Search results for "ionic"

Electric properties of KTiOPO4and NaTiOPO4from temperature-dependent X-ray diffraction

1999

Single crystals of KTiOPO4(KTP) and NaTiOPO4(NaTP) show pronounced pyroelectric behaviour. In order to determine the origin of this property on an atomic scale, X-ray diffraction measurements have been carried out at several temperatures between 100 and 600 K. Modelling of the electron density and the evolution of the structure as a function of temperature has enabled the determination of values for the spontaneous polarization of the compounds and the pyroelectric coefficient of KTP, principally due to the alkaline-ion displacements with a value of 2.0 nC cm−2 K−1. Structure modifications, compared with NaTiOPO4, and the calculation of the electrostatic potential explain the anisotropic be…

Order-disorder evolution in solid solutions of the NLO material KTiOPO : K Rb TiOPO and K Rb TiOPO in the temperature range 293-973 K

2000

K0.88Rb0.12TiOPO4 and K0.465Rb0.535TiOPO4 solid solutions of the potassium titanyl phosphate (KTiOPO4, space group Pna21) family, are described at 293, 473, 673, 873 and at 973 K. Their high resolution structures are obtained by using accurate single-crystal X-ray diffraction techniques at high resolution, (sin A-1. Large anharmonic motion of alkaline ions increasing with temperature allows the evolution of the rubidium and potassium ions repartition in the two alkaline sites versus temperature. To describe this motion inducing ionic conductivity phenomenon and to determine accurately the order-disorder evolution, two alkaline site refinement models are developed and discussed. A thermodyna…

Time-resolved X-ray powder diffraction on a three-way catalyst at the GILDA beamline

2003

Time-resolved X-ray diffraction experiments carried out at the beamline BM08-GILDA of ESRF allowed a study of the structural modifications taking place in a Pt/ceria-zirconia catalyst while the CO oxidation reaction was in progress. The capillary tube in which the sample is stored acts effectively as a chemical microreactor that ensures homogeneity of the sample treatments and minimization of diffusion effects. During the flowing of the reactant CO/He mixture, the investigated catalyst undergoes a fast Ce(IV)-Ce(III) partial reduction that involves the release of one O atom for every two reduced Ce cations. Because Ce(III) has a larger ionic radius than Ce(IV), the structural modification p…

Low-pressure ferroelastic phase transition in rutile-type AX2 minerals: cassiterite (SnO2), pyrolusite (MnO2) and sellaite (MgF2)

2019

The structural behaviour of cassiterite (SnO2), pyrolusite (MnO2) and sellaite (MgF2), i.e. AX2-minerals, has been investigated at room temperature by in situ high-pressure single-crystal diffraction, up to 14 GPa, using a diamond anvil cell. Such minerals undergo a ferroelastic phase transition, from rutile-like structure (SG: P42/mnm) to CaCl2-like structure (SG: Pnnm), at ≈ 10.25, 4.05 and 4.80 GPa, respectively. The structural evolution under pressure has been described by the trends of some structure parameters that are other than zero in the region of the low-symmetry phase’s stability. In particular, three tilting-angles (ω, ω′, ABS) and the metric distortion of the cation-centred oc…

Heterovalent ion replacement in bi7Ti4NbO21: Some new compounds and phase transitions

1996

Abstract Simultaneous heterovalent substitutions at two cationic sites of the bismuth mixed-layered compound Bi7Ti4NbO21 have been made. Two new compounds: Bi2Pb⅓Ti(4/3)Mo⅓O7 and Bi(4/3)PbTiMo⅔O7, were obtained and identified by X-ray diffraction analysis. A model of possible mixed layer structure is discussed. Ferroelectric phase transitions at 510°C and 550°C have been studied by dielectric measurements.

Liquid Structure of Trihexyltetradecylphosphonium Chloride at Ambient Temperature: An X-ray Scattering and Simulation Study

2009

We report on an experimental and simulation study done on a representative room temperature ionic liquid, namely tetradecyltrihexylphosphonium chloride, at ambient conditions. The study was conducted using small and wide angle X-ray scattering and molecular dynamics simulations. Both approaches converge in indicating that this material is characterized by the existence of strong P-Cl interactions (with characteristic distances between 3.5 and 5.0 Å) and by the occurrence of nanoscale segregation, despite the symmetric nature of the cation and similarly to other room temperature ionic liquids. A good agreement is found between the structure factor and pair correlation functions obtained from…

The Significance of Ionic Bonding in Sulfur Dioxide: Bond Orders from X-ray Diffraction Data

2012

A novel refinement technique for X‐ray diffraction data has been employed to derive S-O bond orders in sulfur dioxide experimentally. The results show that ionic S-O bonding dominates over hypervalency.

X-ray scattering studies of fatty acid films on water and on Cdcl2 solutions

1991

X-ray diffraction methods for Langmuir films on the surface of water are briefly presented, together with recent results for docosanoic acid monolayers on pure water and for eicosanoic acid monolayers on an ionic subphase.

Functionalized Diatonic Ionic Liquids Applied to the Study of Michael Addition

The self-association equilibria of doxorubicin at high concentration and ionic strength characterized by fluorescence spectroscopy and molecular dyna…

2019

Abstract The self-association equilibria of doxorubicin hydrochloride (DX), at high drug and NaCl concentrations, are studied by temperature scan fluorescence spectroscopy, with the support of molecular dynamics (MD) calculations. Even though all anthracyclines show dimerization equilibria, DX only can further associate into long polymeric chains according to DXmon ⇄ DXdim ⇄ DXpol. This is reflected not only in the mechanical properties of DXpol solutions (behaving as thixotropic gels) but also in their spectroscopic behaviour. Fluorescence, in particular, is the technique of election to study this complex set of equilibria. Upon increasing the temperature, DXpol melts into DXdim, which in …