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

The ball milling induced transformation of alpha-Fe2O3 powder in air and oxygen atmosphere

The mechanochemical treatment of alpha-Fe2O3 powder was done concurrently in air and oxygen atmospheres using a conventional planetary ball mill. The influence of the duration of milling and of the balls-to-powder mass ratio on the transformation of alpha-Fe2O3 was investigated. Under appropriate milling conditions, alpha-Fe2O3, completely transforms to Fe3O4, and for prolonged milling to the Fe-1 _ O-x phase, either in air or oxygen atmosphere. Owing to the higher oxygen pressure, the start of the reaction in oxygen is delayed by similar to 1 h in comparison with the reaction in air. The reverse mechanochemical reaction Fe-1 . O-- GT Fe3O4-- GT , alpha-Fe2O3 takes place under proper oxygen atmosphere. The oxygen partial pressure is the critical parameter responsible for the mechanochemical reactions. The balls-to-powder mass ratio has a considerable influence on the kinetics of mechanochemical reactions. Below the threshold value the reaction does not proceed or proceeds very slowly. Plausibly, three phenomena govern mechanochemical reactions: (i) the generation of highly energetic and localized sites of a short lifetime at the moment of impact; (ii) the adsorption of oxygen at atomically dean surfaces created by particle fracture; and (iii) the change of activities of the constituent phases arising from a very distorted (nanocrystalline) structure. (C) 1999 Elsevier Science S.A. All rights reserved

Dielectric and ferroelectric properties of BaTi1-xSnxO3 multilayered ceramics

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