In this paper the main directions, methods and results of the investigation of high-T(c) superconductors in Hungary are briefly summarized. The fundamental idea of this research is to study the effect of starting conditions on the microstructure of samples and the influence of the latter one on their superconducting parameters. The investigation concerning technical development is also mentioned

Kirschner, I.

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PREPARATION, STRUCTURE AND SUPERCONDUCTIVITY
OF HIGH-Tc COMPOUNDS
(Researchof high temperaturesuperconductorsin Hungary)
I. Kirschner
Departmentfor LowTemperaturePhysics,E0tv0sUniversity,Budapest,Hungary
Abstract
In this paper the main directions, methods and results of the investigationof high-Tc
superconductorsin Hungaryarebrieflysummarized.Thefundamentalideaof this researchis to study
the effectof startingconditionson the microstructureof samplesand the influenceof the latter one
on their superconductingparameters. The investigationconcerningtechnical developmentis also
mentioned.
Introduction
At the beginning of this century the fundamental gravitation experiments of Lorfind
F_.6tv6sand his collaborators made the Hungarian physics to be well-known. Numerous
famous results are connected to his name, namely the E6tv6s-pendulum (which has an
importance in the research of raw materials too), Eftv6s-effect and E6tv6s-law, etc.
Before the 2nd World War the physical investigation was concentrated in the
universities and some big companies, dealing mainly with the applied research referring to
the actual needs of the industry. In this way important results have been achieved in the field
of research of metals (in particular of wolfram), noble alloys, and physical basis of the
production of incandescent lamps and high-power electrical equipments.
Many Hungarian originated physicists and chemists left their native country and
worked in the forefront of scientific research in different places of the world. Among them
Jen6 Wigner (nuclear physics), Ede Teller (nuclear physics), Mikl6s Kiirti (low temperature
physics), JAnos Kem6ny (discovery of basic language of computers), Liszl6 Tisza
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(thermodynamics), Zolt,'inBay (radar technology), Frigyes B_/my (vestibular system), T6dor
K_m/m (mechanics, who was the founder of Jet Propulsion Laboratory), D6nes G_ibor
(holography), Le6 Szil_d (nuclear physics), Gy6rgy B6k6sy (research of hearing), J_os
Neumann (mathematics), J_inosPol_inyi (dynamics of chemical process), Korn61 IAnczos
(mathematical physics), Gy6rgy Hevesy (nuclear chemistry, isotope-traces), Albert
Szent-Gy6rgyi (biochemistry) and B_ilintTelegdi (nuclear physics) are the most known. The
excellent scientific results of Wigner, G_ibor,Szent-Gy6rgyi, Hevesy, B6k6sy, B_y and
Pol_inyiwere acknowledged by Nobel-prize.
During the years of fifties a new research and development system was established,
having four sections, namely university departments, institutes of the academy of sciences,
industrial research institutes and local research and development centers of different
companies.
The physical research broadened significantly and the directions covered almost all
of the main fields of physics, e.g. quantum-mechanics, solid state physics, thermodynamics,
nuclear physics, optics, astrophysics, elementary particles, statistical physics, laser physics,
relativity theory, etc.
Some groups were successful in different areas of physical research, namely in the
investigation of cosmic rays, molecular spectroscopy, crystal growth, elementary particles,
low energy nuclear physics, evolution of the world, magnetism, neutron physics, quantum
chemistry, etc. having internationally respected results.
Activity and co-operation in high-Tosuperconductivity
The solid state physics and materials science have a rather old tradition in Hungary,
and numerous Hungarian research institutions (universities, academic institutes and industrial
research centers) act in different fields of condensed matter physics. During this research,
remarkable results obtained concerning metals, alloys, semiconductors, surfaces and technical
application of the results of the fundamental study. This activity provided the basis of the
research of low temperature phenomena, first of all superconductivity.
The main themes of our superconductivity research were the investigation of the
magnetic properties of conventional superconductors, namely In-Bi, In-T1, In-Pb, Sn-Bi, and
Sn-Sb alloys, the study of compounds and alloys having an importance from the point of
view of application, building magnets and small-scale cable sections, the investigation of the
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pinning properties and the use of the irreversible thermodynamics to describe the features of
superconductors.
In the last years, after the discovery of the high-temperature superconductivity, we
turned mostly to the investigation of the phenomena of these new superconducting
compounds.
The investigation of the high-temperature superconductivity was started in Hungary
in January 1987, based on our former experiences obtained in the course of the research of
the conventional superconductors, which began in 1963.
(1). In a small country, like Hungary, the co-operation plays a very important role
in the research work, so we have organized a very wide cooperation inside and outside
Hungary concerning this field of science. This contains the following institutions:
1. Eight laboratories of the F_,6tviSsUniversity, Budapest, (Department for Low Temperature
Physics, Department of Atomic Physics, Department for General Chemistry, Department
for Mineralogy, Laboratory for Nuclear Chemistry, Department for Petrology and
Geochemistry, Laboratory for Surface Physics and Department for Analytical Chemistry),
2. Central Research Institute of Silicate Industry,
3. Five laboratories of the Budapest Technical University (Physical Institute, Reactor,
Department of Electrical Machines, Institute of Mechanical Technology and Department
of Electronics Technology),
4. Central Research Institute for Chemistry,
5. University of Debrecen (Institute for Experimental Physics),
6. Institute for Research of Metals,
7. Central Research Institute for Physics,
8. Research Institute of Electrical Industry,
9. EPOS-PVI Electrical Inc.,
10. University of Veszpr6m (Department of Silicate Chemistry),
11. Research Institute of Technical Physics,
12. National Bureau of Standards,
13. Nuclear Research Institute of the Hungarian Academy of Sciences,
14. Ministry of Industry (Ganz Electric, Budapest Iron and Steel Company, K6b_inya
Porcelain Works, Microelectronics Ltd, Metalltech Ltd),
15. Committee of Technical Development;
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16. Finland: Wihuri Physical Laboratory (University of Turku), Microelectronics Laboratory
(University of Oulu),
17. Great Britain: Center for HTSC (Imperial College of Science and Technology, London),
Department of Physics (Glasgow University),
18. Germany: Institut fiir Festkrrperforschung (KFA, Jiilich), Lehrstuhl fiir
Tieftemperaturphysik (Humboldt University, Berlin), Forschungszentrum (Geesthacht),
Hammelwerke Sensor GmbH (Scheweningen), Physikalisches Institut (University
Erlangen-Niirnberg, Erlangen),
19. The Netherlands: Physics Department, (University of Amsterdam), Physical Institute
(University of Nijmegen),
20. Russia: Institute for Physical Problems (Moscow), Institute of High Temperature
Research (Moscow),
21. Austria: Physikalisches Institut (University of Vienna),
22. Egypt: Department for Physics (Ain Shams University, Cairo),
23. USA: Institute of Chemistry, Drexel University, Philadelphia, etc.
(2). We have developed a complex basis for preparation of samples, which included
university laboratories, academic institutes, industrial research centers and local industrial
research-development sections. The preparation work covers different profiles, containing
different methods form the solid state reaction, through explosion procedure or screen
printing, until laser ablation.
(3). In the frame of the above mentioned co-operation we have sent superconducting
samples to Italy, Germany, England, The Netherlands, Russia, Austria for investigation and
provided more, than 100 Hungarian schools with them giving the possibility for the
demonstration of the impressive HTSC effects.
(4). A specific govemmental financial support helped us to increase the level of
investigation and made possible to carry out some experiments of that kind, which could not
be done earlier due to the lack of certain up-to-date experimental equipments.
Research and results in the field of HTSC
The research performed in Hungary in this field is basically experimental, it has,
however, some theoretical and application aspects, as well.
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(1). The investigation can be treated as a complex one, because it concerns all of the
main directions in question, namely the sample preparation, physical properties and possible
technical applications.
(2). This study covers all of the known families of HTSC compounds. The properties
of La-Ba-Cu-O, Y-Ba-Cu-O, Bi(Pb)-Sr-Ca-Cu-O, T1-Ca-Ba-Cu-Oand in the latest time
Hg-Ba-Ca-Cu-O superconductors have been investigated. Different substitutions of ions and
doping processes were also performed, which is demonstrated as follows: Sr--.- Ba, Eu or
other RE--*-Y, Fe or Sn_Cu, F--*-02 and addition of Ag or LiF, in order to change the
physical or mechanical parameters of the basic superconducting compounds.
(3). The bulk samples, thick films and thin layers are equally in our interest from the
point of view of investigations.
(4). High-To superconductors, suitable to different specific purposes, (e.g. magnetic
screening) were elaborated, as elastic foils, rods and filaments, using organic and inorganic
filling materials.
(5). Certain improvements of the experimental technique were also performed
concerning the measurement of thermoelectromotive force, critical currents, a.c. resistivity
and susceptibility.
(6). During the different directions of investigation we used a rather wide spectrum
of the research methods, namely:
1. SEM, 2. X-ray, 3. TEM (HRTEM, SAED), 4. micro-probe, 5. EDS, 6. EPMA, 7. STM,
8. TG, 9. DTA, 10. resistivity measurements, 11. susceptibility, 12. SQuiD-technique,
13. ESR, 14. NMR, 15. thermodynamic cross-effect (TEMF, Hall),
16. magnetic (hysteresis), 17. dilatation, 18. SIMS, 19. detection of vortex movement,
20. ESCA, 21. M6ssbauer-spectroscopy, etc.
(7). The applied methods provide scientific information on the physical properties of
the samples, namely:
1. character of the superconducting transition (metallic, semiconducting, percolative),
2. sharpness of it, 3. effect of preparation (starting materials, their mixture, heat treatment),
4. temporal stability or instability (possible change in structural, electrical and magnetic
properties), 5. effect of external circumstances, 6. quantity of superconducting material in
specimens, 7. number, quality and share-rate of s.c. phases, 8. place and change of ions,
9. type of charge carriers, 10. degree of oxidation, 11. chemical co-ordination, 12. properties
of surfaces and grains, 13. critical parameters (To, T_ To, Hc_,Jci, _, h, K), 14. phonon-
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electron coupling, 15. gap, 16. conclusion on the fundamental superconducting mechanisms,
17. data for unit cells and their deformation, 18. anisotropy, 19. mechanical properties,
dilatation, elasticity, 20. influence of thermal cycling, 21. corrosion, degradation, etc.
(8). Due to the limited length of this paper only a few concrete results of the
Hungarian HTS-research can be enumerated to demonstrate the scope of it:
1. Just from the beginning we made the electrical and magnetic measurements together
to obtain a good chance to evaluate the Meissner's state volume of samples.
2. We have investigated in detail some important questions of high-Tocompounds, namely
the preparative chemistry consequences on Y-Ba-Cu-O superconductors, the possible role
of percolation effects in establishment of superconductivity, characteristic parameters of
T1-Ca-Ba-Cu-Ocompounds based on a very wide spectrum of preparation methods, surface
structure of different samples by STM method, effect of thermo-mechanical and water
corrosion, proximity effect, complex study of Bi-based samples, effect of neutron
irradiation, diamagnetism above To, effect of particle size on the mechanism of the
development of HTSC, improvement of the plastic properties of samples, etc.
3. Similarly to other laboratories, we also observed superconductivity at higher, than usual
To in an Y-based, temporally unstable specimen in April, 1987, but in contrast with other
results, the value of its Tc was only 105 K.
4. The elaboration of superconducting ceramic magnets with a new energy feeding, small-
scale electrical rotating machines, cryogenic liquid level sensors, magnetic field detectors
and magnetically screening elastic foils, rods and thin filaments can be mentioned among
our works for the purpose of technical development.
5. Some Hungarian researchers were dealing with the study and application of Josephson's
tunnelling and with the high-To SQUID experiment having some new and valuable
information on these questions and on their application in measuring technique.
6. The employment of the M6ssbauer-spectroscopy to find out the details of structure and
some fine effects represents an important contribution to the HTSC-research in Hungary.
It was very wide, and based on replacing sites by 151Eu,_19Sn,57Feand 57Conuclides in
order to get information about site preference, structural changes, temporal instability and
change of the phonon properties.
7. Hungarian researchers have attained remarkable results in the investigation of fullerenes,
certain part of those can be superconducting. If the chains of C60 molecules contain some
alkaline metals (e.g. K, or Rb), they can develop in the form of filaments and produce
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electrically conducting polymer-crystals, which show a metallic behaviour.
This research is also accomplished in an international (American and Swiss) co-operation.
The structure of fullerenes of different kinds of conductivity are under
investigation in Hungary, using unlike methods, e.g. ESR-, IR-, and
M6ssbauer-spectroscopy. These investigations include alkaline fullerenes, fullerene
polymers and ligandum-containing fullerenes as well.
8. Optically induced changes of the magnetic properties, created by laser beam in
La-Ba-Cu-O superconductors have been observed. According to our investigation, the
light-induced change of the magnetic moment strongly depends on the temperature at low
temperatures. The results obtained in the magnetic field of 1-26 Oe suggest, that the
observed effects have contributions from the weakening Josephson's junctions under
illumination and from the additional part of the optically induced flux creep, which
depends on the applied magnetic field.
9. In order to examine the fine details of superconducting-normal or normal-superconducting
transition, a new, so-called thermometric mapping method was elaborated. By the essence
of this method, the samples are submitted to a large and variable temperature gradient,
which broadens significantly the transition to reveal its gradual nature. This procedure is
in a strong contrast with the conventional electrical and magnetic measuring practice of
superconductivity, where a homogeneous temperature distribution is used generally to
avoid the uncertainty of results. The method is sensitive enough to detect not only the fine
structure of the transition, or to select the unlike properties of different specimens, but to
trace the change of the features of a given sample too.
(9). Comparing to the international research of HTSCs, we investigated firstly some
important questions of this field, which were as follows:
1. building high-Tosuperconducting ceramic magnets, 2. synthesis and application of a new
precursor Ba2Cu3Os, 3. investigation of the corrosion effects, 4. elaboration of the
thermometric mapping method, 5. Mrssbauer-study of Tl-based superconductors,
6. cryogenic liquid level sensor based on TEMF, 7. a new method for preparing Y-based
superconductors, 8. observation of the fine structure of S-N or N-S transition, and
9. elaboration of a microwave magnetic field detector. At the same time Hungarians were
among the first groups to measure TEMF, to develop ceramic HTSCs workable by machine-
tool, to elaborate elastic foils, rods and filaments and to build small electrical rotating HTSC
machines.
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Publications
In the course of investigation of high-To superconductors we have reached
internationally respected results, published over 150 scientific papers, elaborated some
patents and introduced the fundamental phenomena of high-temperature superconductivity
into the education of universities and secondary schools. Among them, we have the exact
number of the publications of one of the Hungarian high-To laboratories. This is the
Department for Low Temperature Physics, Ertvrs University, which published 75 scientific
papers, 3 patents and 15 studies and dissertations on the methods, results and applications
between 1987 and 1993.
Conclusions
On the basis of the facts analyzed in this paper, certain conclusions can be drawn, as
follows:
1. A small country can also be effective in the field of a given branch of scientific
research, if the aim is chosen right, the powers are concentrated rationally and the co-
operations are organized operatively [1].
2. Hungarian scientists attained significant results in different areas of high-To
superconductivity and contributed successfully to the world-wide research, because they
utilized effectually the internal and the possibilities of international co-operations [2].
References
1. I. Kirschner, J. B_kuti, M. Gilland K. Torkos, Phys. Rev. B36. 2313. 1987.
2. I. Kirschner,S. Lepp_ivuori,R. Laiho, A.D. Caplin,T. K_mAn, E. Lfthderanta,
G. Zsolt, A. Uusim_ki,J. Laverty,T. Porjesz, I. Hal_iszand Gy. Kov_ics,
Zeitschr. Phys. B78. 381. 1990.
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Preparation, structure and superconductivity of high T(c) compounds: Research of high temperature superconductors in Hungary

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