Papers by Author: Darko Makovec

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Authors: Tatiana Plutenko, Oleg V'yunov, Dmytro Plutenko, Anatolii Belous, Darko Makovec
Abstract: Conditions for the formation of (1-x)BaTiO3xLi0.5Bi0.5TiO3 (0 ≤ x ≤0.6) solid solutions with positive temperature coefficient of resistance (PTCR) effect were studied. Solid solutions were prepared by solid state reaction technique. Samples were sintered under reducing atmosphere N2/H2 in the temperature range 1200–1450 °C with subsequent oxidation in air. The phase composition was investigated by X-ray powder diffraction method. It was found that samples of (1-x)BaTiO3xLi0.5Bi0.5TiO3 (0 ≤ x ≤0.6) solid solutions at room temperature exhibit perovskite structure. Unit cell parameters of unstable at the room temperature compound Li0.5Bi0.5TiO3 were determined by extrapolation of concentration dependence of the unit cell parameters in the (1-x)BaTiO3xLi0.5Bi0.5TiO3 system. It was shown that minimum value of resistivity ρmin rises with increase in x value. Complex impedance method shown that ceramic grains of (1-x)BaTiO3xLi0.5Bi0.5TiO3 materials consist of three areas with different electrical properties. Boundary and outerlayer region of grains make the main contribution to the PTCR effect in lithium-containing solid solutions. It was shown that magnitude of the potential barrier's decreases with increasing x.
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Authors: Irena Pibošič, Darko Makovec, Miha Drofenik
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Authors: Aljoša Košak, Darko Makovec, Miha Drofenik
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Authors: S. Marković, V.Z. Pejovic, M. Mitrić, N. Cvjetićanin, Darko Makovec, Dragan P. Uskokovic
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Authors: Miha Drofenik, M. Kristl, Darko Makovec, Aljoša Košak
Abstract: Sonochemically assisted co-precipitation has been used to prepare nanosized manganesezinc- ferrite powder. A suspension of constituent hydroxides was ultrasonically irradiated for various times with high-intensity ultrasound radiation (20 kHz, 750 W) using a direct-immersion titanium horn. The average grain size and magnetization of the synthesized MnZn-ferrite nanoparticles gradually increases with the time of ultrasonic irradiation.
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Authors: Miha Drofenik, Darko Makovec, Aljoša Košak, M. Kristl
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Authors: V. Uskoković, Darko Makovec, Miha Drofenik
Abstract: Nanostructured lanthanum-strontium manganites have been synthesized using two different co-precipitation approaches, one in bulk solution, and the other in reverse micelles of CTAB/1-hexanol/1-butanol/water microemulsion. In both cases, precursor cations were precipitated by alkali precipitating agents. The properties of the material synthesized by using these two methods were compared in order to reveal potential advantages of microemulsion-assisted approach. The influence of the annealing conditions on the properties of synthesized manganites was investigated by using X-ray diffraction, transmission electron microscopy, differential thermal analysis, thermogravimetric analysis and magnetic measurements.
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Authors: Aljoša Košak, Darko Makovec, Miha Drofenik
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.
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Authors: Nina Ule, Darko Makovec, Miha Drofenik
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Authors: Miha Drofenik, Darja Lisjak, Darko Makovec
Abstract: Magnetic nanoparticles are materials of great interest because of the remarkable fundamental properties exhibited by these materials as well as their technological potential in the area of biomedicine and other areas. The technologically useful properties of magnetic nanomaterials are not limited to their structural, chemical or mechanical behaviour, but also involve the phenomena that arise from their finite size and the surface effects that dominate the magnetic behaviour of individual nanoparticles. New techniques that have been developed recently have permitted researchers to produce larger quantities of nanomaterials and characterize them better. Here, some of the most promising procedures are reported, including techniques based on hydrothermal syntheses, sol-gel syntheses, co-precipitation syntheses, mechanochemical syntheses, sonochemical syntheses, spray pyrolysis and microemulsion-assisted syntheses.
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