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1
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Internal Barrier Layer Capacitance Effects in Neodymium Copper Tantalate Ceramics

100%
Szwagierczak D.
Acta Physica Polonica A
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2012
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vol. 121
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issue 1
205-207
EN
A new perovskite material Nd_{2/3}CuTa_4O_{12} was applied as a naturally formed internal barrier layer capacitor. The powder prepared by solid state synthesis and ball milling was pressed into pellets and sintered at 1180-1220°C. Dielectric properties of ceramic samples were characterized by impedance spectroscopic studies carried out in the temperature range from - 55 to 700C at frequencies 10 Hz ÷ 2 MHz. Two types of the dielectric response were revealed - a high frequency response attributed to grains which occurred at low temperatures, and a low frequency one related to grain boundaries which dominated at higher temperatures. Resistances and capacitances of grains were found to be two orders lower than those of grain boundaries. Two plateaus were observed in the dielectric permittivity versus frequency plots - a low frequency step corresponding to a high value of 10^4 and a high frequency step at a level of 40. Scanning electron microscopy observations and energy dispersive spectroscopy analysis confirmed that Nd_{2/3}CuTa_4O_{12} ceramics were composed of semiconducting grains and insulating oxygen-enriched grain boundaries. The formation of such an electrically heterogeneous system during the one step fabrication process in air leads to spontaneous internal barrier layer capacitance effects responsible for a high and relatively stable dielectric permittivity of the developed material.
2
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Application of High Permittivity Bismuth Copper Titanate in Multilayer Capacitors

63%
Szwagierczak D., Kulawik J.
Acta Physica Polonica A
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2012
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vol. 121
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issue 1
119-121
EN
A nonferroelectric high permittivity compound with the perovskite structure, Bi_{2/3}Cu_3Ti_4O_{12}, was synthesized at 900°C. The ceramic powder and appropriate organic additives were used for preparation of a slurry for tape casting. The obtained green tapes were smooth, flexible, and with a uniform thickness of 25 μm after drying at 50°C. Ag electrodes were screen printed on green rectangular sheets cut by a laser. Subsequent operations were screen printing of Ag internal electrodes, stacking of green sheets, isostatic lamination, cutting, deposition of external terminations and co-firing of dielectric and conductive layers at 850°C. Scanning electron microscopy observations showed well sintered, dense, fine-grained microstructure of ceramic layers and good cooperation with the electrodes made of commercial Ag paste. Capacitance and dissipation factor of multilayer capacitors were examined in the temperature range from - 55 to 330C at frequencies 10 Hz-2 MHz. The fabricated multilayer capacitors exhibit high capacitance and relatively low temperature coefficient of capacitance in the temperature range from - 55 to 110°C. The obtained lead-free high permittivity nonferroelectric material Bi_{2/3}Cu_3Ti_4O_{12} is a spontaneously formed internal barrier capacitor. This material seems to be a promising alternative for conventional lead-based relaxor dielectrics in multilayer ceramic capacitors.
3
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Multiferroic Cobalt Ferrite-Lead Iron Tungstate Composites

51%
Kulawik J., Szwagierczak D., Guzdek P.
Acta Physica Polonica A
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2012
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vol. 121
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issue 1
122-124
EN
The paper presents dielectric, magnetic and magnetoelectric properties of multiferroic bulk composites based on CoFe_2O_4 ferrite and Pb(Fe_{2/3}W_{1/3})O_3 relaxor. X-ray diffraction analysis and scanning electron microscopy observations of ceramic samples revealed two-phase composition and fine grained microstructure with uniformly distributed ferromagnetic and ferroelectric phases. Dielectric permittivity measured in a temperature range 218-773 K at frequencies of 10 Hz-2 MHz exhibits high and broad maxima attributed to dielectric relaxation. The hysteresis determined in a temperature range 4-393 K for magnetic field changing from - 80 kOe to 80 kOe is typical of hard magnetic materials. Saturation magnetizations and coercivities were found to decrease with increasing temperature. The courses of zero field cooled and field cooled magnetization versus temperature curves measured in the temperature range 4-393 K imply spin glass behavior of the ferrite and antiferromagnetic transition of the relaxor at low temperatures. The ferrite-relaxor composite shows high magnetoelectric voltage coefficient which distinctly increases with increasing frequency of ac magnetic field and is slightly higher for higher ac and dc magnetic fields.
4
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Investigations of properties of ceramic materials with perovskite structure in chosen electronic applications

51%
Kulawik J., Szwagierczak D., Gröger B.
Bulletin of the Polish Academy of Sciences: Technical Sciences
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2007
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vol. 55
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issue 3
5
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Multilayer Perovskite-Based Thermistors Fabricated by LTCC Technology

45%
Kulawik J., Szwagierczak D., Witek K., Skwarek A., Gröger B.
Acta Physica Polonica A
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2013
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vol. 123
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issue 2
436-438
EN
In this work, single-phase La_{0.7}Sr_{0.3}Zr_{0.5}Co^{2+}_{0.2}Co^{3+}_{0.3}O_3 and La_{0.8}Sr_{0.2}Ti_{0.5}Co^{2+}_{0.3}Co^{3+}_{0.2}O_3 ceramics with the stable perovskite structure were utilized for fabrication of multilayer negative temperature coefficient thermistors. The number and thicknesses of ceramic layers were adjusted to attain suitable resistances in a desired temperature range. Scanning electron microscopy studies revealed a dense, fine-grained microstructure of ceramic layers, lack of delaminations and cracks at ceramic layer-conductive layer boundaries and a good cooperation with conductive layers. The temperature coefficients of resistance of the fabricated multilayer thermistors were changing from - 13 to - 1%/K in the temperature range from - 55 to 400C.
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