BaTiO
3 powders from sol-gel derived gels were prepared using two different drying methods. In addition to the conventional drying of gels in air at 90°C the supercritical CO
2 drying method was also ...used. Results showed that the properties of BaTiO
3 powder produced by supercritical drying with CO
2 are better. The grain surface is less contaminated as a result of the supercritical drying and the microstructure development during sintering leads to a homogeneous fine-grained microstructure.
Two different drying methods, conventional drying of gels in air at 90 C and supercritical CO2 (SC-CO2) drying, were used to prepare BaTiO3 powders from sol-gel derived gels. The results reveal that ...powders prepared by supercritical drying with CO2 are less contaminated with the organic disintegration products which are formed during drying. Sintering of a sample prepared from the CO2-dried powder leads to a homogeneous and fine-grained microstructure. 6 refs.
The PTCR effect was investigated in the ferroelectric BaNb2O6 phase (prepared by calcination of BaCO3 and Nb2O5) doped with TiO2. Composite ceramics formed after sintering in a reducing atmosphere ...and subsequent reoxidation show the PTCR effect at around 70 and 300 C, respectively. Both PTCR anomalies are associated with the formation of high resistivity grain boundaries after controlled oxidation of reduced constituent phases. 6 refs.
A new hydroxylammonium compound (NH
3OH)
2SiF
6, has been synthesized by the addition of solid NH
3OHF to an aqueous solution of H
2SiF
6. The compound was characterized by chemical analysis and ...X-ray powder diffraction, the thermal decomposition was studied by thermal analysis and mass spectrometry. (NH
3OH)
2SiF
6 crystallizes triclinic. Four endothermic peaks have been observed on the DSC curve, the decomposition products are HF, NH
3OHF and SiF
4 and the weight loss at 500°C is nearly 100%.
Donor-doped BaTiO^sub 3^ ceramics (0-0.6 mol% Nb) were investigated during the sintering process at an oxygen partial pressure of 2.4 Pa and at a maximum temperature of 1430^sup ^C. The occurring ...oxygen exchange with the ambient atmosphere was monitored quantitatively by oxygen coulometry. The coincidence between the grain growth behavior and the occurrence of distinct oxygen release peaks during the anomalous grain growth reveals that significant amounts of the donor are incorporated and charge-compensated by electrons only under the conditions of the anomalous grain growth. Quantitative analysis of the coulometric data shows that at a doping level of 0.2 mol% nearly all donors are charge-compensated by electrons. With increasing Nb concentration also Ti vacancies gradually begin to serve for compensation. At 0.5 mol% Nb their influence reaches 70 % of the electronic compensation.PUBLICATION ABSTRACT
MnZn-ferrite nanoparticles with a narrow size distribution were prepared in situ in water-CTAB-hexanol microemulsions using a two-step process: the precipitation of the corresponding hydroxides, ...followed by the oxidation of the Fe2+. The influence of the temperature and the time of the precipitation step was systematically studied.
