M. Taibi

Magnetic properties of the perovskite compounds YFe1–xCrxO3 (0.5≤x≤1)

Abstract Powder oxides with the formula YFe 1– x Cr x O 3 (0.5≤ x ≤1) have been studied. The samples have been prepared using the ceramic solid state reaction in air. The X-ray diffraction spectra indicated that the samples crystallise in the perovskite structure with orthorhombic deformation. The magnetic properties of these materials are concentration and temperature dependent. Zero-field-cooled and field-cooled magnetization curves show strong irreversibilities and complex hysteresis loops. The saturation magnetization for the mixed compounds shows a unusual behaviour. The results are discussed by considering the existence of many weak ferromagnetic components induced by the random distribution of the transition metal cations in the octahedral site. This leads to frustration interactions and short-range order that smooth the phase transition.

Infrared and Dielectric Studies of [(C2H5)4N]2SiF6

The infrared spectrum of [(C2H5)4N]2SiF6 was recorded and discussed in relation to its crystal structure. This spectrum indicates that cations and anions are distorted and are not hydrogen bonded. Two structural phase transitions were observed in the tetraethylammonium compound [(C2H5)4N]2SiF6 by means of dielectric measurements. High-frequency dielectric dispersion phenomena in this compound were also analysed. The evolution of the dielectric constant with the temperature indicates the presence of two phase transitions, at high temperatures, which are of order-disorder character.

One step electrodeposited CZTS thin films: Preparation and characterization

Cu2ZnSnS4 (CZTS) thin films were successfully prepared using a single-step electrodeposition process in aqueous ionic solution, followed by the sulfurization in elemental sulfur vapor ambient at different annealing temperatures and under Argon atmosphere. The structural, morphological, compositional and optical properties of the samples have been investigated. Raman spectroscopy and X-ray diffraction (XRD) have confirmed the Kesterite structure of CZTS films sulfurized at 500 °C. The chemical composition was determined by Rutherford Back Scattering (RBS) and energy dispersive X-ray spectroscopy (EDS) that show the formation of near stoichiometric CZTS thin films. The surface morphology of the samples was examined using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Optical properties of the CZTS thin film were studied by photoluminescence spectroscopy (PL).

Role of copper ions in dielectric and structural investigations of lead– borate glasses

ABSTRACT Glasses in the system 0.1CuO-(x-0.1)PbO-(1-x)B2O3 (0.3≤ x ≤ 0.7) were synthesized by using the melt quench technique. A number of studies such as X-ray diffraction (XRD), differential scanning calorimetry (DSC), fourier-transform infrared (FTIR) and Raman spectroscopy, electron paramagnetic resonance (EPR) and dielectric properties (viz., dielectric constant ϵ΄, dielectric loss and ac conductivity σac) are employed to characterize the glasses. The amorphous nature of the glasses was confirmed using XRD while the glass transition temperature (Tg) of glass samples have been estimated from DSC investigation and found that the Tg decreases with increasing PbO content. Raman and FTIR spectroscopy reveals that when increasing lead ions, the tetrahedral [BO4] units are gradually replaced by trigonal [BO3] units. The EPR study leads to determine the local site of Cu2+ ions and its transformation with the Pb content in the studied glasses.

Glass-forming region, structure and some properties of potassium manganese phosphate glasses

ABSTRACT The glass-forming region in the K2O–MnO–P2O5 ternary system was determined and the amorphous nature of the synthesized material was confirmed by X-ray diffraction. Glasses with composition (50-x)K2O-xMnO-50P2O5 (0 ≤ x ≤ 40 mol%) have been studied. Their physical, thermal and spectroscopic properties such as density, molar volume, glass transition temperature infrared and Raman spectroscopies have been investigated to understand the structural role of MnO in studied samples. The density and glass transition temperature increase with the substitution of MnO for K2O. Fourier-Transform Infrared and Raman spectroscopies reveal the depolymerization of the phosphate chains and formation of P–O–Mn bonds by the incorporation of MnO. The formation of P–O–Mn bonds, which replace P–O−···K+ bonds is in accordance with the variation of glass transition temperature (Tg), molar volume (Vm) and density (. The former bonds are the origin of the partial glass-forming ability of Mn2+. A structural model is proposed to explain the experimental results.

Electrical and structural analysis of xPbO-(1-x)B2O3 (0.3≤ x≤ 0.9) glasses

Abstract Different xPbO–(1–x)B2O3 glasses were prepared by conventional melting method. They were investigated by differential scanning calorimetry (DSC), Raman and IR spectroscopy. The glasses structure and the PbO role to the formation of the borate units in the framework is investigated. The dielectric constant and dielectric loss were measured at different frequencies and as a function of the temperature. The electrical measurements carried out showed semiconductor behavior of the conductivity as a function of temperature. The activation energies (Ea) for the conduction process indicated a thermally activated hopping mechanism. The calculated Ea values are typically 0.67–2.46 eV.

Thermal, spectroscopic and dielectric investigation of Na2–2xLi2xPbP2O7 glasses

ABSTRACT The Na2–2xLi2xPbP2O7 glasses were elaborated using the usual melting method. The amorphous system was analyzed by X-ray diffraction. The effects of the substitution of the Na+ ions by the Li+ ones on glass transition temperature, crystallization temperature and thermal stability were investigated using differential scanning calorimetry. The kinetics parameters such as activation energy Ea of the glass crystallization, the activation energy for crystal growth EG, Avrami exponent n and factor depending on the growth morphology during the process of crystallization m were determined using different models. The IR and Raman spectra are examined in order to show the influence of the composition on the vitreous structure. The dielectric studies were conducted as a function of temperature and frequencies to evaluate the composition effect on the dielectric constant, dielectric loss and ionic conductivity.

Investigation of structural and physical properties of xSrO-(100-x)P2O5 glasses

ABSTRACT The structural and physical properties for xSrO-(100-x)P2O5 glasses, with x = 30, 35, 40, 45, and 50, were investigated. The amorphous state of samples was verified by X-ray diffraction (XRD). Substitution of P2O5 for SrO in the binary SrO–P2O5 glass decreases the molar volume and increase the density measurements from 1.98 to 4.01 g/cm3. The Infra-Red (IR) and Raman spectra allow us to identify the network modifier role of Sr2+ ions and the structural network of these phosphate glasses which consists of branching (Q3), middle phosphate tetrahedra (Q2) and pyrophosphate (Q1).

Non-collinear magnetic ordering in the perovskite compound YFe1/4Cr3/4O3

Abstract The polycrystalline compound YFe0.25Cr0.75O3, prepared by solid reaction in air exhibits the perovskite structure with orthorhombic deformation. Its space group is Pbnm. High temperature d.c. magnetic susceptibility and magnetization studies have been carried out. The measurements revealed non-collinear magnetic behaviour. The occurrence of hysteresis loops and compensation effects suggests ferrimagnetic arrangements. The results are explained qualitatively assuming the presence of two uncompensated weak ferromagnets. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves merge at a temperature well above the Neels one. This suggests the occurrence of short-range magnetic order, which is induced by frustration effects. The frustration in this case results from the structural disorder due to the random distribution of the magnetic ions in the octahedral sites of the lattice.

Effect of ITO and Mo coated glass substrates on electrodeposited Cu 2 ZnSnS 4 thin films

Cu2ZnSnS4 (CZTS) thin films were elaborated at room temperature on ITO and Mo coated glass substrates using electrodeposition route, followed by a sulfurization treatment. We investigated the effect of the substrates on crystallographic structure, morphology, composition and optical properties of electrodeposited CZTS thin films. X-ray diffraction and Raman analysis showed that the deposited films were polycrystalline with kesterite structure. Film composition and surface morphology have been analyzed using Scanning electron microscopy and Energy dispersive analysis. Photoluminescence spectroscopy showed for both films a broad PL band centered around 1.5 eV.