Volume 12, Num 2 article 11

Monte Carlo study of the possibility of two compensation points in a ferrimagnetic core/shell nanoparticle Ising model

Ahmed ZAIM and Mohamed KEROUAD

Monte Carlo simulation has been used to study the magnetic properties and the critical behaviors of a single spherical nanoparticle, consisting of a ferromagnetic core of spin-1/2 surrounded by a ferromagnetic shell of spin-3/2 with antiferromagnetic interface coupling, located on a simple cubic lattice. We find a number of characteristic phenomena. In particular, the effects of the shell coupling and the interface coupling on both the critical and compensation temperatures are investigated. We have found that, for appropriate values of the system parameters, two compensation temperatures may occur in the present system.

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Keyword: Nanoparticles, Compensation point, Ising model, Monte Carlo simulations.

PACS : 75.50.Tt, 75.40.Mg, 75.75.+a, 05.10.Ln

Laboratoire Physique des Matériaux et Modélisation des Systèmes (LP2MS) (Unité Associée au CNRST-URAC),  Faculty of  Sciences, B.P. 11201 Meknes, Zitoune, Morocco.
E-mail: ah_zaim@yahoo.fr

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Volume 12, Num 2 article 12

Phase diagram of TTB ferroelectric compounds Pb_1−xK_2xNb₂O₆

E.Choukri¹, Y. Gagou², D. Mezzane¹, M. Elmarssi², Z.Abkhar¹, M. Elaatmani³, I. Luk’yanchuk² and P. Saint-Grégoire⁴

Substitution of Pb with K in the PbNb₂O₆ phases leads to a new composition of solid solution with chemical composition Pb_1−xK_2xNb₂O₆ with x ranging from 0 to 0.34 in steps of 0.05. Ferroelectric ceramics were synthesized using solid state reaction between the corresponding oxides and carbonates. Powders are pressed and heated into ceramics and their compaction is about 92%. The tetragonal tungsten bronze (TTB) structure at room temperature was confirmed by X-ray diffraction (XRD). The temperature dependence of dielectric permittivity was measured from 35 to 600°C in the 20-106 Hz frequency range.
Transition temperature decreases with the lead concentration while from x=0, with Tc=600°C and to x=0.3 with Tc=388°C.  These measurements permit to present a basical phase diagram of this family compound showing the evolution of the characteristic transition temperature Tc versus temperature. The behaviour of Tc is in agreement with theoretical study of the ferroelectric phase transition in TTB using Monte Carlo (MC) simulation. The dielectric properties of these ceramics are similar to those obtained on a single crystal and illustrate the quality of preparative conditions.

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Keyword: ferroelectric, tetragonal tungsten bronze, phase transition, dielectric permittivity.

1 LMCN, F.S.T.G.University Cadi Ayyad Marrakech, Morocco.
2 LPMC, Université de Picardie, 33, rue Saint-Leu, 80039 Amiens Cédex, France.
3 F.S.S. University Cadi Ayyad Marrakech, Morocco.
4 L2MP, UMR-CNRS 6137, Université de Toulon-Var, BP 132, 83957 La Garde Cédex, France.

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Volume 12, Num 2 article 13

Dielectric Properties Of Lead Potassium Lithium Niobate (Pb1,85K1,15Li0,15Nb5O15) With Tetragonal Tungsten Bronze (TTB) Type Structure

E.Choukri¹, Z.Abkhar¹, Y. Gagou², M.-A. Frémy³, J.-L. Dellis², D. Mezzane¹, M. Elmarssi², I. Luk’yanchuk² and P. Saint-Grégoire³

A new tungsten bronze ceramic oxide, Pb2-xK1+xLixNb5O15 (PKLN) (x =0.15) was prepared by high temperature solid-state reaction route. Structural and electrical properties are investigated using X-ray diffraction and dielectric measurements. Room temperature XRD pattern confirms the formation of the compound with an orthorhombic crystal system. The dielectric permittivity and the loss tangent of the sample have been measured in a frequency range 1Hz–1MHz and a temperature range 35–550 °C.
Studies of dielectric properties show that the compound exhibits an anomaly at 425°C (usually called transition temperature).The electrical parameters of the material were studied using complex impedance spectroscopy showing that the compound exhibits non-Debye of relaxation process. In the paraelectric phase, activation energy was determined and the value is Eτ = 0.68 eV. The present ceramic is promising candidate for high dielectric constant and low loss dielectric ceramic.

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Keyword: ferroelectric, tetragonal tungsten bronze, phase transition, dielectric permittivity, impedance.

Corresponding author : el.choukri@yahoo.fr
1 LMCN, F.S.T.G.University Cadi Ayyad Marrakech, Morocco.
2 LPMC, Université de Picardie, 33, rue Saint-Leu, 80039 Amiens Cédex, France.
3 L2MP, UMR-CNRS 6137, Université de Toulon-Var, BP 132, 83957 La Garde Cédex, France.

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Volume 12, Num 2 article 14

NEW DEFECT PYROCHLORE SOLID SOLUTION IN THE
KBi₂M₅O₁₆ – TlBi₂M₅O₁₆ (M=Nb, Ta) SYSTEMS

A. Chagraoui*, O. Ait Sidi Ahmed And A. Tairi

Synthesis and caraterization of new solids solutions K1-xTlxBi2M5O16 with (0≤x≤1; M=Nb, Ta) defect pyrochlore type.
Two solid solutions K_1-xTl_xBi₂M₅O₁₆ (0≤x≤1; M=Nb, Ta) were prepared using solid state reaction method and characterized by x-ray diffraction and Infrared absorption spectroscopy. All compositions were indexed in the cubic system (space group Fd3m) and showed the defect pyrochlore-type structure like oxides as ABi₂M₅O₁₆ (A=K, Tl; M=Nb, Ta) [1]. The cell parameter of the two defect pyrochlores solid solutions varies linearly with increasing x of compositions from a=10.5701(1) Å to a=10.5343(1) Å for K_1-xTl_xBi₂Nb₅O₁₆ (0≤x≤1) and from a=10.5489(1) Å to a=10.5144(1) Å for K_1-xTl_xBi₂Ta₅O₁₆ (0≤x≤1).
Résumé – Synthèse et caractérisation de nouvelles solutions solides K_1-xTl_xBi₂M₅O₁₆ (0≤x≤1; M=Nb, Ta) de type pyrochlore déficitaire. Deux solutions solides K_1-xTl_xBi₂M₅O₁₆ (0≤x≤1; M=Nb, Ta) ont été préparées à l’état solide et caractérisées par diffraction des rayons X et par spectroscopie d’absorption infrarouge. Toutes les compositions des solutions solides cristallisent dans le système cubique (groupe d’espace Fd3m) et appartiennent à la famille des pyrochlores déficitaires, ABi₂M₅O₁₆ (A=K, Tl; M=Nb, Ta) [1]. Le paramètre de maille des deux solutions solides varie linéairement avec la composition x de a=10.5701(1) Å à a=10.5343(1) Å
pour K_1-xTl_xBi2Nb₅O₁₆ (0≤x≤1) et de a=10.5489(1) Å à a=10.5144(1) Å pour K_1-xTl_xBi₂Ta₅O₁₆ (0≤x≤1).

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Laboratoire de Chimie Analytique et Physico-chimie des Matériaux, Faculté des Sciences Ben M’Sik Casablanca, Université Hassan II-Mohammedia , Morocco.

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Volume 12, Num 2 article 15

Electrical Transport Properties Of Iodine Oxide Phosphate Glasses Issued From The NaI-Li₂O-WO₃-P₂O₅ System

H. Bih¹, L. Bih², B. Manoun², M. Azrour², B. Elouadi³, P. Lazor⁴

This work concerns the investigation of ion transport behaviour of NaI containing lithium tungsten phosphate glasses in order to understand better the role of NaI in the ionic cation transport. Glasses obtained in the system 0.5[x(2NaI)-(1-x)Li2O]-0.5[0.25(WO3)2-0.75P2O5] were investigated. The glass samples have been characterised using powder X-ray diffraction (XRD), thermal analysis, density and impedance spectroscopy. X-ray diffraction and thermal studies have confirmed that these glasses can be formed in the range x = 0 to 1. The mixed alkali glasses have shown higher activation energies and lower conductivities compared to single alkali doped glasses and this has been attributed to a mixed alkali effect.

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Keyword: ion conductivity, glass transition temperature, glasses, tungsten oxide, phosphate and NaI.

1 Département de Chimie, FST-Guéliz, Marrakech, Morocco.
2 Equipe Sciences des matériaux, FST- Errachidia, B.P 509, Boutalamine, Morocco.
3 LEACHIM, Université de La Rochelle, France.
4 Earth Geology Department, Uppsala University, Sweeden.

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Volume 12, Num 2 article 16

Dielectric Properties of new Ferroelectric Lead Potassium Niobate Pb_0.9K_0.2Nb₂O₆

A. Belboukhari¹, D. Mezzane¹ Y. Gagou², M. Elmarssi², I. Luk’yanchuk², A. Zegzouti³, P. Saint-Grégoire⁴

In this paper we report the dielectric properties of ferroelectric compound Pb0.9K0.2Nb2O6 (PKN-0.1) that was elaborated by a standard solid-state reaction technique and characterized by X-ray diffraction,  Raman diffusion and scanning electron microscope  techniques confirming its tetragonal tungsten bronze (TTB) crystallographic structure. The dielectric permittivity and the loss tangent of the sample have been measured in a frequency range 20Hz–1MHz and a temperature range 35–550°C. The ferroelectric-paraelectric phase transition was observed at Tc=518°C witch follow the Curie-Weiss law. AC impedance plots were used as tool to analyse the electrical behaviour of the sample as function of frequency at different temperature. The obtained results indicate the non-Debye type dielectric relaxation.

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Keyword: Ferroelectric, Tetragonal Tungsten Bronze (TTB), Phase transition, lead potassium niobates, impedance spectroscopy.

1 LMCN, F.S.T.G.University Cadi Ayyad Marrakech, Morocco.
2 LPMC, Université de Picardie, 33, rue Saint-Leu, 80039 Amiens Cédex, France.
3 F.S.S. University Cadi Ayyad Marrakech, Morocco.
4 L2MP, UMR-CNRS 6137, Université de Toulon-Var, BP 132, 83957 La Garde Cédex, France.
Address of Author: mezdaoud@yahoo.fr

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Volume 12, Num 2 article 17

Investigation Of Nanoscale Dielectric Polarization And Refractive Indices Of BaTiO₃ Surfaces And Ultrathin Films

H. Chaib^1,*, L. M. Eng², A. Nafidi³, A. Khalal³, A. Tirbiyine⁴, and A. Taoufik⁴

The surface and interface effects on the dielectric polarization and refractive indices of BaTiO₃ single crystals and BaTiO₃ ultrathin films on SrTiO₃ single crystal substrates are investigated theoretically by using a microscopic model based on the orbital approximation in correlation with the dipole-dipole interaction. The spontaneous polarization of BaTiO₃ single crystals is drastically reduced near the c-surface. For BaTiO₃/SrTiO₃ films, the spontaneous polarization is reduced in the film as its thickness decreases. However, an electronic polarization appears within the SrTiO₃ substrate in the neighborhood of the interface. This polarization, which vanishes far away from the interface into the SrTiO3 bulk, is induced by the polarization of the BaTiO₃ film. Furthermore, we find the refractive index either for BaTiO₃ single crystals or for BaTiO₃ films and SrTiO₃ substrates to be strongly reduced for light polarized perpendicular to the surface.

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1 Polydisciplinary Faculty, Ibn Zohr University, P.O. Box 83, 45002 Ouarzazate, Morocco.
2 Institute of Applied Photophysics, University of Technology, D-01062 Dresden, Germany.
3 Condensed Matter Physics Group, Faculty of Sciences, Ibn Zohr University, Agadir, Morocco.
4 Group of High Critical Temperature Superconductor Materials, Faculty of Sciences, Ibn Zohr University, Agadir, Morocco.

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Volume 12, Num 2 article 18

The influence of layer defect in the Ferroelectric films

A. Oubelkacem¹, A. Ainane^1,2,3,* , I. Essaoudi¹; M. Saber^1,2 and F. Dujardin³

Using the modified transverse Ising model, and the effective field theory based on the probability distribution technique, the phase transition temperature, the polarization and susceptibility for ferroelectric thin films with structural defects are studied. It is shown that the defect layers in ferroelectric thin films can induce strong increase or decrease of the critical temperature of ferroelectric phase transition due to different exchange interactions in the defect layers. The obtained results are in qualitative agreement with experimental data for thin ferroelectric film with different thickness.

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1 Faculté des Sciences, Département de Physique, B.P. 11 201, Zitoune, Meknès, Morocco.
(Unité Associée CNRST-URAC).
2 Max-Planck-Institut fûr Physik Complexer Systeme, Nôthnitzer Str. 38 D-01187 Dresden, Germany.
3 Laboratoire de Physique des Milieux Denses (LPMD) Institut de Chimie, Physique et Matériaux (ICPM), 1 Bd. Arago, 57070, Metz, France.

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Volume 12, Num 2 article 19

Composition-temperature phase diagram for Barium-doped lead zirconate ferroelectric ceramics determined by Raman spectroscopy

I. El-Harrad¹ and A. Ridah²

The ceramic (Pb_1-XBa_X)ZrO₃ composition, hereafter abbreviated PBZ-x, is a ceramic solid solution with perovskite structure. The effect on the antiferro-ferro-paraelectric phase transitions sequence caused by Barium substitution in Pb-sublattice is Raman spectroscopically evidenced and discussed. Furthermore, the basic features of the composition-temperature phase diagram of PBZ-x (x ≤0.5) solid solutions were established.

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1 Matériaux Optoélectroniques et Photonique, Labotratoire d’ Optoélectronique et Techniques Energétiques, Faculté des Sciences et Techniques Errachidia, BP 509, Boutalamine 52000, Errachidia, Morocco.
2 Laboratoire de Contrôle et d’Analyse des Matérieux, Faculté des Sciences Ben Msik, BP 7955, Casablanca, Morocco.

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Volume 12, Num 2 article 20

Ising-Like Model For Ferroelectric Phase Transitions In Tetragonal Tungsten Bronze Compounds

E.Taifi^1,2,3, Y. El Amraoui¹, H. Arhchoui¹, D.Mezzane², I. Luk'yanchuk³

The two-component anisotropic Ising-like model was proposed to model the ferroelectric phase transitions in Tetragonal Tungsten Bronze (TTB) compounds. Using the mean-field approach we reconstructed the phase diagram of the TTB system and showed that depending on he relative strength of the interaction parameters there ferroelectric states are possible: (i) the state with y-directed polarization that corresponds to the tetragonal ferroelectric phase in TTB compounds, (ii) the state with x-directed polarization that corresponds to the orthorhombic TTB phase and (iii)  the state with superposition of x- and y- polarization components that can correspond to the not yet discovered mixed phase.

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1 Laboratoire de Physique Statistique et Modélisation des systèmes, département de Physique, Errachidia, Morocco.
2 LMCN, département de Physique, FSTG, UCAM, Marrakech, Morocco.
3 Laboratoire de Physique de la Matière Condensée de l'Université de Picardie Jules Verne", France.

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Volume 12, Num 2 article 21

Preparation And Characterisation Of Zno Thin Films Deposited By SILAR Method

A. Raidou^a, M.Aggour^a, A. Qachaou^a, L. Laanab^b, M. Fahoume^a

Zinc oxide (ZnO) thin films were grown on glass and copper substrates by the Successive Ionic Layer Adsorption and Reaction (SILAR) technique.
ZnO films are obtained by successive immersion of a substrate in an aqueous solution containing: ZnSO4 with different molarities, 6ml/100ml 13.15 M aqueous ammonia solution and in deionised water heated at different temperatures.
We studied the structural, morphological and optical properties with the deposition parameters (pH, bath temperature, number of cycles…)
The structural, morphological surface and optical properties of the films have been studied by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-VIS-spectrophotometer. Effects of experimental parameters and heat treatment on the structural and optical properties were discussed. The X-ray diffraction analysis shows that the films are polycrystalline with zincite hexagonal structure with the preferential orientation of (002) plan.
The study of surface morphology reveals that deposited ZnO films take many shapes: nanorods, nanoprisms, flower-like, needles, spindles and hexagonal structures. Obtained ZnO films exhibit a high transmittance of 90% in visible band, and optical band gap of 3.27 eV.

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a L.P.M.C., Faculté des Sciences, Université Ibn Tofail, BP.133-14000 Kénitra, Morocco.
b L.C.S., Faculté des Sciences, université Mohammed V, BP.1014 Rabat, Morocco.

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Volume 12, Num 2 article 22

Characterization Of Mortars With Ultrasonic Transducer

H.Lotfi^1,*, B.Faiz¹, A.Moudden^1,2, D.Izbaim¹, A.Menou³, G.Maze⁴

The durability of mortar structures is affected by chemical and mechanical factors, such as abrasion, temperature variation..., the Degradation of mortar structures located under flowing water in their structure or high humidity atmospheres. In this study we presented a method for ultrasonic non-destructive characterization in mortar to follow the evolution of the signals back scattered by mortar structures for different size of sand, Samples were manufactured using same water/cement ration (w/c) 0.65, and cement/sand ration (c/s) 0.5. The processing of the ultrasound wave has been chosen to follow the hardening of mortar and to understand the mechanisms driving to the degradation of mortar in relation with microstructure.

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1 Laboratoire Métrologie et Traitement de l’Information Faculté des Sciences B.P. 8106 Agadir Morocco.
Phone: +212667099598; e-mail: lotfi.hicham@yahoo.fr
2 Ecole Supérieur de Technologie  Agadir Morocco.
3 ONDA Casablanca Morocco.
4 Laboratoire Ondes et Milieux Complexe Université Le Havre France.

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Volume 12, Num 2 article 23

New Study Of Electrical Conductivity In Ni-Doped Non -Stoichiometric Lithium Tantalite

A. Khalil¹, N. Masaif^1,2, A. Jennane^1,2 and K. Maaider¹

Electrical conductivity in Ni-doped nonstoichiometric lithium tantalite was described by a new theoretical approach. From the experience, we have proposed the new vacancy models which are able to describe substitutional mechanism in Ni-doped lithium tantalite. A combinaison of phase transition theory and generalised vacancy models allows us to establish a new expression of electrical conductivity which takes into account the defect structure of Ni-doped lithium tantalate. Calculations of the conductivity in Ni-doped nonstoichiometric lithium tantalate reveal good correspondence with experimental results.

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1 Laboratoite Rayonnement & Matiere–Equipe de Recherche Physique de la Matiere et Modelisation Faculté des Sciences et Techniques BP 577 Settat, Morocco.
2 Université Hassan 1er, Ecole Nationale des Sciences Appliquées BP 77 Khouribga, Morocco.

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Volume 12, Num 2 article 24

Some Theoretical Results of Ferroelectric Transition In The Doped Crystal LiMO₃ (M= Nb, Ta)

A. Khalil¹, N. Masaif^1,2, A. Jennane^1,2 and K. Maaider¹

This work behaves like an extension of the Safaryan theory. A new analytical description has been proposed based on the vibrations of crystal planes. LiMO₃ is formed by a succession of the plans in the following sequence: Li, M, O₃, etc.  In the N doped LiMO₃ crystal, we supposed that the LiNMO₃ system is formed by a succession of the plans of the sequence: Li, N, M, O, ect. These four crystalline plans vibrate in the direction of trigonal c-axis where each plan consists the ions Li+, N^x+, M⁵⁺ or O^2-. The dynamic solution of the vibrations of these planes shows that one of two optical branches describes the soft mode at the ferroelectric transition in LiNMO₃. From dispersion equation, we have show the bond between the soft mode frequency, the Curie temperature, the charges, the masses of ions and the distance between these ions. The substitution mechanism of the doped compositions N in LiMO₃ crystal is discussed. So, the mechanism of phase transition due to thermal expansion of crystal is described.

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1 Laboratoite Rayonnement & Matiere–Equipe de Recherche Physique de la Matiere et Modelisation Faculté des Sciences et Techniques BP 577 Settat Morocco.
2 Université Hassan 1er, Ecole Nationale des Sciences Appliquées BP 77 Khouribga Morocco.

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Volume 12, Num 2 article 25

An Approach To The Defect Structure Analysis Of Niobate And Tantalate Lithium Ilmenite Type Structure

K. Maaider¹, A. Jennane^1,2, N. Masaif^1,2 and A. Khalil¹

We present in this work a comparative study between normal LiNbO₃ (LiTaO₃) and ilmenite structural LiNbO₃ (LiTaO₃). Namely, the normal cation stacking sequence is replaced by ilmenite ordering …Nb (Ta) Li vacancy Li Nb (Ta) vacancy Nb (Ta) Li vacancy Li Nb (Ta) vacancy… From Safaryan’s approach which combines a ferroelectric phase transition theory and vacancy models we calculated the Curie temperature in ilmenite _LiNbO3 (LiTaO₃). Comparatively, we showed that the ilmenite structural LiNbO₃ (LiTaO₃) is in an excellent agreement with experiment result than normal LiNbO₃ (LiTaO₃).

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1 Matériaux Optoélectroniques et Photonique, Labotratoire d’ Optoélectronique et Techniques Energétiques, Faculté des Sciences et Techniques Errachidia, BP 509, Boutalamine 52000, Errachidia, Morocco.
2 Laboratoire de Contrôle et d’Analyse des Matérieux, Faculté des Sciences Ben Msik, BP 7955, Casablanca, Morocco.

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Volume 12, Num 2 article 26

New Approach To Study The Influence Of The Defect Structure On The Refractive Indices Of Mg-Doped Lithium Niobate

K. Maaider¹, A. Jennane^1,2, N. Masaif^1,2 and A. Khalil¹

We proposed a new approach to calculate the refractive indices of Mg-doped lithium niobate using generalized vacancy models combined with a ferroelectric phase transition theory. We have obtained a generalised Sellmeier equation which takes into account the defect structure and Mg-doped lithium niobate. A comparison between the calculated values from this approach and the experimental data of the temperature and refractive indices is detailed.

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1 Laboratoite Rayonnement & Matiere–Equipe de Recherche Physique de la Matiere et Modelisation Faculté des Sciences et Techniques BP 577 Settat Morocco.
2 Université Hassan 1er, Ecole Nationale des Sciences Appliquées BP 77 Khouribga Morocco.

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Volume 12, Num 2 article 27

Nonresonant Raman Spectrum Of Boron Doped Single Walled Carbon Nanotubes

A. ElBiyaali, B. Fakrach, M. Bentaleb,H. Chadli and A. Rahmani

In the present work, We use a force constant model to study the vibrationnel modes of boron doped single walled carbon nanotubes. This model is used to calculate the nonresonant Raman spectra of these nanomaterials in the framework of bond-polarisation theory by using either direct diagonalisation of the dynamical matrix or the spectral moments method. The effect of substitution of carbon by boron atoms shows that the higher Raman frequency region is dominated by a broad bond whereas the lower one is characterized by a shift of radial bonds.

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Laboratoire de physique des matériaux et modélisation des systèmes,Université MY Ismail, Faculté des sciences, BP 11201, Zitoune, 50000 Meknès, Morocco.

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Volume 12, Num 2 article 28

Measurement Of The Nonlinear Ultrasonic Parameter In Aqueous Solutions

H Jakjoud^1,2, A Chitnalah¹, N Aouzale¹, D. D. Caviglia²

This paper deals with the measurement of the nonlinear ultrasound coefficient in aqueous solutions. Our aim is to show the possibility of using this parameter in ultrasound characterization of these solutions with the possibility of extending this technique to other complex media. The experimental determination of nonlinearity parameter is based on the quasi-linear approximation that allows us to derive an analytical expression of the second harmonic amplitude that takes into account the diffraction and the absorption effects. The experimental set up is composed of a piezoelectric disc transmitting at the fundamental frequency 2.2 MHz. The second harmonic is detected using a ring surrounding the disc and functioning at 4.4 MHz. The disc and the ring are both mounted on the same composed device and are both located in the same transversal plan to the propagation axis. The transmitted wave propagates through the sample and is detected by the receiver An appropriate signal processing permits the determination of the nonlinear parameter. The experimental results are promising and show a close correlation between the nonlinearity parameter, and the nature and the concentration of the compounds in the aqueous solutions studied.

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1 Laboratoire des Systèmes Electriques et Télécommunications L.S.E.T. Université CADI AYYAD FST BP 549, 40000 Gueliz Marrakech,  Morocco.
2 Departement de l’Ingénierie Biologique et Electronique (DIBE)Université de Gènes Italy.
hicham.jakjoud@gmail.com

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Volume 12, Num 2 article 29

Experimental And Theoretical Study Of The Substitution Mechanism In The W6+: Litao3 Correlated With The Ferroelectric Properties

M. Tahiri¹, N. Masaif^1,3, E. M. Lotfi² and A. Jennane^1,3

The purpose of the present work is to report the latest results of our experimental and theoretical non-stoichiometry investigations of solid solutions isolated close to LiTaO₃ inside the ternary system Li₂O-Ta₂O₅-(WO₃)₂ correlated with the ferroelectrics transitions. Dielectric measurements performed on ceramic samples have shown that ferro-paraelectric temperatures transitions T_C varied along the solids solutions, as the stoichiometry deviates from LiTaO₃. A Safaryan’s theory of ferroelectric transition and the various vacancy models in this work reproduce well the experimental results by explaining the substitution nature of Tungsten hexavalent (W⁶⁺) in LiTaO₃.

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1 Laboratoire Rayonnement & Matière–Equipe de Recherche Physique de la Matière et Modélisation, Faculté des Sciences et Techniques, BP 577 Settat Morocco.
2 Département Génie Mécanique, ENSET, B.P.: 6207, Rabat Instituts, Université Mohammed V- Souissi - Rabat, Morocco.
3 Université Hassan 1er, Ecole Nationale des Sciences Appliquées, BP 77 Khouribga, Morocco.

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Volume 12, Num 2 article 30

An Approach To The Defect Structure Analysis Of Lithium Niobate Ilmenite Type Structure

M. Tahiri¹, N. Masaif^1,2 and A. Jennane^1,2

We present in this work a comparative study between the normal and the ilmenite structural of LiNbO₃. Namely, the normal cation stacking sequence is replaced by the ilmenite ordering: …Nb Li vacancy Li Nb vacancy Nb Li vacancy Li Nb vacancy…. . From Safaryan’s approach which combines a ferroelectric phase transition theory and vacancy models we allows to calculate the Curie temperature in ilmenite LiNbO₃. Comparatively, we showed that the ilmenite structural LiNbO₃ is in an excellent agreement with experiment result than the normal LiNbO₃

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1 Laboratoire Rayonnement & Matière –Equipe de Recherche Physique de la Matière et Modélisation , Département de Physique Faculté des Sciences et Techniques,
BP 577 Settat Morocco.
2 Université Hassan 1er, Ecole Nationale des sciences appliquées BP 77 Khouribga Morocco.

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Volume 12, Num 2 article 31

Synthesis And Characterization Of Two New Antimony Phosphates Co_0,5alsb(PO₄)₃ And Mg_0,5fesb(PO₄)₃

H. Sinouh^(a), A. EL Bouari^(a)*, S. Benmokhtar^(a), L. Bih^(b) A. Faik^(c)

Two new antimony phosphates Co_0,5AlSb(PO₄)₃ and Mg_0,5FeSb(PO₄)₃ were synthesized for the first time by the solid-state reaction method. Their crystal structures have been refined at room temperature from X-ray powder diffraction data using Rietveld method. Co_0,5AlSb(PO₄)₃ crystallizes in the space group R-3c (N°167) (a_h = 8.23±0.01Ǻ, c_h = 21.94±0.02Ǻ). Mg_0,5FeSb(PO₄)₃ crystallizes in the monoclinic space group P_21/n (N°14) (a_m =11.54 Ǻ, b_m = 8.83± 0.02 Ǻ, c_m = 8.39± 0.01 Ǻ, β = 96.67°± 0.09). Raman and infrared spectra were recorded and assignments of the stretching and bending vibrations of the PO₄^3- tetrahedra were made. The number of the peaks observed is in good agreement with that predicted by the factor group analysis of the R-3c et P_21/n space group respectively. Vibrational spectral studies of two antimony phosphates were collected in-situ at room-pressure and at elevated temperatures, up to 430 oC. At elevated temperatures in air, Mg_0,5FeSb(PO₄)₃ seems to be stable, but
Co_0,5AlSb(PO₄)₃ show a transition at 380°C and decomposes at 930°C. This result has been confirmed by differential scanning calorimetric study (DSC).

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(a) Laboratoire de Chimie des Matériaux Solides, Faculté des Sciences Ben M’Sik Casablanca, Morocco.
(b) Laboratoire de Physico-Chimie des Matériaux – LPCM, Faculté des Sciences et Techniques Errachidia, Morocco.
(c) CNRS-CEMHTI, 1D Av. de la Recherche Scientifique, 45071 Orleans Cedex 2, France

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Volume 12, Num 2 article 32

Modeling Of Residual Stresses In Thin Films Of Y₂O₃ Deposited On Si Substrate, SrTiO₃ and M_gO

Abdellah Boualam*, Brahim Boubeker*,  Abdellah Zamma*, Fabien Paumier**

The study concerns the analysis of residual stress in thin films obtained by IBAD (Ion Beam Assisted Deposition). Only the thermal stress in the film can be calculated and it has no other information on other types of constraints. Kamminga and Al have proposed a model in which they describe the stress state as a combination of a hydrostatic stress caused by the introduction of particles into the holes of the matrix of the film and a fixing constraint to keep the lateral dimensions of the film identical to those of the substrate. We apply this model to determine the stresses in the films of yttrium deposited by IBS of Si substrates, SrTiO₃ and MgO. New phosphonated cross-linked materials were synthesized from telomers obtained by reaction between 10-undecenol and dialkyl hydrogenphosphonates. Telomers were then converted to materials resins by methacrylation reactions. Finally, photopolymerization of the different materials synthesized was achieved and influence of the nature of the phosphonate group (diester, monoacid and diacid) was also evaluated.

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*Laboratoire de Caractérisation des Matériaux, Faculté des Sciences Ben M’Sik Av. Driss Harti, Sidi Othman, Casablanca Morocco.
**Université de Poitiers, UFR Sciences, S.P.2M.I, Laboratoire de Métallurgie Physique, URA 131 du CNRS, Bd 3, Téléport 2, BP. 179, 86960 Futuroscope cedex, France.

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Volume 12, Num 2 article 33

Synthesis Characterization And Photopolymerization Of Novel Phosphonated Materials

O. Senhaji1^1,2*, E. Derwich³, M.K. Skalli³, A.H.Benali⁴, M. Achchoubi¹, J.J. Robin², M. Filali-Baba³, R. Taouil⁵

New phosphonated cross-linked materials were synthesized from telomers obtained by reaction between 10-undecenol and dialkyl hydrogenphosphonates. Telomers were then converted to materials resins by methacrylation reactions. Finally, photopolymerization of the different materials synthesized was achieved and influence of the nature of the phosphonate group (diester, monoacid and diacid) was also evaluated.

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1 Laboratoire de Chimie Physique Appliquée (LCPA), Faculté des Sciences et Techniques.Université Moulay Ismaïl, Errachidia. Morocco. E-mail : ossenhaji@yahoo.fr
2 Laboratoire de Chimie Macromoléculaire (LCM), UMR 5076 – Hétérochimie Moléculaire et Macromoléculaire, USTL, ENSCM, 8, rue de l’Ecole Normale,
   34 296 Montpellier cedex 5. France.
3 Université Sidi Mohammed Ben Abdellah, Fès, Morocco.
4 Faculté des Sciences - Oujda – Morocco.
5 Physique Faculté des Sciences et Techniques, Errachidia. Morocco.

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Volume 12, Num 2 article 34

Influence Of The Ti/Al Substitution On Ba/La Cationic Order In The Ba_6-x-yLa_8+2/3x+yTi_18-yAl_yO₅₄ Solid Solution

Mohamed ABOU-SALAMA^1,*, Karim CHOURTI¹, Pascal MARCHET²

The study of the Ba/La order in the Ba_6-x-yLa_8+2/3x+yTi_18-y Al_yO₅₄ solid-solution was performed by X-ray diffraction on powders and single-crystals. The crystal structure of these phases belongs to the tetragonal tungsten bronze type, build on the basis of (3x3) TiO₆ octahedron more than (2X2) (space group Pnma, a≈22.4Å, b≈7.7Å, c≈12.2Å). Two structural models were built, corresponding to two different orders within the structure. The model I, of formula [Ba₄] _A2  [Ba_2-z La_{2x/3+y+q  q’} ]_A1'[La_{8-q' q}] A1Ti18-y AlyO54, corresponds to a model associated to infinite perovskite rows parallels to Oy axis, build on the basis of (3X3) TiO6 octahedron. The model II, with formula [Ba_{6-z z-2}] _A2 [La_{8+2x/3+y 2-(2x/3)-y}] _A1’A1Ti_18-yAl_yO₅₄, can be described on the basis of three perovskite octahedron layers parallels to xOz plane.

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1 Département de chimie, Faculté Pluridisciplinaire de Nador, B.P:300 Selouane 62700 Nador, Morocco.
2 Laboratoire de science des procédés céramiques et de traitements de surface UMR 6638 CNRS, Université de Limoges, 123 Avenue Albert thomas 87060 Limoges cedex, France.
*Corresponding author, e-mail : m.abousalama@hotmail.com ( Mohamed ABOU-SALAMA).