P. van der Linden

A new procedure for the isolation of large YBCO superconducting single crystals

Abstract A new procedure, the liquid flow method, is reported for the separation of large YBCO superconducting single crystals from the flux. We used a shallow alumina boat with a slope of 20°–30°. The slope of the boat could be changed without disturbing the temperature. Single crystals up to 5–10 mm have been obtained; the superconducting transition occurs at about 90 K. The liquid flow method is one of the best techniques for a smooth separation of the flux and the detachment of the as-grown crystals from the crucible.

Double crucible method for the growth of large superconducting YBCO single crystals

In this paper we report an effective procedure for the growth of large superconducting YBCO single crystals by using a double crucible method which facilitates detachment of the as-grown crystals from flux. As-grown crystals with dimensions up to 5 × 5 mm2 have been obtained. The Superconducting transition occurs at about 90 K. The growth principle is based on the melt growth and phase separation method. We find that by using BaO2 instead of BaCO3 as raw material, the quality of as-grown crystals was much better and the superconducting transition temperature was a few degrees higher than in case of using BaCO3.

Epitaxial high Tc cuprate superlattices: A study of the thermal flux motion

Abstract Epitaxial c-axis YBa 2 Cu 3 O 7 /PrBa 2 Cu 3 O 7 (YBCO/PrBCO) superlattices grown by single target dc planar magnetron sputtering are used as a model system to investigate the nature of flux motion in high T c superconductors (HTS). When a magnetic field H is applied parallel to the c-axis we find that, for sufficiently thick PrBCO layers, the activation energy for flux motion U is proportional to the YBCO thickness. This allows us to extract a lower limit, about 500A, for the correlation lenght along the vortices in pure YBCO. We find also for thin YBCO layers that U∼lnH which could be the signature that the dissipation process is related to the creation in the 2-D vortex lattice of dislocations pairs. When the field is applied in the a-b plane we find for thin YBCO layers separated by thick enough PrBCO layers that the resistive transition becomes field independent. Measurements on a 24A/96A YBCO/PrBCO multilayer up to 20T do not show any broadening of the resistive transition. We also find that the activation energy for flux motion decreases with decreasing the YBCO thickness and is insensitive to magnetic field below the H c1 of the individual YBCO layers.

Excess electrical conductivity in Bi-Sr-Ca-Cu-O compounds

We report on measurements of the resistivity of high quality (Bi 1− x Pb x ) 2 Sr 2 Ca 2 Cu 3 O 10+ y ceramics and single crystals of the (Bi 1− x Pb x ) 2 Sr 2 CaCu 2 O 8+ y phase. The resistivity is perfectly described by the theoretical expression for excess conductivity in the case of a two component order parameter fluctuating in two dimensions. The resistance data can be exactly fitted by one set of parameters starting from the critical temperature up to about 200 K.

Anisotropic magnetotransport in high temperature superconductor multilayers

The high temperature superconducting cuprates are layered materials in which the CuO2 layers are found to play an important role for the superconducting properties. When produced in thin film form, these materials can be grown in a layer by layer sequence and this has allowed us to make superlattices of various combinations of these compounds. In particular, in the YBa2Cu3O7/PrBa2Cu3O7 system it is possible to produce superlattices where the individual layers are as thin as one c-axis unit cell. This allows us to modify the anisotropy of these materials in a controlled manner. In this contribution we present a study of the resistive transition in a magnetic field perpendicular or parallel to the layers, and how the results can be used to gain insight into the role of the anisotropy for the dissipative behaviour of these high temperature superconductors.

Automated system for resistance and critical current measurements

An apparatus is described for measuring the temperature and magnetic field dependencies of the resistance and critical current of high‐temperature superconductors. The automated setup together with a set of inserts forms a universal system allowing for fast sample selection as well as for accurate complementary measurements at temperatures from 4.2 to 300 K and in high magnetic fields up to 30 T. Design details and low resistance measuring algorithm are presented and system peformance is discussed.

Seeded growth, morphology and surface topology of superconducting Bi-Sr-Ca-Cu-O single crystals

In this paper we describe two seeding growth techniques for the growth of large superconducting Bi-Sr-Ca-Cu-0 single crystals. YAP (yttrium alumina perovskite, YA103), and BGO (bismuth germanate, Bi4Ge301z) pseudo-seeds were used for top-seeding growth; the liquid phase separation (double crucible) method was improved so that large single crystals could be grown more or less free from the flux. The morphology and surface topology of as-grown crystals was investigated using differential interference contrast microscopy (DICM), scanning electron microscopy (SEM) and scanning tunneling microscopy (STM).

New dielectric material for low temperature thermometry in high magnetic fields

Dielectric experiments on the incommensurate solid solution (Pb0.45Sn0.55)2P2Se6 for T=1.2–200 K reveal a strong temperature dependence of the real part of the dielectric constant for T<45 K. The relative dielectric sensitivity d ln(e’)/dT≊2–8 K−1 is found to be 2–3 times higher in comparison to widely used glass‐ceramic temperature sensors. Moreover, the dielectric constant has a very good time stability and is insensitive to magnetic fields up to 20 T (dT/dB<10−4 K/T). These characteristics make this material a very promising candidate for applications in capacitive temperature sensors for low temperature thermometry in high magnetic fields.

Crystal growth and surface morphology of Pb, Bi, Sr, Ca, Cu, O, high Tc superconductors

Two types of Pb, Bi, Sr, Ca, Cu, O superconducting single crystals: plate with a flat surface and bulk mica-like were successfully grown by a slow cooling method. As-grown crystal dimensions up to 1 cm2 have been obtained. Magnetization and resistivity measurements indicate that the as-grown single crystals have a superconducting transition temperature at 85–90 K. Surface morphology observations by means of differential interference contrast microscope (DICM) and scanning tunneling microscope (STM) are reported.

Growth and superconducting properties of (Bi1 − xPbx)2Sr2CaCu2O8 single crystals

Superconducting single crystals of the compound (Bi1 − xPbx)2Sr2CaCu2O8 with a critical temperature above 80 K have been synthesized using the method reported by Wang Hong et al. (1). The X-ray diffraction data do not confirm the existence of a new superconducting phase in spite of the similarity of the powder X-ray diffraction patterns to those of Ref. 1. The estimated lattice constants, a = 5.4 A, b = 5.4 A, c = 30.8 A, and the composition are characteristic of the 80-K phase of the Bi compound family. The electrical and magnetic measurements indicate a high crystal anisotropy.