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1
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Conductivity and Superconductivity in Granular Materials

100%
Gazda M., Kusz B., Gackowska J., Sadowski W.
Acta Physica Polonica A
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2008
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vol. 114
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issue 1
143-148
EN
Granular metals and superconductors are very interesting materials thanks to their untypical electrical properties caused by the presence of the Coulomb effects, electron and Cooper pair tunnelling and various aspects of disorder. Most typical and widely studied representatives of this group consist of low T_c superconductor granules distributed in insulating matrix (e.g. lead in germanium matrix). In comparison with them a system of granules of high-T_c superconductors embedded in an insulating matrix is more difficult to be experimentally realised. (Bi, Pb)-Sr-Ca-Cu-O materials obtained with solid state crystallisation method may be considered as an example of granular and disordered metals and superconductors. Solid state crystallisation of initially amorphous material leads to formation of 2201 and 2212 granules embedded in the insulating or semiconducting matrix. Further annealing causes increase in size and/or the number of conducting grains and decrease in the width of the insulating barriers between them. In both cases of low- and high-T_c granular materials the main parameters, which determine their properties, are the amount of metallic phases and the tunnelling conductivity between the neighbouring grains. In this work some properties of low- and high-T_c granular materials are discussed and compared.
2
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Conductivity and Superconductivity of (Bi,Pb)_4Sr_3Ca_3Cu_4O_x Glass-Ceramics

100%
Gazda M., Kusz B., Sobiechowska E.
Acta Physica Polonica A
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2007
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vol. 111
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issue 5
713-719
EN
(Bi,Pb)-Sr-Ca-Cu-O glasses, annealed in proper conditions, transform into a granular metal and superconductor. As a result of annealing oxide superconductors belonging to the bismuth family (Bi,Pb)_2Sr_2CuO_x, (Bi,Pb)_2Sr_2 CaCu_2O_x, and (Bi,Pb)_2Sr_2Ca_2Cu_3O_x crystallize. (Bi,Pb)-Sr-Ca-Cu-O glass-ceramic samples were obtained by annealing the amorphous solid at temperatures between 500°C and 870°C. Their microstructure was studied with scanning electron microscopy, atomic force microscopy, and X-ray diffraction. The temperature dependence of resistivity in annealed samples was studied in a temperature range from 3 K to 300 K. In this work we present the influence of the microstructure on the electrical properties of the granular and disordered material composed of the 2201 and 2212 grains embedded in the nonmetallic matrix.
3
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Superconducting Lead Granular Layer Prepared by Reducing in Hydrogen Lead of Germanate Glasses

100%
Gackowska J., Gazda M., Trzebiatowski K., Kusz B.
Acta Physica Polonica A
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2006
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vol. 109
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issue 4-5
591-596
EN
The thin layer of Pb granules on the surface of the lead-germanate glass was prepared by thermal annealing in hydrogen. The structure and superconducting properties of lead layer depend on temperature and time of reduction. The influence of time and temperature of reduction on the properties of the reduced layer thickness has been studied.
4
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Chemical Interaction between Perovskite La_{0.6}Sr_{0.4}FeO_3 and Super-Ionic Zr_{0.84}Y_{0.16}O_x

88%
Gazda M., Kusz B., Płończak P., Molin S., Jasinski P.
Acta Physica Polonica A
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2008
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vol. 114
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issue 1
135-141
EN
Perovskites are materials of very versatile properties. They may be used in various ways and structures. In this work the results of investigation of the Zr_{0.84}Y_{0.16}O_x electrolyte on La_{0.6}Sr_{0.4}FeO_3 perovskite support are presented. The perovskite support was fabricated by iso-axially die-pressing of La_{0.6}Sr_{0.4}FeO_3 powders and sintering at 1150°C. The Zr_{0.84}Y_{0.16}O_x layer was deposited on La_{0.6}Sr_{0.4}FeO_3 by a combination of colloidal suspension and polymer precursor methods. In this way the dense electrolyte layer was prepared at as low temperature as 400°C. This method may be also useful for high-T_c superconductor layers deposition. The chemical interaction between the electrolyte layer and perovskite support was investigated by X-ray diffraction. It was shown that no reaction occurs between cathode and electrolyte until 900°C. Above 1200°C, parameters of the La_{0.6}Sr_{0.4}FeO_3 unit cell increase. It suggests that the reaction between Zr_{0.84}Y_{0.16}O_x and La_{0.6}Sr_{0.4}FeO_3 is accompanied by substitutional changes in the La_{0.6}Sr_{0.4}FeO_3.
5
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Superconducting Transition in Granular Bi-Sr-Ca-Cu-O Superconductors

76%
Gazda M., Kusz B., Sadowski W., Stizza S., Natali R., Di Stasio V.
Acta Physica Polonica A
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2006
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vol. 109
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issue 4-5
485-491
EN
In this work we study the superconducting transition in the samples containing relatively small granules of high-T_c Bi-Sr-Ca-Cu-O superconductors. The samples were obtained by the glass-ceramic technology. Two-stage character of the superconducting transition was studied. Pairing transition temperature depends on the magnetic field. Coherence transition is very sensitive to the current flowing through the sample, magnetic field and the phase composition and microstructure of the sample. The analysis of superconducting transition by means of the logarithmic derivative of the fluctuation conductivity shows the mesoscopic granularity of the samples.
6
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Conductivity and Superconductivity of (Bi,Pb)_4Sr_3Ca_3Cu_4O_x Glass-Ceramics

76%
Gazda M., Kusz B., Stizza S., Chudinov S., Natali R., Piętosa J., Bienias A.
Acta Physica Polonica A
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2004
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vol. 106
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issue 5
617-625
EN
In the (Bi,Pb)-Sr-Ca-Cu-O system, materials of various electrical and superconducting properties may be produced by a glass-ceramic method. Phase composition, structure, microstructure and also electrical properties of the material change as a result of heat treatment. Depending on the heat treatment conditions, either a superconductor with the critical temperature between 8 and 105 K or material without a superconducting transition may be obtained. The properties of the material change so much because during annealing three oxide superconductors belonging to the bismuth family are formed. (Bi_{0.8}Pb_{0.2})_4Sr_3Ca_3Cu_4O_x glass was prepared by a standard technique of quenching homogenized and melted substrates. The glass-ceramic samples were obtained by annealing of the glass beneath melting temperature. Structure and microstructure of glass-ceramic samples were studied with scanning electron microscopy and X-ray diffraction method. Superconducting properties were studied by means of electrical conductivity and magnetization measurements. In this paper we present the influence of the phase composition, structure and microstructure on the electrical conductivity in the normal state and the superconducting properties of (Bi,Pb)_4Sr_3Ca_3Cu_4O_x glass-ceramics.
7
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Surfaces of Electron-Emitting Glasses Studied by a Slow Positron Beam

64%
Pliszka D., Gazda M., Kusz B., Trzebiatowski K., Karwasz G., Deng W., Brusa R., Zecca A.
Acta Physica Polonica A
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2001
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vol. 99
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issue 3-4
465-472
EN
Semi-conducting glasses used for electron multipliers and microchannel plate devices are obtained by surface modification of Pb or Bi-reach silicon-based glasses. The reduced layer extends down to 200-500 nm, much more than the effective depth of the electron-emitting layer. By the use of slow-positron beam we monitor the structural changes undergoing in near-to-surface layers after isothermal annealing. The measurements suggest a possible correlation between secondary-electron emission coefficient and the Doppler-broadening S-parameter. On these samples there were also performed atomic force microscopy, secondary electron emission, differential scanning calorimetry, and electric conductivity measurements.
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