Solid state transitions of Bi 2 O 3 nanoparticles
- PDF / 433,287 Bytes
- 10 Pages / 584.957 x 782.986 pts Page_size
- 96 Downloads / 197 Views
Olivier Guillona) Otto Schott Institute of Materials Research, Friedrich Schiller University of Jena, Jena 07743, Germany (Received 21 December 2013; accepted 29 May 2014)
The solid-state phase transitions of bismuth(III) oxide (Bi2O3) nanoparticles were investigated by complementary methods such as differential scanning calorimetry, differential thermal analysis with combined thermogravimetry and mass spectrometry, and high-temperature x-ray diffraction as compacted nanopowder. At room temperature the particles resided in the b-phase, which is usually a metastable high-temperature phase of bulk Bi2O3. The complementary experimental methods were linked and a nanophase (tetragonal b-phase) ! bulk-phase (monoclinic a-phase) transition was identified which was preceded by crystal growth and evaporation of O and C containing species. It was also shown that the atmosphere (more precisely its absolute pressure) has an influence on the transition behavior. An interpretation was proposed that successfully explains all observations from this work and from literature: A sudden destabilization takes place around 735 K due to the loss of the stabilizing, carbonized surface. This leads to the observed transformation to the bulk-phase. But if the particles are smaller than a certain, critical size in the nanorange and are not allowed to grow, they remain in the nanophase until they melt.
I. INTRODUCTION
Size-dependent melting and evaporation are theoretically and experimentally validated phenomena.1 On the other hand temperature-induced solid state transitions at the nanoscale have been reported, but inadvertent particle reorganization, sublimation, or sintering change the dispersion and obstruct the experimental observation. Rivest et al. recently showed the size-dependent solid– solid transition of low-chalcocite to high-chalcocite copper(I) sulfide nanorods scattered on a substrate.2 They found a similar 1/D dependence of the transition temperature-like in melting of nanoparticles.1 Baldinozzi et al.3 investigated up to 680 °C the structure of nanocrystalline zirconia according to grain size using high-resolution neutron diffraction. They measured that the tetragonal volume fraction is nearly 100% for 10-nm particles, whereas it is only 50% for 60-nm ones. Curve extrapolation suggests no tetragonality above 200 nm. Suresh et al. also found a size dependency of the solid–solid phase transformation from the tetragonal to monoclinic form for yttria stabilized zirconia nanoparticles.4 The proposed model relies on size dependent a)
Address all correspondence to this author. e-mail: [email protected] Present address: Institute of Energy and Climate Research, IEK-1: Materials Synthesis and Processing, Forschungszentrum Jülich GmbH, Jülich, Germany DOI: 10.1557/jmr.2014.124 J. Mater. Res., Vol. 29, No. 12, Jun 28, 2014
http://journals.cambridge.org
Downloaded: 16 Jul 2014
chemical potentials developed for the melting of nanoparticles. Navrotsky et al.5–8 quantitatively showed the size-dependent polymorphism and drew phase di
Data Loading...
