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Powdery nickel ferrite, NiFe2O4 has been obtained by soft mechanochemical synthesis in a planetary ball mill. Ni(OH)2 and Fe(OH)3 are used as initial compounds. This mixture was mechanically activated for 25h, uniaxial pressed and sintered at 1100 °C for 2h. The phase composition of the sintered sample was analyzed by X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and Raman spectroscopy. Morphologies were examined by scanning electron microscopy (SEM). The electrical DC/resistivity/conductivity at different temperatures was measured using a Source Meter Keithley 2410. An Impedance/Gain-Phase Analyzer (HP-4194) was used to measure the impedance spectra (100Hz -10MHz) at different temperatures. [ABSTRACT FROM AUTHOR]

Nanocrystalline samples of ZnO(Mn) were synthesized by hydrothermal method. The morphology of the samples was studied by HRTEM and SEM. X-ray diffraction was used to determine composition of the samples (ZnO and ZnMn 2 O 4 ) and the mean crystalline size (from 16 to 99 nm). In this paper we report the experimental spectra of Raman scattering (from 100 to 1600 cm −1 ) with surface optical phonons (SOP) in range of 497–538 cm −1 as well as formation of new phases MnO, Mn 3 O 4 and ZnMnO 3 . The phonon of registered phase's exhibit effects connected to phase concentration, while the SOP phonon mode exhibit significant confinement effect. [ABSTRACT FROM AUTHOR]

Nanocrystaline samples of ZnO(Fe) were synthesized by traditional wet chemical method followed by calcinations. Samples were characterized by X-ray diffraction to determine composition of the samples (ZnO, ZnFe 2 O 4 and Fe 2 O 3 ) and the mean crystalline size (from 8 to 51 nm). In this paper we report the experimental spectra of Raman scattering (from 200 to 1600 cm −1 ) with surface optical phonons (SOP) in range of 500–550 cm −1 . The phonon of registered phase’s exhibit effects connected to phase concentration, while the SOP phonon mode exhibit significant confinement effect. [ABSTRACT FROM AUTHOR]

Highlights: [•] ZnO doped with MnO, samples prepared by calcination method. [•] Coexistence of phases Mn3O4, ZnMn2O4 and ZnMnO3 with ZnO registered by Raman spectroscopy. [•] Existence of ZnO nanoparticles surface optical phonon. [Copyright &y& Elsevier]

Abstract: Surface optical phonons (SOP) were observed in the range of 496–572cm−1 on Raman scattering spectra of nanocrystalline samples of ZnO(Co) prepared by use of the microwave assisted hydrothermal synthesis and traditional wet chemistry method followed by calcinations. The phase composition of the samples (ZnO, Co3O4, ZnCo2O4) and the mean crystalline size (14–300nm) were determined using X-ray diffraction measurements. The SOP phonon mode exhibit significant size confinement effect, while the phonons of registered phases exhibit effects connected to phase concentration. [Copyright &y& Elsevier]

Abstract: New semimagnetic semiconductor Hg0.91Mn0.09Te-MnSe mixture, grown by Bridgman method, was investigate by Atomic Force Microscopy, X-ray and far-infrared spectroscopy, in order to obtain the necessary feedback information to determine the optimal conditions for crystal growth. The investigated mixture consists of MnSe nanoclasters randomly distributed in Hg0.91Mn0.09Te matrix. Far-infrared reflectivity spectrum of the Hg0.91Mn0.09Te-MnSe mixture was measured in the 80–500cm−1 range at a room temperature. The analysis of the far-infrared spectrum was made by the fitting procedure. The Maxwell-Garnett effective medium theory is used for modeling an effective dielectric function, and on that way calculating both electron and phonon response. [Copyright &y& Elsevier]

We have studied the magnetic properties of nanocrystals of ZnO:MnO prepared by traditional wet chemistry method. The detailed structural and morphological characterization was performed. The results of systematic measurements of AC magnetic susceptibility as a function of temperature and frequency as well as DC magnetization are reported. We observed two different types of magnetic behavior depending on the concentration doping. For samples with low nominal content (up to 30 wt% of MnO), superparamagnetic behavior was observed. We attribute the observed superparamagnetism to the presence of nanosized ZnMnO 3 phase. For nanocrystals doped above nominal 60 wt% of MnO ferrimagnetism was detected with T C at around 42 K. This magnetic behavior we assign to the presence of nanosized Mn 3 O 4 phase. [ABSTRACT FROM AUTHOR]

Influence of laser power on nanocrystalline samples of ZnO(Co) prepared by commonly used wet chemistry method followed by calcination was investigated. Previous confirmation of the existence of ZnO and Co 3 O 4 phases was based on the X-ray diffraction measurements. Here we report the experimental spectra of non-resonant Raman scattering in the range between 100 cm −1 and 1600 cm –1 , for a series of samples irradiated with four different laser power densities. The laser power density has different influence on relative intensity of peaks that belong to ZnO phase than on those corresponding to Co 3 O 4 phase. Both peak types show characteristic broadening and red shift toward lower frequencies. The laser power densities used in our study did not cause thermal destruction in any of the investigated samples. Laser-induced local heating effects in samples caused formation of cobalt dimers on the surface of Co 3 O 4 . [ABSTRACT FROM AUTHOR]

ZnS nanoparticles were synthesized mechanochemically by high-energy milling. In order to investigate influence off milling time to sample properties, samples were produced in three different milling times (5 min, 10 min and 20 min). The morphology of samples has been investigated by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). X-ray diffraction (XRD) investigation of synthesized nanocrystals identified cubic structure. From XRD, ZnS size of crystallites was estimated as 1.9 nm (after 5 min milling time), 2.3 nm (10 min) and 2.4 nm (20 min), implying that we are in strong confinement regime. The optical properties were studied by Raman spectroscopy, in spectral region 100–500 cm −1 , excitation source was 514.5 nm ( E L = 2.41 eV), which means that we are in off resonant regime. Dominant spectral structures, of comparable intensity, are registered in spectral region 130–180 cm −1 , around 265 cm −1 and around 345 cm −1 . First two are assigned as second-order ZnS modes. A theoretical model of continuum medium was used to calculate frequencies of the confined optical phonons in ZnS. Satisfactory agreement with experimental results was found and mode at 345 cm −1 is assigned as LO type phonon confined in ZnS nanocrystal. [ABSTRACT FROM AUTHOR]

Abstract: The aim of the present work is to study the magnetic properties of nanocrystals of ZnO(Co) prepared by two methods of synthesis. We used the microwave assisted hydrothermal synthesis and traditional wet chemistry method followed by calcination. The detailed structural characterization was performed by means of X-ray diffraction and micro-Raman spectroscopy measurements. The magnetic properties were studied by means of AC susceptibility χ. All samples demonstrated Curie–Weiss behavior at higher temperatures. For calcination process, the negative values of the Curie–Weiss θ temperature were observed indicating the predominance of antiferromagnetic interactions. For samples prepared by hydrothermal synthesis, we observed the breakdown of predominance of antiferromagnetic interactions. [Copyright &y& Elsevier]

Abstract: Far-infrared reflectivity spectra, in spectral region 50–600cm−1 and temperature region 80–300K, of CdS and Cd1−x Mn x S nanocrystals embedded in hexametaphosphate, are presented. The analysis of the far-infrared experimental reflectivity spectrum was made by the fitting procedure. The Maxwell–Garnet effective medium theory is used for modeling an effective dielectric function as well as to separate respond from nanoparticles. To analyze spectra in CdS ω TO(≈238cm−1) to ω LO(≈305cm−1) spectral region, quantized dipolar modes in a spherical isotropic material quantum dot (QD) are considered in the framework of a continuum model. As to the mechanical boundary conditions rigid sphere is concerned. Experimental far-infrared reflectivity spectra of our samples are in general agreement with the predictions of this model. Experimentally registered and through fitting procedure located features for CdS nanoparticles in spectral region below CdS ω TO at: ≈102cm−1, ≈135cm−1, ≈170cm−1 and ≈210cm−1 are associated to defect induced modes, especially to defects located near the surface of CdS QD. In region over CdS ω LO, modes are identified as multiphonons. In Cd1−x Mn x S QD spectra new reflectivity peaks are at: ≈85cm−1, ≈110cm−1 and ≈180cm−1 in spectral region below CdS ω TO, ≈270cm−1 inside CdS ω TO–ω LO spectral region and ≈356cm−1 and ≈376cm−1 in region over CdS ω LO. First two registered modes are associated to both mass and force constant defects at the surface, and rest four modes are consequence of MnS phases present in the sample. [Copyright &y& Elsevier]

Abstract: The aim of the present work is to study the magnetic properties of ZnO(Fe) nanocrystalline samples prepared by two methods of synthesis. We have used the microwave assisted hydrothermal synthesis and traditional wet chemistry method followed by calcination. The detailed structural characterization was performed by means of X-ray diffraction and micro-Raman spectroscopy measurements. The dynamic magnetic properties were studied by means of AC susceptibility χ. The measurements were performed at small AC magnetic field with amplitude not exceeding 5Oe and different frequency values (from 7Hz to 9970Hz). The AC susceptibility maxima have been found for in-phase susceptibility Re(χ) and for out of phase susceptibility Im(χ). We analyzed the observed frequency dependence of the peak temperature in the AC susceptibility curve using the empirical parameter Φ that is a quantitative measure of the frequency shift and is given by the relative shift of the peak temperature per decade shift in frequency, as well as Vogel–Fulcher law. [Copyright &y& Elsevier]

Abstract: Nanocrystaline samples of ZnO(Fe) were synthesized by wet chemical method. Samples were characterized by X-ray diffraction to determine composition of the samples (ZnO, Fe2O3, ZnFe2O4) and the mean crystalline size (8–52nm). In this paper we report the experimental spectra of Raman scattering. Main characteristics of experimental Raman spectrum in 200–1600cm−1 spectral region are: sharp peak at 436cm−1 and broad two-phonon structure at ∼1150cm−1, typical for ZnO; broad structure below 700cm−1 that has different position and shape in case of ZnFe2O4 or Fe2O3 nanoparticles. Low-frequency Raman modes were measured and assigned according to confined acoustic vibrations of spherical nanoparticles. Frequencies of these vibrational modes were analyzed in elastic continuum approximation, which considers nanoparticle as homogeneous elastic sphere. [ABSTRACT FROM AUTHOR]