Papers by Author: N.Ž Romčević

Abstract: Bismuth titanate is a typical layer-structured ferroelectric material and belongs to the Aurivilius type-structure compounds family. A bismuth titanate ceramic material could be obtained by mechanically activated synthesis after thermal treatment at a temperature slightly lower than in conventional solid-state reaction. In this case bismuth titanate was prepared through mechanochemical synthesis starting from bismuth oxide and titanium oxide in rutile form. The mixture of oxides was milled in a zirconium oxide jar in a planetary ball-mill in intervals from 1 to 12 hours. The ratio of powders to zirconium oxide balls during milling was 1:20. Bismuth titanate was formed after 1 h. The Raman spectroscopy analysis was performed.

Abstract: In Part I of this paper, we used X-ray, far-infrared reflectivity and electron paramagnetic resonance measurements to investigate optical and magnetic properties of Hg1-xMnxSe (x≤0.26) alloys. In Part II, we expand our investigation to Raman spectroscopy and galvanomagnetic measurements. We registered two-mode behaviour of long wavelength optical phonons and described it by modified Genzel’s model. Except modes from the centre of Brillouin zone, there are some of forbidden modes in Raman spectra that originate from the edge of the zone, as well as a mode that corresponds to the maximum of phonon density of states. Modes of unalloyed α–MnSe are registered, too.

Abstract: SiO2 layers were deposited by reactive d.c ion sputtering (using 1keV Ar+ ion gun) from a high purity silicon target in an oxygen ambient. The base pressure in the deposition chamber was 4.7·10-9mbar, and the substrate temperature was held at 550 °C. The argon partial pressure during ion gun operation was 1·10-3mbar. Structural characterization of the films was performed by Rutherford backscattering spectrometry (RBS analysis), electron microprobe analysis, X-ray diffraction (XRD analysis) and Raman spectroscopy. Reactive sputtering proved to be efficient for the deposition of silica at an oxygen partial pressure of 2·10-4mbar and an electrical current on the target of 5.5mA.

Abstract: In this paper we used X-ray, far-infrared reflectivity and electron paramagnetic resonance measurements to investigate the optical and magnetic properties of Hg1-xMnxSe (x£0.26) alloys. Also, we used different models to describe magnetic and phonon structure.

Abstract: Phonon spectra of Cd1-xMnxS (x = 0; 0.01; 0.05; 0.1; 0.15; 0.3) nanoparticles (d ~ 4.5 nm) have been investigated by far-infrared reflection (FIR) (spectral range 40 - 600 cm-1, temperature range 80 – 300 K) and Raman spectroscopy (100 – 700 cm-1, 300 K). Cd1-xMnxS nanoparticles have been synthesized by using aqueous solution precipitation. We obtained interesting features in FIR spectra: there are expected modes of bulk CdS (240 cm-1, 300 cm-1), new modes connected with nano-size of CdS (130 cm-1, 170 cm-1) and additional mode at 120 cm-1 in Cd1-xMnxS nanoparticles which can be assigned to the presence of Mn. The position of obtained modes is discussed in the frame of the linear chain model with both mass and force constant defects. Raman spectroscopy gives us only the mode at 300 cm-1 and its second harmonic.