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1

Preparation and investigations of electrical and optical properties of thin composite layers PAN/SiO2, TiO2 and Bi2O3

Matysiak W., Jarka P., Tański T.

Archives of Materials Science and Engineering

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2018

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Vol. 91, nr 1

15--22

EN

Purpose: The aim of this study was to present the influence of mass concentration of the reinforcement phase on the structure and optical properties of the obtained composite thin films with a polymer matrix reinforced by SiO2, TiO2 and Bi2O3 nanoparticles, produced by the spin-coating method. Design/methodology/approach: To produce composite materials, 10% wt. polymer solutions of polyacrylonitrile (PAN) and N, N - Dimethyloformamide (DMF) were used, containing nanoparticles with a mass concentration ratio of, sequentially: 0, 4, 8, 12%. The morphology, structure and chemical composition of the obtained thin films were determined on the basis of surface topography images, taken using atomic force microscopy (AFM) and a scanning electron microscope (SEM) with EDX and QBSD spectrometers. In order to analyse the optical properties, UV-Visible spectroscopy (UV-Vis) was used. The width of the band gap was determined on the basis of the absorption spectra of radiation (UV-Vis). Findings: The carried out morphology and surface structure research showed that with increasing mass increased porosity of the produced coating surface was observed. In addition, the greater the diameter of the applied ceramic nanoparticles, the more noticeable this effect was. The analysis of the optical properties of the obtained nanomaterials, carried out based on the registered spectra in absorption function of the wavelength, revealed a strong absorption of this type of layers under ultraviolet radiation. Research limitations/implications: The nanostructured materials as components provides nanocomposite optical properties, such as absorption and width of the energy gap. In addition, nanoparticle content causes changes of the surface morphology, which is an important parameter of thin films in potential applications. Originality/value: The properties of films depend not only on the individual components used, but also on the morphology and the interfacial characteristics.

2

Influence of Bi2O3 addition on structure and dielectric properties of Ag(Nb0.8Ta0.2)O3 ceramics

Cao L., Li L., Zhang P., Wang H.

Materials Science Poland

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2011

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Vol. 29, No. 1

1--8

EN

The structure and dielectric properties of perovskite Ag(Nb0.8Ta0.2)O3 ceramics were explored. A small amount of Bi2O3 was used to modify the dielectric properties of the ceramics. The addition of Bi2O3 led the ceramics to a high densification and optimal dielectric properties. With the addition of 4.5 wt% Bi2O3, the permittivity of Ag(Nb0.8Ta0.2)O3 ceramics increased from 470 to 733, the dielectric loss decreased from 62×10-4 to 6.7×10-4, and the temperature coefficient of capacitance, TCC, decreased from 2004 ppm/°C to -50 ppm/°C. The high permittivity obtained was due to the high densification and weak Ta-O or Nb-O bond strength in the oxygen octahedron that results from the addition of Bi2O3.

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Potentialities of modification of metal oxide varistor microstructures

Mielcarek W., Prociow K., Warycha J.

Materiały Elektroniczne

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2009

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T. 37, nr 1

86-98

EN

The electrical properties of varistors, similarly like posistors and other devices made of semiconducting ceramic, are controlled by grain boundaries. In varistor conductivity the main role play potential barriers which arise at grain boundaries during varistor sintering. The I-V behavior of varistor ceramic is such that during conduction the varistor voltage remains relatively constant while a current changes are of several orders of magnitude. Varistor is produced by sintering a mixture of ZnO with a small addition of Bi2O3 and other metal oxides. Varistor microstructure composes of ZnO grains. Each ZnO grain acts as it has a semiconducting junction at the grain boundary. The non-linear electrical behavior occurs at the boundary of each ZnO grain. The junctions between grains are separated by an intergranular phase. The best varistor performance is attained when the Bi-rich intergranular layer is of nanometer size. When the intergranular phase is in a shape of agglomerates embedding Bi2O3 crystal phases and spinel grains it forms areas excluded from conduction. The problem has been studied with emphasis on determining the relation between ZnO dopants and microstructure evolution. It was established that the vulnerability of varistor ceramic for formation of agglomerates depend on the composition of additive oxides. With SrO, MnO and PbO varistor ceramic is more susceptible for formation of agglomerates, while Co2O3, Sb2O3 and SnO2 facilitates the homogenous distribution of additives in varistor body. Elimination of an electrically inactive areas from varistor body would enable the decrease of the amount of additives (e.g. the amount of Bi2O3 would decrease from 1 mol % to 0.2 mol %) and bring about the diminishment of the cost of varistor processing along with improvement of varistor performance.

PL

Własności elektryczne warystorów, podobnie jak pozystorów i innych wyrobów z ceramiki półprzewodnikowej, są kontrolowane przez ukształtowanie granicy ziaren. Ceramika warystorowa ZnO swoje niewłaściwości elektryczne zawdzięcza domieszce małej ilości innych tlenków metali. Mikrostruktura warystora rozwija się podczas spiekania. Głównym elementem mikrostruktury warystora są ziarna ZnO odseparowane od siebie cienką , bogatą w bizmut, warstwą międzyziarnową. Najlepsze własności elektryczne warystor wykazuje wtedy, kiedy warstwa ta jest możliwie cienka. Jeżeli warstwa ta jest w formie aglomeratów, a w dodatku zawiera w sobie wykrystalizowany Bi2O3 lub krystality innych związków to tworzy obszar wykluczony z przewodnictwa. W warystorze o takiej strukturze w czasie przepływu prądu dochodzi do miejscowych przegrzań i zakłóceń w działaniu. W pracy udowodniono doświadczalnie, że spiekając wstępnie tlenek bizmutu z tlenkami innych metali można wpływać na kształt warstwy miedzyziarnowej, a więc i na elektryczne własności warystora. Przeprowadzone doświadczenia dowiodły, że jeżeli Bi2O3 przed dodaniem do warystora spieczemy wstępnie z tlenkami Co, Sb lub Sn to tak zmodyfikowany tlenek bizmutu sprzyja równomiernemu rozprowadzeniu domieszek w warystorze przyczyniając się do eliminacji ze struktury warystora obszarów nieaktywnych elektrycznie. Natomiast wstępne modyfikowanie tlenku bizmutu tlenkami tzw. szkłotwórczymi jak PbO, SrO i MnO nie przynosi podobnego efektu.

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Peculiarities of ZnO-based varistor ceramics doped with Ba-Bi compounds

Mielcarek W., Bernik S., Prociów K.

Prace Naukowe Instytutu Podstaw Elektrotechniki i Elektrotechnologii Politechniki Wrocławskiej. Konferencje

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2004

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Vol. 40, nr 15

158-161

EN

Varistor ceramics added with Ba-Bi and Ti is distinguished by enhanced mechanical and electrical features in comparison to the typical multicomponent ZnO ceramics. In the case of typical varistor ceramics during heating to sintering temperature forms the Bi-Sb-Zn pyrochlore phase which reacts with ZnO delivering Bi2O3 fraction in much volume. Bi2O3 volume fraction containing Bi2O3 crystallites and other secondary (spinels, pyrochlore) phases are of no importance to ZnO wet-ability or varistor a value. Just opposite, it develop tensile stresses and electrically useless areas in varistor body. The following research was intended to find the way of restricting the volume of an intergranular phase in varistor body. It was found out that when varistor ceramics is added with Bi-Ba compound, the pyrochlore phase cannot form so easy and in so much quantity, as the Ba-Bi decomposition to Bi2O3 occurs only in presence of some Ba reactant. In this case it was Ti which, as each of varistor additive, was well dispersed and present in varistor body in small quantity. What more in the case of Ba-Bi added ceramics the amount of other additives, which in typical technology are added in access, can be restricted.; As it appeared from SEM images of varistors microstructure it benefited the varistor body in better homogeneity of Bi2O3 rich intergranular phase and less quantity of secondary phases. The lower amount of secondary phases at the grain boundaries contributed to increase of effective contacts between ZnO grains In the effect also varistor electrical properties improved considerably.