Phase change and pyroelectricity in natural hemimorphite

The phase change of a natural hemimorphite sample from Minas Gerais (Brazil) was investigated by two X-ray diffraction (XRD) methods and by near-infrared reflectance spectroscopy. Applying successive thermal treatments, the crystal structure undergoes two orientation conversions. The first one occurs at about 550 degrees C, and it was revealed by the Laue method. Below 500 degrees C, the water molecules were partially expelled without changing the crystal structure. A fact that supports this statement is the sequential disappearance of the water bands at 1400 and 1900 nm by thermal treatment. The second conversion takes place below 939 degrees C. Moreover, at 972 degrees C a phase change to the willemite mineral (alpha-Zn(2)SiO(4)) has been observed. This last conversion was confirmed by the power XRD. In addition, natural hemimorphite displayed a high pyroelectricity, which is related both to the absence of inverse centre and to the presence of molecular water and hydroxyl groups in the crystal structure.

First evidence of crystalline KHSO(4):Mn grown by an aqueous solution method and the investigation of the effect of ionizing radiation exposure

In this work, KHSO(4):Mn crystals doped with Mn and K(2)SO(4) were synthesized using an aqueous solution method. The samples were exposed to ionizing radiation in order to observe the effects on their physical properties. Raman spectroscopy was used to identify the structure of the crystals by detecting the vibrational frequencies of the crystalline lattice. Electron paramagnetic resonance (EPR) was used to study the creation of paramagnetic centers arising from exposure to ionizing radiation. This new synthesis method produces high quality K(2)SO(4) and KHSO(4):Mn crystals and allows control of structural, morphological, optical and magnetic properties. (C) 2009 Elsevier B.V. All rights reserved,

Joint Experimental and Theoretical Analysis of Order Disorder Effects in Cubic BaZrO(3) Assembled Nanoparticles under Decaoctahedral Shape

Periodic first-principles calculations based on density functional theory at the B3LYP level has been carried out to investigate the photoluminescence (PL) emission of BaZrO(3) assembled nanoparticles at room temperature. The defect created in the nanocrystals and their resultant electronic features lead to a diversification of electronic recombination within the BaZrO(3) band gap. Its optical phenomena are discussed in the light of photoluminescence emission at the green-yellow region around 570 nm. The theoretical model for displaced atoms and/or angular changes leads to the breaking of the local symmetry, which is based on the refined structure provided by Rietveld methodology. For each situation a band structure, charge mapping, and density of states were built and analyzed. X-ray diffraction (XRD) patterns, UV-vis measurements, and field emission scanning electron microscopy (FE-SEM) images are essential for a full evaluation of the crystal structure and morphology.

Adsorption Behavior of 5-Fluorouracil on Au(111): An In Situ STM Study

The biological effects of chemical substitution of DNA bases triggered several investigations of their physicochemical properties This paper studies the adsorption behavior of a halogenated uracil, 5-fluorouracil (5FU). at the electrochemical interface of Au(111) and sulfuric acid solution. Upon modulation of the electric field across the interface, four distinct phases could be inferred by means of cyclic voltammetry (CV) At negative potentials relative to the SCE electrode, limited by the threshold of hydrogen evolution, no molecular species could be detected by scanning tunneling microscopy (STM) at the reconstructed Au(111)-(23 x root 3) surface, indicating that any physisorbed molecules are randomly distributed Incursion into more positive potentials increases the surface population but doer not form any two-dimensional (2D) physisorbed ordered structure Instead, we observed metastable structures that are only detectable. on surfaces with high defect density At sufficiently high positive potentials. limited by gold oxidation, the molecules are chemisorbed in a (3 x 2 root 3) ordered structure. with the aromatic ring perpendicular to the surface We report the densest chemisorbed monolayer for pyrimidine-derivative molecules (area per molecule 0 14 +/- 0 04 nm(2)). A comparison of the adsorption behavior of uracil derivatives has been made based on recent results of chemical substitution and solvent effects. We propose that pi-stacking is enhanced when halogens are incorporated in the uracil structure, in a similar fashion to what is observed in then crystal structure

Dependence of the product on the P-P ligand in reactions of [RuCl(3)(NO)(P-P)] complexes (P-P = aromatic diphosphines) with 2-mercaptopyridine

This study presents the syntheses and characterization of 2-mercaptopyridine (pyS(-)) complexes containing ruthenium(II) with the following general formula [Ru(pyS)(2)(P-P)], P-P = (c-dppen) = cis-1,2-bis(diphenylphosphino)ethylene) (1); (dppe)=1,2-bis(diphenylphosphino)ethane (2); (dppp)=1,3-bis(diphenylphosphino)propane (3) and (dppb) = 1,4-bis(diphenylphosphino)butane (4). The complexes were synthesized from the mer- or fac-[RuCl(3)(NO)(P-P)] precursors in the presence of triethylamine in methanol solution with dependence of the product on the P-P ligand. The reaction of pyS- with a ruthenium complex containing a bulky aromatic diphosphine dppb disclosed a major product with a dangling coordinated dppbO-P, the [Ru(pyS)(2)(NO)(eta(1)-dppbO-P)]PF(6) (5). In addition, this work also presents and discusses the spectroscopic and electrochemical behavior of 1-5. and report the X-ray structures for I and S. (C) 2009 Elsevier Ltd. All rights reserved.