Papers by Author: Jovan Blanuša

Abstract: Zn-Mn-O semiconductor crystallites with nominal manganese concentration x = 0.01, 0.02, 0.04 and 0.10 were synthesized by a solid state reaction route using oxalate precursors. Thermal treatment procedure was carried out in air at different temperatures in the range 400 - 900°C. The samples were investigated by X-ray diffraction, magnetization measurements and electron paramagnetic resonance. X-ray analysis reveals that dominant crystal phase in the Zn-Mn-O system corresponds to the wurtzite structure of ZnO. Room temperature ferromagnetism is observed in the Zn-Mn-O samples with lower manganese concentration, x ≤ 0.04, thermally treated at low temperature (500°C). Saturation magnetization in the sample with x = 0.01 is found to be 0.05 μB/Mn. The ferromagnetic phase seems to be developed by Zn diffusion into Mn-oxide grains.

Abstract: In this paper the influence of tribophysical activation on non-isothermal sintering of barium titanate has been investigated. BaTiO3 powders were tribophysically activated in a planetary ball mill for 0, 60 and 120 min., pressed and non-isothermally sintered up to 1380oC. Dilatometric analysis was performed in air in the temperature range from room temperature to 1380oC with heating rates of 10, 20 and 30oC/min. The samples were analyzed by the X-ray powder diffraction method. Investigation of the morphology of microstructure constituents was performed using the scanning electron microsocopy method. With the purpose of optimizing technological parameters the results obtained by microstructure analysis were correlated with the results of quantitative dilatometric analysis.

Abstract: Spinel samples of Li_1.33xCo_2-2xTi_1+0.67xO₄ crystallize in two space groups: Fd- 3 m for 0≤x≤0.40 and x=1, and P4₃32 for 0.50≤x≤0.875. In S.G. P4₃32 magnetic Co²⁺ ions occupy 8c sites (for x=0.75 and 0.875), or 8c, 4b and 12d sites (for x=0.50). In x=0.25 and 0.40 samples Co²⁺ occupy both 8a and 16d cation sites of the S.G. Fd- 3 m [1]. Observed differences in magnetic behaviour of the samples are induced by crystallographic distribution of Co²⁺. Possible paths for exchange interactions in S.G. P4₃32 were analysed. It was found that the superexchange is the dominant exchange mechanism where Co²⁺ (8c)-O(24e)-Co²⁺(12d) path was the most important one. On the basis of the results on crystallographic distribution we suggest x=0.50 sample as potential electrode material in Li ion rechargeable batteries.

Abstract: The ultrafine spinel NiFe_1.9M_0.1O₄ powders (M=Al, Y, Cr, Fe) were synthesized by thermal decomposition of appropriate mixtures of complex compounds with acetylacetone - (2,4 pentadione) ligands ([M(AA)_x]) at 500 °C. Samples were annealed in the temperature range 600-1000 °C and the crystallization process was followed by XRD. The largest crystallite size and the highest crystallization rate are observed for NiFe_1.9Al_0.1O₄, while the opposite was found for NiFe_1.9Y_0.1O₄. Strain value in NiFe_1.9Y_0.1O₄ changes sign at temperatures between 700-800 °C, while for NiFe_1.9M_0.1O₄ (M=Al, Cr) it has a positive sign and reaches the maximum value at 700 °C. The crystal structure of the samples annealed at 1000 °C was refined using the Rietveld profile method. Cation substitution in Ni-ferrite changes its structural and microstructural parameters, and can also significantly influence other physical properties.