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1
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XPS Study of Superconducting LiTi_2O_4 and LiTi_{2-x}Cu_{x}O_4 Sol-Gel Derived Powders and Thin Films

100%
Łapinski M., Kościelska B., Winiarski A., Sadowski W.
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vol. 126
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issue 4a
A-107-A-110
EN
In this work X-ray photoelectron studies of lithium titanate and copper doped lithium titanate are presented. Both, powder and thin films samples were prepared by sol-gel method. After preparation, the samples were heated in argon atmosphere at various temperatures in a range from 500 °C to 600 °C for 20 h. The crystalline structure of the samples was investigated by X-ray diffraction, while the oxidation states of the elements were examined by X-ray photoelectron spectroscopy method. X-ray diffraction measurements confirmed spinel phase of all manufactured samples. However it is well known that electrical and superconducting properties of lithium titanate are strongly correlated not only with structure, but also with oxidation state of Ti ions. X-ray photoelectron spectroscopy investigations revealed mixture of Ti^{3+} and Ti^{4+} ions, although the Ti^{3+}/Ti^{4+} ratio is much smaller than 1/2 needed for superconductivity. In this work dependence between calcination temperature as well as amount of Cu dopant and Ti^{3+}/Ti^{4+} proportion are reported.
2
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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.
3
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STM/AFM Images and Tunneling Spectra of Nd_{2-x}Ce_{x}CuO_{4-y} Single Crystals

100%
Susła B., Sadowski W., Klimczuk T., Czajka R.
Acta Physica Polonica A
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1997
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vol. 92
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issue 1
209-214
EN
The results of the scanning tunneling microscopy and spectroscopy as well as atomic force microscopy measurements on the Nd_{2-x}Ce_{x}CuO_{4-y} single crystals in ambient conditions are reported. Using the scanning tunneling microscopy we were able to modify the Nd_{2-x}Ce_{x}CuO_{4-y} ab-plane in air under the conditions of sample bias voltage V_{t}=500 mV and set current I_{s}=0.3 nA. It is possible to prepare atomically flat and clean surfaces as well as to create new structures in a nanometer scale in these electron-doped materials. The similar processes were not observed during atomic force microscopy imaging.
4
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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.
5
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Superconducting Properties of VN-SiO_{2} Sol-Gel Derived Thin Films

76%
Kościelska B., Yuzephovich O., Bengus S., Winiarski A., Sadowski W., Łapiński M.
Acta Physica Polonica A
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2012
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vol. 121
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issue 4
832-835
EN
In this work studies of structure and superconducting properties of VN-SiO_{2} films are reported. The films were obtained through thermal nitridation (ammonolysis) of sol-gel derived V_{2}O_{3}-SiO_{2} coatings (in a proper V_{2}O_{3}/SiO_{2} ratio) at 1200°C. This process leads to the formation of disordered structure with VN metallic grains dispersed in the insulating SiO_{2} matrix. The structural transformations occurring in the films as a result of ammonolysis were studied using X-ray photoelectron spectroscopy (XPS). The critical superconducting parameters are obtained. The magnetoresistance at high magnetic fields has been investigated.
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