has been studied.

A NEW METHOD FOR QUANTITATIVE STUDY OF FLUX PINNING IN TYPE II SUPERCONDUCTORS

The motion equation with an interaction force between flux and applied H is established and resolved for the moving flux in the process of magnetization of type II superconductors. The expressions of energy dissipation and the dynamic pinning force exerted on the moving flux can therefore be acquired when the low frequency internal friction, modulus and magnetization curve are measured simultaneously in the process of magnetization with a variety of applied magnetization rate H.

INTERNAL FRICTION PEAK DUE TO MOVING FLUX IN BSCCO BULK SUPERCONDUCTORS

The low-frequency internal friction in the magnetization process is measured as a function of applied field H for (Pb 0.2 Bi 0.8 )SrCaCu 2 O x at a temperature below T c . An internal friction peak is found at H 45x10 -4 T and is concluded to associate with the moving flux. A new method of investigating the dynamics and the pinning mechanism of flux in high-T c superconductor is discussed.