Isostructural second-order phase transition of b-Bi2O3 at high pressures: an experimental and theoretical study

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of Physical Chemistry C, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/jp507826jWe report a joint experimental and theoretical study of the structural and vibrational properties of synthetic sphaerobismoite (beta-Bi2O3) at high pressures in which room-temperature angle-dispersive X-ray diffraction (XRD) and Raman scattering measurements have been complemented with ab initio total energy and lattice dynamics calculations. Striking changes in Raman spectra were observed around 2 GPa, whereas X-ray diffraction measurements evidence no change in the tetragonal symmetry of the compound up to 20 GPa; however, a significant change exists in the compressibility when increasing pressure above 2 GPa. These features have been understood by means of theoretical calculations, which show that beta-Bi2O3 undergoes a pressure-induced isostructural phase transition near 2 GPa. In the new isostructural beta' phase, the Bi3+ and O2- environments become more regular than those in the original beta phase because of the strong decrease in the activity of the lone electron pair of Bi above 2 GPa. Raman measurements and theoretical calculations provide evidence of the second-order nature of the pressure-induced isostructural transition. Above 20 GPa, XRD measurements suggest a partial amorphization of the sample despite Raman measurements still show weak peaks, probably related to a new unknown phase which remains up to 27 GPa. On pressure release, XRD patterns and Raman spectra below 2 GPa correspond to elemental Bi-I, thus evidencing a pressure-induced decomposition of the sample during downstroke.Financial support from the Spanish Consolider Ingenio 2010 Program (MALTA Project CSD2007-00045) is acknowledged. This work was also supported by Brazilian Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq) under Project 201050/2012-9, Spanish MICINN under Projects MAT2010-21270-004-01/03/04 and MAT2013-46649-C4-2/3/4-P, Spanish MINECO under Project CTQ2012-36253-C03-02, and from Vicerrectorado de Investigacion de la Universitat Politecnica de Valencia under Projects UPV2011-0914 PAID-05-11 and UPV2011-0966 PAID-06-11. Supercomputer time has been provided by the Red Espanola de Supercomputacion (RES) and the MALTA cluster. JAS. acknowledges Juan de la Cierva fellowship program for financial support.Pereira, ALJ.; Sans Tresserras, JÁ.; Vilaplana Cerda, RI.; Gomis, O.; Manjón Herrera, FJ.; Rodriguez-Hernandez, P.; Muñoz, A.... (2014). Isostructural second-order phase transition of b-Bi2O3 at high pressures: an experimental and theoretical study. Journal of Physical Chemistry C. 118(40):23189-23201. https://doi.org/10.1021/jp507826jS23189232011184

Amorphization in zircon: evidence for direct impact damage

X-ray diffraction has been used to characterize the amorphous phase present in a series of radiation-damaged natural zircons with radiation doses ranging from 0.06 to 16 × 1018 -decay events g-1 . The fraction of amorphous material present in each of the samples studied has been determined, and its dependence on the radiation dose has been calibrated. Direct determination of the amorphous fraction confirms that amorphization in natural zircon occurs as a consequence of the direct impact within cascades caused by -recoil nuclei. These results are not consistent with the commonly accepted double-overlap model of damage accumulation. The volume swelling of amorphous regions changes as a function of dose. Thus, the density of amorphous regions depends on the degree of damage up to a certain point (i.e. 8 × 1018 -decay events g-1 ), unlike in previous models for which a constant value independent of the radiation dose was assumed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48881/2/c01106.pd

Quantifying Vegetation Biophysical Variables from Imaging Spectroscopy Data: A Review on Retrieval Methods

An unprecedented spectroscopic data stream will soon become available with forthcoming Earth-observing satellite missions equipped with imaging spectroradiometers. This data stream will open up a vast array of opportunities to quantify a diversity of biochemical and structural vegetation properties. The processing requirements for such large data streams require reliable retrieval techniques enabling the spatiotemporally explicit quantification of biophysical variables. With the aim of preparing for this new era of Earth observation, this review summarizes the state-of-the-art retrieval methods that have been applied in experimental imaging spectroscopy studies inferring all kinds of vegetation biophysical variables. Identified retrieval methods are categorized into: (1) parametric regression, including vegetation indices, shape indices and spectral transformations; (2) nonparametric regression, including linear and nonlinear machine learning regression algorithms; (3) physically based, including inversion of radiative transfer models (RTMs) using numerical optimization and look-up table approaches; and (4) hybrid regression methods, which combine RTM simulations with machine learning regression methods. For each of these categories, an overview of widely applied methods with application to mapping vegetation properties is given. In view of processing imaging spectroscopy data, a critical aspect involves the challenge of dealing with spectral multicollinearity. The ability to provide robust estimates, retrieval uncertainties and acceptable retrieval processing speed are other important aspects in view of operational processing. Recommendations towards new-generation spectroscopy-based processing chains for operational production of biophysical variables are given

Coordination chemistry of homoatomic ligands of bismuth, selenium and tellurium

Multi-centre-bonds as well as conventional two-centre two-electron bonds are the basis for charged or uncharged homoatomic molecules of the heavy main-group elements bismuth, selenium and tellurium. In many cases these homoatomic species are not fairly isolated in the structures but make use of their paired or unpaired p-electrons and, if available, of their pi-systems to establish (strong) heteropolar covalent donor bonds to metal cations. Such coordination can have retroactive effect on the bonding inside the ligand and even stabilises new homonuclear species such as the Bi-10(4+) antiprism or the Te-10-tricycle. Moreover, these homoatomic ligands can be highly connecting, since all of their atoms are potential donors. Here we give an overview of recent developments in the coordination chemistry of oligo- and polyatomic selenium, tellurium and bismuth ligands. (C) 2014 Elsevier B.V. All rights reserved

Reprint of "Coordination chemistry of homoatomic ligands of bismuth, selenium and tellurium"

Multi-centre-bonds as well as conventional two-centre two-electron bonds are the basis for charged or uncharged homoatomic molecules of the heavy main-group elements bismuth, selenium and tellurium. In many cases these homoatomic species are not fairly isolated in the structures but make use of their paired or unpaired p-electrons and, if available, of their pi-systems to establish (strong) heteropolar covalent donor bonds to metal cations. Such coordination can have retroactive effect on the bonding inside the ligand and even stabilises new homonuclear species such as the Bi-10(4+) antiprism or the Te-10-tricycle. Moreover, these homoatomic ligands can be highly connecting, since all of their atoms are potential donors. Here we give an overview of recent developments in the coordination chemistry of oligo- and polyatomic selenium, tellurium and bismuth ligands. (C) 2015 Published by Elsevier B.V