Synthesis and characterizations of Ho2O3 modified SrBi2Nb2O9 ceramics

SrBi_2-xHo_xNb₂O₉ (0?≤?x?≤?0.5) ceramics were prepared through the conventional solid state route. The materials have been characterized by XRD, FTIR and SEM. All compounds were pure and well crystallized. In FTIR spectroscopy, the spectral patterns of the crystal structures of these polyphases are unique and smoothly different from each other. The grains were prone to become spherical with increasing x. Dielectric and electrical properties of these materials as a function of temperature at different frequencies have been carried out. The dielectric constant and dielectric loss were found to decrease with an increase of the holmium concentration at room temperature. Reaching up to x?=?0.4 and x?=?0.5, the diffusivity increases, leading to the occurrence of relaxor behavior. 20–30 at.% Ho doping on the Bi-site can fill up the oxygen vacancies and decrease the AC conductivity. However, at higher doping levels greater than 40% holmium oxide, the AC conductivity is found to increase.     

Synthesis,structural and dielectric properties of SrBi<Subscript>2 – <Emphasis Type="Italic">x</Emphasis></Subscript>Sm<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript>

The SrBi_{2 – x} Sm _x Nb₂O₉ (x = 0, 0.4, 0.5) structure were synthesized by a conventional solid-state method. The X-ray diffraction shows an orthorhombic at room temperature. Dielectric constant, loss tangent and Ac conductivity of Sm-doped SrBi₂Nb₂O₉ were carried out, as well. A higher concentration of samarium (x = 0.4 and 0.5) doping leads to a significant reduction in dielectric constant and in Curie temperature. Rather relaxor type of behaviour took place.     

Deacetylation Regioselective De Glycals

ABSTRACT

Hydrazine acetate is shown to effect selective deacetylation on peracetylated glycals like D-xylal, D-glucal, D-galactal and L-rhamnal. It is demonstrated that the observed selectivity on the -4 position cannot be explained by acetyl migration during the reaction.     

Polymorphism of new rubidium magnesium monophosphate

Novel phase RbMgPO₄, synthesized by solid state reaction, sustains phase transitions at 169 and 184 °C. The medium (β)- and high- (γ) temperature forms (orthorhombic, respectively Pna2₁ and Pnma, Z=4) are typical stuffed tridymites but the ambient form (α) exhibits an unusual three-fold Pna2₁ superstructure that results from the change of coordination of one third of the Mg atoms. Cell parameters are as follows: for α: a=26.535(1) Å, b=9.2926(3) Å, c=5.3368(2) Å; for β: a=8.7938(3) Å, b=9.3698(3) Å, c=5.3956(1) Å; for γ: a=8.7907(3) Å, b=5.4059(1) Å, c=9.3949(3) Å.     

Synthesis and single crystal X‐ray structure of the tetragonal tungsten bronze Pb0.91K1.72Li1.46Nb5O15

Crystals of Pb_0.91K_1.72Li_1.46Nb₅O₁₅, belonging to tetragonal tungsten bronze materials, were grown by the slow cooling technique, and characterized by means of single crystal X‐ray diffraction: the structure was solved in the P4bm tetragonal space group, with the following unit cell parameters: a = 12.548(5), c = 4.042(5) Å, V = 636.4(9) ų. The three‐dimensional framework can be described as a layered structure down crystallographic axis c, with arrays of NbO₆ octahedra, whose corner sharing makes up the formation of tunnels filled up by Li, Pb and K displaying complex cation‐oxygen coordinations. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Study of new rare earth family Pb1.6K1.2R0.2Nb5O15 (R=La, Nd, Sm, Eu and Gd) of tetragonal tungsten bronze-type ferroelectrics

A new ferroelectric rare earth family Pb_1.6K_1.2R_0.2Nb₅O₁₅ with R=La, Nd, Sm, Eu and Gd (PKRN) of tetragonal tungsten bronze type ferroelectrics was synthesized. The ferroelectric transition with nonuniform distribution of critical temperature over a ceramic sample was found from dielectric measurements. According to X-ray diffraction measurements, the ferroelectric phase has an orthorhombic symmetry. The transition temperature was shown to decrease weakly with increasing radius of the rare earth ion R.     

Catalytic behaviors of ruthenium dioxide films deposited on ferroelectrics substrates, by spin coating process

Catalytic ruthenium dioxide films were deposited by spin-coating process on ferroelectric films mainly constituted of SrBi₂Ta₂O₉ (SBT) and Ba₂NaNb₅O₁₅ (BNN) phases. After thermal treatment under air, these ferroelectric-catalytic systems were characterized by X-ray diffraction and scanning electron microscopy (SEM). SEM images showed that RuO₂ film morphology depended on substrate nature. A study of CH₄ conversion into CO₂ and H₂O was carried out using these catalytic-ferroelectric multilayers: the conversion was analyzed from Fourier transform infrared (FTIR) spectroscopy, at various temperatures. Improved catalytic properties were observed for RuO₂ films deposited on BNN oxide layer.     

New insight in the structure–luminescence relationships of Ca9Eu(PO4)7

The double phosphate Ca₉Eu(PO₄)₇, obtained by solid state reaction, was found to be isotypic with Ca₃(PO₄)₂, with space group R3c and unit cell parameters a=10.4546(1) Å, c=37.4050(3) Å, V=3540.67(9) Å³, Z=6. The structure parameters refined using the Rietveld method showed that europium shares positions M1, M2 and M3 with calcium, contradicting previously published Mössbauer results. Low temperature luminescence under selective excitation of Eu³⁺ in Ca₉Y_1−xEu_x(PO₄)₇ and in Ca₉Eu(PO₄)₇ samples was studied, confirming the Eu³⁺ distribution into these sites. At 10 K, ⁵D₀→⁷F₀ emission lines of Eu³⁺ were observed at 578.5, 579.5, 580.1 nm for the M3, M1 and M2 sites, respectively. High temperature X-ray powder diffraction evidenced a second-order phase transition around 573 °C.