Zorica Ž. Lazarević

Study of NiFe2O4 and ZnFe2O4 Spinel Ferrites Prepared by Soft Mechanochemical Synthesis

Two types of ferrites, NiFe2O4 and ZnFe2O4 were prepared by soft mechanochemical synthesis. XRD and Raman spectroscopy were used to characterize the ferrite samples. On the basis of magnetic measurements was confirmed that the degree of inversion changes after sintering. The conduction activation energy, ΔE was determined by fitting the DC conductivity data with the Arrhenius relation. The effect of temperature on impedance parameters was studied using an impedance analyzer in a wide frequency range (100 Hz - 10 MHz). It was observed that the impedance spectra of NiFe2O4 and ZnFe2O4 ferrites include both grain and grain boundary effects.

Raman spectroscopy of bismuth silicon oxide single crystals grown by the Czochralski technique

In this work, single crystals of bismuth silicon oxide (BSO; Bi12SiO20) have been grown by the Czochralski method. The growth conditions were studied. The critical diameter and the critical rate of rotation were calculated. Suitable polishing and etching solutions were determined. The structure of the Bi12SiO20 has been investigated by x-ray diffraction (XRD), and Raman and Fourier transform infrared spectroscopy (FTIR) spectroscopy. The results obtained are discussed and compared with the published data. The pale yellow Bi12SiO20 single crystals prepared were without cores. Using spectroscopic measurements 19 Raman and 5 IR modes were observed.

Spectroscopic characterization of YAG and Nd:YAG single crystals

In this paper, we used the Czochralski method to obtain good quality yttrium aluminium garnet (YAG, Y3Al5O12) and yttrium aluminium garnet doped with neodymium (Nd:YAG) crystals. The investigations were based on the growth mechanisms and the shape of the liquid/solid interface crystallization front on the crystal properties and incorporation of Nd3+ ions. The obtained single YAG and Nd:YAG crystals were studied by use of x-ray diffraction, Raman and IR spectroscopy. There are strong metal oxygen vibrations in the region of 650–800 cm−1 which are characteristics of Al-O bond: peaks at 784/854, 719/763 and 691/707 cm−1 correspond to asymmetric stretching vibrations in tetrahedral arrangement. Peaks at 566/582, 510/547 and 477/505 cm−1 are asymmetric stretching vibrations and 453/483 cm−1 is the symmetric vibration of the Al-O bond in octahedral arrangements of the garnet structure. Lower energy peaks correspond to translation and vibration of cations in different coordinations—tetrahedral, octahedral and dodecahedral in the case of the lowest modes.

Study of Structure and Properties of Bi4Ti3O12 Prepared by Mechanochemical Syntheses

Bi 4 Ti 3 O 12 powder was synthesized from bismuth oxide and titanium oxide. Mixture of oxides was milled in zirconium oxide jar in the planetary ball-mill during 1, 3 and 6 h. Extended time of milling directed to formation of higher amount of titanates perovskite phase. Bi 4 Ti 3 O 12 was formed between 1 and 3 h of milling time. The phase formation of Bi 4 Ti 3 O 12 , crystal structure and powder particle size were followed by XRD, Raman spectroscopy and SEM analysis. After milling for various times the powders were compacted by pressing and isothermal sintering. Sample milled for 3 h and subsequently sintered at 1000°C for 24 h exhibit a hysteresis loop, confirming that the synthesized material possesses ferroelectric properties. All results affect that the structure Bi 4 Ti 3 O 12 is strongly dependent on the milling time.

Far-infrared investigations of the surface modes in CdS thin films

The properties of Cadmium sulphide (CdS) thin films were investigated by applying atomic force microscopy (AFM) and far–infrared spectroscopy. CdS thin films were prepared using thermal evaporation technique under a base pressure of 2 × 10−5 torr. The quality of these films was investigated by AFM spectroscopy. We apply far–infrared spectroscopy to investigate the optical properties of CdS thin films, and reveal the existence of a surface optical phonon (SOP) mode at 297 cm−1. For the first time, the dielectric function of CdS thin film is modeled as a mixture of homogenous spherical inclusions in air by the Maxwell–Garnet formula. In the analysis of the far–infrared reflection spectra, a numerical model for calculating the reflectivity coefficient for a system which includes films and substrates has been applied.

Structural Properties of Cu-Se-CuSe 2 Thin Films

This paper describes the structural and optical properties of Cu-Se-CuSe2 thin films. The surface morphology of thin films was investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Formation of thin films is concluded to proceed unevenly, in the form of islands which later grew into agglomerates. The structural characterization of Cu-Se-CuSe2 thin film was investigated using X-ray diffraction pattern (XRD). The presence of two-phase system is observed. One is the solid solution of Cu in Se and the other is low-pressure modification of CuSe2. The Raman spectroscopy was used to identify and quantify the individual phases present in the films. Red shift and asymmetry of Raman mode characteristic for CuSe2 enable us to estimate nanocrystal dimension. In the analysis of the far-infrared reflection spectra, numerical model for calculating the reflectivity coefficient of layered system, which includes film with nanocrystallite inclusions (modeled by Maxwell–Garnet approximation) and substrate, has been applied. UV–VIS spectroscopy and photoluminescence spectroscopy are employed to estimate direct and indirect band gap of CuSe2.

Study of Nanodimensional Spinel Ni 0.5 Zn 0.5 Fe 2 O 4 Ferrite Prepared by Mechanochemical Synthesis

The nanodimensional Ni0.5Zn0.5Fe2O4 ferrites were prepared from mixture of NiO/ZnO/α-Fe2O3 and Ni(OH)2/Zn(OH)2/Fe(OH)3 powders by (soft) mechanochemical synthesis after 5 and 10 h of milling time. The XRD of the sample obtained after 10 h milling time shows single phase cubic spinel structure. TEM analysis revealed that all samples are composed of more or less agglomerated nanosize particles. The average size of nano crystallites is ~20 nm. The degree of the cation inversion of NZF is estimated for spinel fraction in all samples by Rietveld analysis. In the Raman spectra are observed all of first-order active modes. In the spectra of the single phase “hydroxide” samples it is visible that the energy position and intensity of modes is dependent on the composition and cation distribution. It was shown that the modes in Raman spectra of nickel-zinc ferrite that originate from vibrating of different cations could be clearly distinguished. From the ratio of intensities of the A 1g-type Raman modes, it is possible to estimate the inversion of cations. The Mossbauer spectra were fitted by several subspectra and according to known subspectral areas of both iron sites the degree of inversion was calculated, also. The cation inversion is λ = 0.36(3) for ferrite sample obtained from the mixture of appropriate hydroxide for 10 h milling.

Structural, Electrical Conduction and Dielectric Studies of Mechano-synthesized Manganese Nanoferrite

In this paper, we have investigated the structural, electrical and dielectric properties of nanostructured manganese ferrite of 49 nm grain size, synthesized by mechanochemical technique. The structural studies have been made by using the X-ray diffraction, TEM and Raman spectroscopy, which confirmed the formation of spinel phase and nanostructure of prepared MnFe2O4. The electrical measurements were made in the frequency range 102–106 Hz at different temperatures between 25 and 175 °C. The temperature dependence of DC conductivity satisfies the Arrhenius relation, which indicates the semiconducting nature of sintered sample. The drift mobility was estimated from the DC conductivity measurement and it has been found that the temperature dependent. Analysis of the experimental AC electrical conductivity data shows that correlated barrier hopping mechanism is the most probable mechanism of conduction for prepared manganese ferrite. The dielectric permittivity and loss tangent of MnFe2O4 decrease with increase in frequency, while these parameters increase with increasing temperature. Such dielectric behavior is explained by using the mechanism of polarization process, which is correlated to hopping of charge between Fe2+ and Fe3+ ions as well as between Mn2+ and Mn3+ ions at octahedral sites.

Optical Properties and Electron–Phonon Interactions of CdTe1-XSex(In) Single Crystal

The far-infrared reflectivity spectra of CdTe0.97Se0.03 and CdTe0.97Se0.03(In) single crystals were measured at different temperatures. The analysis of the far-infrared spectra was carried out by a fitting procedure based on the dielectric function which includes spacious distribution of free carrier as well as their influence on the plasmon–phonon interaction. We found that the long wavelength optical phonon modes of CdTe1-xSex mixed crystals exhibit a two-mode behavior. The local In mode at about 160 cm−1 is observed. In both samples, a surface layer with a low concentration of free carriers is formed.

Structural and Optical Studies of Oxide Single Crystals Grown by the Czochralski Method

In this paper, we used the Czochralski method to obtain good-quality yttrium aluminium garnet (Y3Al5O12)—YAG and yttrium aluminium garnet doped with neodymium—Nd:YAG crystals. The investigations were based on the growth mechanisms and the shape of the liquid/solid interface on the crystal properties and incorporation of Nd3+ ions. The obtained single YAG and Nd:YAG crystals were studied by use of Raman and IR spectroscopy. There are strong metal oxygen vibrations in region 650–800 cm−1 which are characteristics of Al–O bond: peaks at 784/854, 719/763 and 691/707 cm−1 correspond to asymmetric stretching vibrations in tetrahedral arrangement. Peaks at 566/582, 510/547 and 477/505 cm−1 are asymmetric stretching vibrations, and 453/483 cm−1 is symmetric vibration of Al–O bond in octahedral arrangement of garnet structure. Lower energy peaks correspond to translation and liberation of cations in different coordinations—tetrahedral, octahedral and dodecahedral in the case of the lowest modes.