Characterization of Barium Titanate Ceramic Powders by Raman Spectroscopy

Barium titanate, BaTiO3 ceramic powders were prepared by mechanochemical synthesis and by the Pechini method. A powder mixture of BaO and TiO2 was treated in a planetary ball mill in an air atmosphere for Lip to 1 h, using zirconium oxide vial and zirconium oxide balls as the milling medium. After 60 min BaTiO3 phase was formed. In both ways BaTiO3 ceramics were sintered after 2 h on 1300 degrees C without pre-calcinations step. The heating rate was 10 degrees C min(-1). The formation of phase and crystal structure of BaTiO3 was approved by X-ray diffraction analysis and the Raman spectroscopy. The morphology and microstructure of obtained powders were examined by scanning electron microscopy method. Sharp phase transition from ferroelectric to paraelectric state was observed. The hysteresis loop is very well performed with regular sharp characteristic of ferroelectric materials

Kарактеризација наночестица кобалт ферита добијених различитим методама синтезе и поређење са Рамановим спектрима других ферита и неких кубичних оксидних спинела

ingle phase cobalt ferrite (CoFe2O4) with nanoparticles of similar sizes (15.7-19 nm) was obtained by different synthesis methods: coprecipitation, ultrasonically assisted coprecipitation, coprecipitation followed by mechanochemical treatment, microemulsion and microwave assisted hydrothermal synthesis. The obtained CoFe2O4 samples have been studied using a variety of characterization techniques: X-ray diffraction (XRD), Raman spectroscopy, far infrared (FIR) reflectivity and attenuated total reflectance (ATR) in combination with Fourier-transform infrared (FTIR) spectroscopy in mid IR spectra. Different methods of synthesis produced nanoparticles with different lattice constants, internal stresses and different cation inversion values. This is confirmed in the subtle changes in the Raman and IR spectra of different CoFe2O4 nano-powders. The Raman spectra of CoFe2O4 were compared with the spectra of other ferrites and some cubic oxide spinels in an attempt to evaluate the contribution of tetrahedral and octahedral oscillations in certain Raman modes.Монофазни кобалт ферит са наночестицама сличних величина (15,7-19 нанометара) добијен је различитим методама синтезе: копреципитацијом, ултразвучно потпомогнутом копреципитацијом, копреципитацијом праћеном механохемијском синтезом, микроемулзијом и микроталасном хидротермалном синтезом. Добијени узорци кобалт ферита су проучавани коришћењем различитих техника карактеризације: дифракцијом рендгенских зрака на праху, Раман спектроскопијом, рефлексијом у далекој инфра-црвеној области (ИЦ) и методом апсорпције при вишеструкој тоталној рефлексији у комбинацији са инфра-црвеном спектроскопијом (АТР-ИЦ) у средњој инфра црвеној области. Различитим методама синтезе добијене су наночестице са различитим константама решетке, унутрашњим напрезањима и различитим вредностима инверзије катјона. Ово је потврђено у суптилним променама у Раман и ИЦ спектрима различитих нано-прахова кобалт ферита. Раман спектри кобалт ферита упоређени су са спектрима других ферита и неких кубних оксидних спинела у покушају да се процени утицај удела тетраедарских и октаедарских осцилација у одређеним Раман модовима

Photoluminescence Spectroscopy of CdTe/ZnTe Self-Assembled Quantum Dots

We present photoluminescence (PL) measurements of two different, 3 monolayers and 12 monolayers (ml), CdTe self-assembled quantum dot (SAQD) samples. The spectra were recorded in the temperature range 20 K–300 K, with photoexcitation over the ZnTe barrier layer. PL spectra displayed two main emission bands. High-energy PL emission (E1) is ZnTe LO like phonon- (ωLO = 204.2 cm−1 (3 ml), ωLO = 207.3 cm−1 (12 ml)) assisted deexcitation. Dominant low-energy band (E2) presents the direct deexcitation to ground state of the CdTe quantum dots

Vibrational and magnetic properties of nano-sized CoFe2O4 obtained by various synthesis techniques: a comparative study

Nanocrystalline CoFe2O4 has been synthesized by various synthesis methods. The obtained monodomain nanoparticles are similar in sizes (15.8-19 nm), but with different internal stresses, size distributions and cation inversion coefficients (0.51 - 0.90) due to different synthesis routes. The structure and cation distribution are investigated by XRD diffraction analysis, Raman and FIR spectroscopy. Measurement of magnetization, i.e. coercivity, enable the calculation of the anisotropy coefficient K1 = (3.6-5.12)·105 J cm-3, which is very high in cobalt ferrite. The anisotropy coefficient directly depends on the nanoparticle size. It has been shown that magnetization linearly depends on the cation inversion, except in the sample with the largest nanoparticles (19 nm), where the more regular crystal structure prevails and higher values of magnetization were obtained. The average magnetic moments at 300 K are: μFe = 3.6μB and μCo = 2.5μB. It is obvious that with small adjustments in the synthesis, desirable nanoparticle properties can be obtained

Far-infrared spectroscopy of a nanocomposite of polyvinyl alcohol and lead sulfide nanoparticles

A nanocomposite consisting of lead sulfide (PbS) nanoparticles (NPs) with average diameter of 26 angstrom, according to absorption threshold shift, and polyvinyl alcohol (PVA) was characterized using far-infrared absorption spectroscopy. The experimental results are consistent with theoretical calculations that include proper mechanical boundary conditions at the nanocrystal-host interface

Determination of Microstructural Changes By Severely Plastically Deformed Copper-Aluminum Alloy: Optical Study

Our work deals with the problem of producing a complex metal-ceramic composite using the processes of internal oxidation (IO) and severe plastic deformation. For this purpose, Cu-Al alloy with 0.4wt.% of Al was used. IO of sample serves in the first step of the processing as a means for attaining a fine dispersion of nanosized oxide particles in the metal matrix. Production technology continues with repeated application of severe plastic deformation (SPD) of the resulting metal-matrix composite to produce the bulk nanoscaled structural material. SPD was carried out with equal channel angular pressing (ECAP), which allowed that the material could be subjected to an intense plastic strain through simple shear. Microstructural characteristics of one phase and multiphase material was studied on internally oxidized Cu with 0.4wt.% of Al sample composed of one phase copper-aluminum solid solution in the core and fine dispersed oxide particles in the same matrix in the mantle region. In this manner AFM, X-ray diffraction and Raman spectroscopy were used. Local structures in plastically deformed samples reflect presence of Cu, CuO, Cu2O, Cu4O3 or Al2O3 structural characteristics, depending on type of sample

Far-infrared spectra of Hg1-xMnxTe alloys

The infrared reflection spectra of Hg1-xMnxTe with x = 0.02, 0.04, 0.08 and 0.10 have been measured at room temperature in the spectral region from 70 to 500 cm(-1). The analysis of the far-infrared spectra was made by a fitting procedure based on the dielectric function which includes spacious distribution of free carrier influence on the plasmonphonon interaction. The influence of energy gap opening (for x approximate to 0.05) on far-infrared reflection spectra was analyzed. In spite of the strong plasmon-LO phonon interaction, we found that the long wavelength optical phonon modes of these mixed crystals showed a two-mode behavior. The model of phonon behavior based on Genzels model, was developed. This theoretical model shows very good agreement with experimental results. (C) 2002 Elsevier Science B.V. All rights reserved

Far-infrared spectra of Hg1-xMnxTe alloys

The infrared reflection spectra of Hg1-xMnxTe with x = 0.02, 0.04, 0.08 and 0.10 have been measured at room temperature in the spectral region from 70 to 500 cm(-1). The analysis of the far-infrared spectra was made by a fitting procedure based on the dielectric function which includes spacious distribution of free carrier influence on the plasmonphonon interaction. The influence of energy gap opening (for x approximate to 0.05) on far-infrared reflection spectra was analyzed. In spite of the strong plasmon-LO phonon interaction, we found that the long wavelength optical phonon modes of these mixed crystals showed a two-mode behavior. The model of phonon behavior based on Genzels model, was developed. This theoretical model shows very good agreement with experimental results. (C) 2002 Elsevier Science B.V. All rights reserved

Gallium doping influence on optical and transport properties of PbTe

Zn this work we used far-infrared and Raman spectroscopy for investigation of gallium doping influence on optical and transport properties of PbTe. We focused our interest to fortify the correlation between local modes and charge state of impurity and in that way clarify the behavior of the DX-like centers in this systems.Trends in Advanced Materials and Processes, 3rd Yugoslov-Materials-Research-Society Conference, Sep 20-24, 1999, Herceg Novi, Yugoslavi

Far-infrared spectra of Pb(1-x)Mn(x)Tealloys

Far-infrared reflectivity spectra of Pb1-xMnxTe (0.0001 less than or equal to x less than or equal to 0.1) single crystals were measured in the 10-250 cm(-1) range at room temperature. The analysis of the far-infrared spectra was made by a fitting procedure based on the model of coupled oscillators. In spite of the strong plasmon-LO phonon interaction, we found that the long wavelength optical phonon modes of these mixed crystals showed an intermediate one-two mode behavior. (C) 2001 Elsevier Science B.V. All rights reserved