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Title: Heat-Induced Phase Transformation of Three-Dimensional Nb3O7(OH) Superstructures: Effect of Atmosphere and Electron Beam

Abstract

Nanostructured niobium oxides and hydroxides are potential candidates for photochemical applications due to their excellent optical and electronic properties. In the present work the thermal stability of Nb3O7(OH) superstructures prepared by a simple hydrothermal approach is investigated at the atomic scale. Transmission electron microscopy and electron energy-loss spectroscopy provide insights into the phase transformation occurring at elevated temperatures and probe the effect of the atmospheric conditions. In the presence of oxygen, H2O is released from the crystal at temperatures above 500 °C, and the crystallographic structure changes to H-Nb2O5. In addition to the high thermal stability of Nb3O7(OH), the morphology was found to be stable, and first changes in the form of a merging of nanowires are not observed until 850 °C. Under reducing conditions in a transmission electron microscope and during electron beam bombardment, an oxygen-deficient phase is formed at temperatures above 750 °C. This transformation starts with the formation of defects in the crystal lattice at 450 °C and goes along with the formation of pores in the nanowires which accommodate the volume differences of the two crystal phases.

Authors:
 [1];  [2];  [3];  [3];  [2];  [4]
  1. Ludwig-Maximilians-Univ., Munich (Germany). Dept. of Chemistry and Center for NanoScience; Nanosystems Initiative Munich, Munich (Germany)
  2. Max-Planck-Inst. für Eisenforschung GmbH, Düsseldorf (Germany)
  3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). National Center for Electron Microscopy, Molecular Foundry
  4. Max-Planck-Inst. für Eisenforschung GmbH, Düsseldorf (Germany); Nanosystems Initiative Munich, Munich (Germany)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1506258
Grant/Contract Number:  
AC02-05CH11231
Resource Type:
Accepted Manuscript
Journal Name:
Crystal Growth and Design
Additional Journal Information:
Journal Volume: 16; Journal Issue: 8; Journal ID: ISSN 1528-7483
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Betzler, Sophia B., Harzer, Tristan, Ciston, Jim, Dahmen, Ulrich, Dehm, Gerhard, and Scheu, Christina. Heat-Induced Phase Transformation of Three-Dimensional Nb3O7(OH) Superstructures: Effect of Atmosphere and Electron Beam. United States: N. p., 2016. Web. doi:10.1021/acs.cgd.6b00386.
Betzler, Sophia B., Harzer, Tristan, Ciston, Jim, Dahmen, Ulrich, Dehm, Gerhard, & Scheu, Christina. Heat-Induced Phase Transformation of Three-Dimensional Nb3O7(OH) Superstructures: Effect of Atmosphere and Electron Beam. United States. doi:10.1021/acs.cgd.6b00386.
Betzler, Sophia B., Harzer, Tristan, Ciston, Jim, Dahmen, Ulrich, Dehm, Gerhard, and Scheu, Christina. Fri . "Heat-Induced Phase Transformation of Three-Dimensional Nb3O7(OH) Superstructures: Effect of Atmosphere and Electron Beam". United States. doi:10.1021/acs.cgd.6b00386. https://www.osti.gov/servlets/purl/1506258.
@article{osti_1506258,
title = {Heat-Induced Phase Transformation of Three-Dimensional Nb3O7(OH) Superstructures: Effect of Atmosphere and Electron Beam},
author = {Betzler, Sophia B. and Harzer, Tristan and Ciston, Jim and Dahmen, Ulrich and Dehm, Gerhard and Scheu, Christina},
abstractNote = {Nanostructured niobium oxides and hydroxides are potential candidates for photochemical applications due to their excellent optical and electronic properties. In the present work the thermal stability of Nb3O7(OH) superstructures prepared by a simple hydrothermal approach is investigated at the atomic scale. Transmission electron microscopy and electron energy-loss spectroscopy provide insights into the phase transformation occurring at elevated temperatures and probe the effect of the atmospheric conditions. In the presence of oxygen, H2O is released from the crystal at temperatures above 500 °C, and the crystallographic structure changes to H-Nb2O5. In addition to the high thermal stability of Nb3O7(OH), the morphology was found to be stable, and first changes in the form of a merging of nanowires are not observed until 850 °C. Under reducing conditions in a transmission electron microscope and during electron beam bombardment, an oxygen-deficient phase is formed at temperatures above 750 °C. This transformation starts with the formation of defects in the crystal lattice at 450 °C and goes along with the formation of pores in the nanowires which accommodate the volume differences of the two crystal phases.},
doi = {10.1021/acs.cgd.6b00386},
journal = {Crystal Growth and Design},
number = 8,
volume = 16,
place = {United States},
year = {2016},
month = {7}
}

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Figures / Tables:

Figure 1 Figure 1: Electron micrographs of samples heated ex situ under ambient conditions. (a) SEM image of the Nb3O7(OH) superstructure before the calcination and after the calcination at 850 °C (b) and 1200 °C (c). (d) TEM image of the network consisting of the Nb3O7(OH) nanowires before calcination. (e) TEM imagemore » of the nanowire network obtained after calcination at 850 °C. The electron diffraction pattern recorded for one nanocrystal in the [001] zone axis is shown in (f). (g) High resolution TEM (HRTEM) image of an area which shows that the nanowires merged to form larger crystals during calcination at 850 °C. The white lines indicate individual grains. (h) Magnified view of the boundary between two nanowires grown together. A miss-tilt of 4° also visible in the fast Fourier transformation (FFT) is compensated by dislocations (highlighted with white lines) arranged in a small angle grain boundary (SAGB).« less

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