M. Dammak

Electrical properties of ferroelectric addition compound K2SeO4.Te(OH)6

Abstract Single crystals of K 2 SeO 4 .Te(OH) 6 , (KTSe) were obtained by slow evaporation at 300 K. The differential scanning calorimetry diagram showed three anomalies at 433, 480 and 495 K, respectively. The dielectric constant evolution as a function of frequency and temperature revealed the first two anomalies. The peak at 433 K was attributed to the ferroelectric–paraelectric phase transition and the second one to the superionic phase transition. X-ray powder diffraction data confirmed that the third anomaly at 495 K characterizes the decomposition before melting of the material.

Biological properties and biodegradation studies of chitosan biofilms plasticized with PEG and glycerol

Chitosan biofilms, prepared by casting method at various percentage of plasticizer (PEG and glycerol), were evaluated for their biological, structural and thermal properties. The addition of PEG at 30% (w/w) and glycerol at 10% (w/w) to chitosan has increased the antioxidant activity of biofilm with the percentages of 22 and 26%, respectively. The increase of ferric reducing power was noted for the mixtures of chitosan-PEG (70-30) and chitosan-GLY (75-25). Additionally, the antibacterial properties of several biofilms were tested against E. coli and S. aureus. Biofilms with 70-30 and 90-10 blends ratio of chitosan-PEG and chitosan-GLY showed the best inhibitory effect against E. coli and S. aureus with 12 and 27%, respectively. All biofilms were degraded in compost in liquid and the addition of plasticizer PEG to chitosan increased his biodegradability with a value of BOD5 about 2.33 O2/mg CO. FT-IR spectra showed that the addition of plasticizer promoted the interactions through hydrogen bonding as reflected on the shifting of main peaks but there is no effect on biodegradation.

Spectra and energy levels of Yb3+ in AlN

We report on the crystal-field energy levels calculation of Yb3+ ions in an AlN host using crystal-field theory. Cathodoluminescence spectra of AlN grown by molecular beam epitaxy on Si (0001) substrate and doped by implantation with ytterbium (Yb) ions were critically examined assuming that Yb3+ ions are involved in different sites. The comparison between the emission spectra of Yb3+ ions in the GaN and AlN indicates the presence of some similarities between the lattice locations of Yb3+ ions in these hosts. We demonstrate that assuming the existence of a substitutional YbAl(Ga) site and a VN-Yb complex defect in AlN (GaN) lattice, a good agreement between the measured and calculated energy values of Yb3+ ion transition lines can be obtained. Furthermore, we have investigated the Zeeman g∥ and g⊥ parameters for the Yb3+ ion in an Al substitutional site as well as in the VN-Yb complex using the perturbation theory.

Non-isothermal model-free predictions

Suitable thermal treatment of metal organic precursors is a key process to obtain oxide films. To this purpose, non-isothermal model-free predictions are specially suited. In this article we will explore the ability of these methods to provide an accurate prediction of the evolution of the decomposition of yttrium trifluoroacetate, a precursor used in the synthesis of YBaCuO superconducting thin-films. A good agreement has been obtained between the predicted and the measured reaction courses.

Conductivity study of a new protonic conductor Rb1.12(NH4)0.88SO4·Te(OH)6

Abstract Single crystals of Rb 1.12 (NH 4 ) 0.88 SO 4 ·Te(OH) 6 were obtained by slow evaporation at 300 K. Differential scanning calorimetry showed an anomaly at 418 K, two shoulders at 482 and 510 K and one strong peak at 517 K. X-ray diffraction shows that the first DSC peak at 418 K passes the material from paraelectric to ferroelectric phase. A conductivity study shows that the shoulder at 482 (which masks a second one at about 458 K) can be attributed to a superprotonic phase transition. Dielectric constant and dissipation factor evolutions indicate that the peak at 458 K is probably due to a ferroelectric–paraelectric phase transition. The strong peak at 517 K was attributed to the decomposition of the salt.

Structure, thermal behavior and characterization of a new hybrid iron fluoride FeF4(2,2′-bipyridine)(H2O)2

New crystal of FeF4(2,2′-bipyridine)(H2O)2 was prepared by hydrothermal synthesis. Crystalline structure determination is performed from single crystal X-ray diffraction data. The unit cell is monoclinic space group P21/n, with cell parameters a=0.9046(5) nm, b=0.7502(5) nm, c=1.9539(5) nm, β=93.307(5)°, V=1.3238(12) nm3 and Z=4. The structure of FeF4(2,2′-bipyridine)(H2O)2 is built up from FeF4N2 octahedra coordinated by two nitrogen atoms of the 2,2′-bipyridine molecules, and four fluorine atoms as well as uncoordinated H2O molecules. Thermal analysis of the title compound showed that the decomposition introduced four steps. IR spectra confirmed the presence of 2,2′-bipyridine molecules. The optical absorption was measured at the corresponding λmax using UV-Vis diffuse reflectance spectrum.

Spectroscopic properties of Eu3+ doped RbLaP4O12 powders.

Monophasic RbLaP4O12 possessing monoclinic symmetry with varied Eu(3+) concentrations was synthesized by flux method. The obtained cyclotetraphosphate exhibits very small crystals and the dopant Eu(3+) ions were successfully incorporated into the sites of La(3+) ions of the host lattice. These compounds were characterized by infrared and Raman spectroscopy, X-ray diffraction (XRD) and luminescence spectroscopy. The spectroscopy properties confirm the potentiality of present RbLaP4O12 doped with Eu(3+) ions as luminophore host materials to produce an intense red luminescence at 616 nm corresponding to (5)D0→(7)F2 emission level and have significant importance in the development of emission optical systems.

Synthesis, structural study and phase transitions characterization by thermal analysis and vibrational spectroscopy of an ammonium rubidium arsenate tellurate

The Rb2.42(NH4)0.58(HAsO4)(H2AsO4)·Te(OH)6 crystals(denoted by RbNAsTe) crystallize in the monoc-linic system, space group P21/n with the following parameters: a=1.3059(5) nm, b=0.6755(3) nm, c=1.6675(6) nm, β=94.126(4)°, Z=4 and V=1.46733(10) nm3. Thermal analyses(DSC, DTA and TG) confirm the presence of the phase transition and the temperature of the decomposition. The vibrational spectroscopy study at room temperature show the presence and the independence of anionic groups, cationic groups, and give more importance to the hydrogen bonds. Raman spectra were recorded in the temperature range of 298―503 K. The temperature dependence of the Raman line shift, intensity reduction and the half width detects the phase transitions and confirms their nature. So, the phase transition at 453 K corresponds to the superprotonic-ionic conduction phase transition, and those at 483 and 491 K correspond to the decomposition of our material.

Redetermination of the crystal structure of β-zinc molybdate from single-crystal X-ray diffraction data

The crystal structure of the β-polymorph of ZnMoO4 was re-determined on the basis of single-crystal X-ray diffraction data. In comparison with previous powder X-ray diffraction studies [Katikaneani & Arunachalam (2005 ▸). Eur. J. Inorg. Chem. pp. 3080–3087; Cavalcante et al. (2013 ▸). Polyhedron, 54, 13–25], all atoms were refined with anisotropic displacement parameters, leading to a higher precision with respect to bond lengths and angles. β-ZnMoO4 adopts the wolframite structure type and is composed of distorted ZnO6 and MoO6 octahedra, both with point group symmetry 2. The distortion of the octahedra is reflected by variation of bond lengths and angles from 2.002 (3)–2.274 (4) Å, 80.63 (11)–108.8 (2)° for equatorial and 158.4 (2)– 162.81 (14)° for axial angles (ZnO6), and of 1.769 (3)–2.171 (3) Å, 73.39 (16)–104.7 (2), 150.8 (2)–164.89 (15)° (MoO6), respectively. In the crystal structure, the same type of MO6 octahedra share edges to built up zigzag chains extending parallel to [001]. The two types of chains are condensed by common vertices into a framework structure. The crystal structure can alternatively be described as derived from a distorted hexagonally closed packed arrangement of the O atoms, with Zn and Mo in half of the octahedral voids.

Theoretical analysis and intensity calculation for the f → d absorption spectrum of Ce3+ in YAl3(BO3)4 crystal

Emission, absorption, and excitation spectra of 4f → 5d transitions of Ce3+ ions in yttrium aluminum borate (YAB) crystal are reviewed and successfully reproduced by theoretical investigations. The Ce3+ energy level diagram has been compiled after a careful analysis of the optical spectra. Theoretical calculations based on free ion and crystal field Hamiltonians are used to interpret the observed transitions. The 4f and 5d crystal field parameter permits determination of the engine states of Ce3+ ion in YAB and then calculating the absorption line intensities as well as the effective section and the decay times.