EFFECT OF CA-DOPING ON GRAIN BOUNDARIES AND SUPERCONDUCTING PROPERTIES OF YBA(2)CU(3)O(7-DELTA) Page: 2 of 6
This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
1
Effect of Ca-doping on grain boundaries and
superconducting properties of YBa2Cu3075
Andrey V Berenov, Roger Marriott, Steven R Foltyn, Judith L MacManus-DriscollAbstract- It is well known that the properties of grain
boundaries in YBa2CuOa7 films differ drastically from bulk
material. It has been shown both experimentally and
theoretically that the grain boundaries in YBa2Cu30728
superconductors are depleted of carriers as compared to the
bulk. This depletion leads to weak intergrain links and limits
critical currents in superconductor. Recently, the promise for
improved grain boundaries has been shown in Ca-doped
YBa2CusO7- thin films and in Ca doped YBa2Cu307.z biaxial
grain boundaries. In this study, the effect of Ca-doping of
grain boundaries in YBa2Cu307. films and bulk have been
investigated in an attempt to increase hole concentration at the
grain boundaries and to improve Jc.
Ca-gels were applied to sintered YBa2Cu3Oai pellets and
thin films. High temperature post-anneals were used to diffuse
Ca preferentially into the grain boundaries. The distribution of
Ca in the samples was studied by secondary ion mass
spectrometry (SIMS). The effect of Ca-doping on Tc and Jc
was studied by VSM. In epitaxial thin film increased Jc were
found at 40K, but not at 77K.
Index Terms--Critical currents, Grain boundaries, SIMS.
I. INTRODUCTION
G RAIN boundaries in YBa2Cu307s plays an important role
in modifying superconducting properties. It has been
suggested that a charge transport across a grain boundary
occurs by the tunneling through an insulating layer of
thickness 2Id+8, where Id and S are widths of one charge
depletion layer and a grain boundary, respectively [1].
The width of depletion layer, is given as [1]
_ 2A0& Vbi
d n
where Pee, is dielectric constant of material, Vbi is built-in
potential of the boundary, e is the carrier charge and n is the
carrier concentration. Hence aliovalent doping of the grain
boundary with cation like Ca would increase the number of
carriers and improve superconducting properties. Recently
Schmehl et al. [2] have demonstrated an order of magnitude
increase of inter-granular Jc's in artificial 241 [001]-tilt grain
Manuscript received September 17, 2000. This work was supported in
part by the EPSRC under Grant No. GR/L 98749.
A.V.Berenov, R. Marriott, J.L MacManus-Driscoll are with the
Department of Materials, Imperial College of Science Technology and
Medicine, Prince Consort Road, London, SW7 2BP, UK (telephone: +44 207
-594-6742, e-mail: a.berenov @ic.ac.uk).
S.R. Foltyn is with Superconductivity Technology Center, Los Alamos
National Laboratory, Los Alamos, New Mexico 87545, USAboundaries after Ca doping.
In order to preferentially dope grain boundaries, the
knowledge of Ca diffusion in the bulk as well as along the
grain boundaries is required. Several studies of the cation
diffusion in YBa2Cu3O7-4 have been published [3,4].
However no data on Ca diffusion in YBa2Cu3O,-7 was found
in the literature.
The aim of our research was to measure Ca diffusion in
YBa2Cu07.s and, based on this data, preferentially dope
grain boundaries with Ca to enhance inter-granular Jc.
Before studying specific grain boundary angles, we have
undertaken a preliminary study of epitaxial thin films and
bulk material to fin the optimum conditions for grain
boundary doping.
II. EXPERIMENTAL
A. Sample Preparation
Thin films of YBa2Cu3O7-4 were grown epitaxially on
(100) single crystal SrTiO3 by pulsed laser deposition
(PLD). A detailed description of the film deposition
conditions is given elsewhere [5]. A deposition, the Films
were cut in 5 x 2 mm pieces. In order to study Ca diffusion
in polycrystalline ceramics, several pellets were isostatically
pressed up to 300 MPa from YBa2Cu307. powder (SSC Inc.)
and sintered in air at 1000*C for 12 hrs. The density of the
obtained pellets was greater than 95%.
A dilute (0.05M) solution of Ca(N03)2 (99.99+% Aldrich
Chemical Co.) was dropped on the surface of the fitms and
pellets on a hot plate. One set of films (YE1 series) was
annealed at 870*C in air for different times in order to study
the effect of Ca-doping on the superconducting properties,
and another set of films (YE2 series) was annealed at
different temperatures, in air, in order to determine the
activation energy of Ca diffusion in YBa2Cu3O7.8. All the
films annealed at 870*C (YEl series and YE202) were later
oxygenated in flowing air at 500*C for 2 days. In order to
determine the Ca diffusion coefficient in the bulk ceramic
samples, they were annealed at 870*C in air for 2 hrs.
Several films and pellets were not doped and used as
reference samples. The preparation conditions of all samples
are given in Table I.
B. SIMS measurements
The isotope concentration profiles were measured by a
secondary ion mass-spectrometer (Atomika 6500) using a 8
kV Xe+ primary beam at normal incidence. The rastered area
Upcoming Pages
Here’s what’s next.
Search Inside
This article can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Article.
BERENOV, A. V.; MARRIOTT, R. & AL, ET. EFFECT OF CA-DOPING ON GRAIN BOUNDARIES AND SUPERCONDUCTING PROPERTIES OF YBA(2)CU(3)O(7-DELTA), article, September 1, 2000; Los Alamos, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc719586/m1/2/: accessed April 22, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.