Post-annealed thin films comprised of mixed YBa2Cu3O7-x (123) and Y2Ba4Cu8O16 (248) phases with both faulted and unfaulted microstructures have been characterized by planar and cross-section transmission electron microscopy. The influence of 248-type faults on the 123 structure, possible mechanisms for the higher Tc's of faulted films, and observations of a fourfold ordered structure are discussed.

Mixed-phase superconducting YBaCuO is characterized by means of high-resolution transmission electron microscopy. This technique reveals that such material contains numerous crystallographic defects of various types. Several of these are described in detail, and their origins discussed.

We have conducted structural and magnetic investigations on thermomechanically-detwinned YBa2Cu3O6+x single crystals. Single crystal x-ray diffraction studies on a fully untwinned crystal with a superconducting onset temperature of 54 K have revealed that oxygen atoms in the basal plane are offset from the crystallographic mirror plane in the a direction, leading to “zig-zag” Cu-O chains. Magnetic measurements on untwinned and twinned crystals at 77 K indicate low levels of flux pinning in both crystals, with a slightly larger amount of pinning in the twinned crystal.

We find by transmission electron diffraction (TED) that the orthorhombic splitting of the upper surface layers (< 1 μm) of single crystal Ba2YCu3O7-δ(YBCO) is reduced, differing by 10 to 30 percent from the bulk value. We also find by transmission electron microscopy (TEM) that in general the surfaces are of inferior quality, and thus, not representative of the bulk. These results have important consequences for those experiments that probe only the upper surface layers. By etching with either Br/ethanol or HClO4/NaClO4 the poor quality surfaces can be removed.

The domain structure of oxide superconductors arises as a result of twinning associated with the tetragonal-orthorhombic transition inside a restricted volume (a grain in a polycrystal, an epitaxial layer, or a part of an initial single crystal). A thermodynamic theory of the size and arrangement of the domains has been developed. There are two types of interfaces in equilibrium domain structures: coherent twin boundaries and boundaries between polytwin layers with microstresses. Elastic vortex-interface interactions have been estimated.

The formation of twins in the YBa2Cu3O7‐x system has been studied theoretically on the basis of transmission electron microscopy observations. The shape of the lips of the twinned domains is determined from two elastic strains, one associated with the twin boundary and the other with the lattice distortion at the lip region. The tangent of the angle at the tip which was calculated from the model agrees with experimental observations sufficiently well. The growth mechanism of the twinned domains is analyzed with an energy minimization approach. The similarities of transformation characteristics in this system to those of other systems are briefly discussed.

In this short report, we describe some of the structural defects present in laser deposited Y‐Ba‐Cu‐O thin films. Many of the defects observed are polytypoidic variants, related to the layered structure of these cuprates. One possible model by which flux pinning can be achieved is presented.

The surface morphology and internal structure of a superconducting screen printed thick film of YBCO has been examined by means of optical and scanning electron microscopy. The highly textured track was sintered at a temperature above the peritectic temperature of the 123 phase, and the resulting characteristic spherulitic morphology has been found to be associated with underlying elongated strands of CuO. The composition of the inter‐diffusion layer formed at the film/substrate boundary is consistent with a Ba(Zr,Cu)O3 solid solution with small concentrations of yttrium.

Geometrical modelling of grain boundaries in 123‐YBaCuO and 2223‐TlBaCaCuO systems is carried out for several misorientat‐ions. The a‐b and the a‐c type coincidence boundaries are analyzed to determine the fraction of Cu‐O planes that are continuous and the excess charge present at the boundary voids. The interg‐rain critical current density is determined as a function of the misorientation and the width of the boundary. The tunneling of superconductor pairs through the regions of distortions, giving rise to depression of the order parameter at the boundaries,is used to determine the critical current density in the weak coupling limit.

The results of transmission electron microscopy studies on YBa2Cu3O7‐x subjected to high temperature extrusion are presented. Particular emphasis is put on high temperature accommodation processes of lattice dislocations into sub‐grain boundaries. It is suggested from the electron microscopy observations that stress induced climb mechanisms for dislocations are operative. Also presented is evidence of localized lattice distortions near twin boundaries due to isothermal high temperature deformation. Preliminary results on the structure of grain boundary facets and steps is described. The implications of these results for texture development in bulk ceramic superconductors is also discussed.

High resolution transmission electron microscopy during in‐situ quenching of YBa2Cu3Oz is used to study the kinetics of microdomain formation during oxygen loss in this system. Image simulations based on atomic models of oxygen‐vacancy order in the basal plane of this material generated by Monte Carlo calculations are used to interpret high resolution micrographs of the structures obtained by quenching. The observed domain structures agree well with those obtained from the simualtions.

Microstructural changes in a Ba2YCu3O7 pellet were continuously observed during electron irradiation in a transmission electron microscope operating at 200 kV. Twin lamellae of 2~10 nm in thickness with 1~50 nm spacings were seen parallel to the lattice image of (001) plane with 1.17 nm in lattice spacing. The tip of the twin was lenticular and the (001) lattice fringes were distorted around the tip. Upon intense electron beam illumination, the lamellae faded at the tip and the thickness gradually decreased which increased the spacing in the high density region. Defect clusters of about 10 nm in size were produced in the very early stage of electron illumination.

(Bi, Pb)-Sr-Ca-Cu-O ‘2223’ wires with varying Bi/Pb ratios and sinter times have been investigated by parallel physical measurements and analytical electron microscopy. The numbers of phases present, their relative amounts, compositions and structures are reported and correlated with the superconducting properties. In particular, the recently reported long period (010) modulation (2b*/q*=7.7) is found to be connected with the “2223” high Tc phase.

The fundamental processes governing the appearance of dissipation due to flux motion in superconductors are reviewed. The dominant thermally‐activated resistive processes are discussed, and evidence for a sharp melting transition of the flux lattice is assessed.

Recent measurements of the dissipation in cuprate superconductors in a magnetic field have been interpreted as providing evidence for the presence of new phases in type II superconductors: flux liquids or flux glasses. We suggest that a more conventional interpretation in terms of the electrodynamics of vortices can adequately account for all the observations. Based on this model, we propose a magnetic phase diagram.

Kosterlitz‐Thouless properties of laser deposited high Tc superconducting thin films of YBa2Cu3O7‐x were examined. The exponent of the power law dependence of V on I showed a “universal jump” at Tc. ID like conductivity fluctuation was also found at temperatures slightly above the mean‐field transition temperature Tco, which may be the result of imperfections of the sample.

Measurements of the critical current density Jc for ultrathin YBa2Cu307‐X (YBCO) films are presented.A high Jc value at 77K in zero field of 2xl06A/cm2 was obtained in a 30nm thick film and even a 5nm thick film could carry a supercurrent of 3.5x105 A/cm2 at 4.2K in zero field. A very weak field‐dependence of Jc was observed when the field was in the (a,b) plane showing greatly depressed dissipation.

Experimental studies of the resistive state of high temperature superconductors in the mixed state were carried out on thin film samples of YBa2Cu3O7‐y and Bi2Sr2CaCu2Os+y. Precise angular dependence measurements on Yba2Cu3O7‐y epitaxial film have revealed not only the critical field anisotropy with respect to the a, b, and c‐axes but also a feature associated with twin boundaries. Dependence on the angle between the transport current and the magnetic field is investigated and discussed in terms of flux dynamics in highly anisotropic layered superconductors. Peculiar behavior of the Hall effect in the resistive state is reported.