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Title: Oxygen-storage behavior and local structure in Ti-substituted YMnO 3

Abstract

Hexagonal manganates RMnO3 (R=Y, Ho, Dy) have been recently shown to exhibit oxygen-storage capacities promising for three-way catalysts, air-separation, and related technologies. Here, we demonstrate that Ti substitution for Mn can be used to chemically tune the oxygen-breathing properties of these materials towards practical applications. Specifically, Y(Mn1-xTix)O3 solid solutions exhibit facile oxygen absorption/desorption via reversible Ti3+↔Ti4+ and Mn3+↔Mn4+ reactions already in ambient air at ≈400 °C and ≈250 °C, respectively. On cooling, the oxidation of both cations is accompanied by oxygen uptake yielding a formula YMn3+1-x-yMn4+yTi4+xO3+δ. The presence of Ti promotes the oxidation of Mn3+ to Mn4+, which is almost negligible for YMnO3 in air, thereby increasing the uptake of oxygen beyond that required for a given Ti4+ concentration. The reversibility of the redox reactions is limited by sluggish kinetics; however, the oxidation process continues, if slowly, even at room temperature. The extra oxygen atoms are accommodated by the large interstices within a triangular lattice formed by the [MnO5] trigonal bipyramids. According to bond distances from Rietveld refinements using the neutron diffraction data, the YMnO3 structure features under-bonded Mn and even more severely under-bonded oxygen atoms that form the trigonal bases of the [MnO5] bipyramids. The tensile bond strain aroundmore » the 5-fold coordinated Mn site and the strong preference of Ti4+(and Mn4+) for higher coordination numbers likely provide driving forces for the oxidation reaction. Reverse Monte Carlo refinements of the local atomic displacements using neutron total scattering revealed how the excess oxygen atoms are accommodated in the structure by correlated local displacements of the host atoms. Large displacements of the under-bonded host oxygen atoms play a key part in this lattice-relaxation process, facilitating reversible exchange of significant amounts of oxygen with atmosphere.« less

Authors:
; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1409579
Report Number(s):
BNL-114631-2017-JA¿¿¿
Journal ID: ISSN 0022-4596
DOE Contract Number:  
SC0012704
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 246; Journal Issue: C
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Levin, I., Krayzman, V., Vanderah, T. A., Tomczyk, M., Wu, H., Tucker, M. G., Playford, H. Y., Woicik, J. C., Dennis, C. L., and Vilarinho, P. M.. Oxygen-storage behavior and local structure in Ti-substituted YMnO 3. United States: N. p., 2017. Web. doi:10.1016/j.jssc.2016.10.029.
Levin, I., Krayzman, V., Vanderah, T. A., Tomczyk, M., Wu, H., Tucker, M. G., Playford, H. Y., Woicik, J. C., Dennis, C. L., & Vilarinho, P. M.. Oxygen-storage behavior and local structure in Ti-substituted YMnO 3. United States. doi:10.1016/j.jssc.2016.10.029.
Levin, I., Krayzman, V., Vanderah, T. A., Tomczyk, M., Wu, H., Tucker, M. G., Playford, H. Y., Woicik, J. C., Dennis, C. L., and Vilarinho, P. M.. Wed . "Oxygen-storage behavior and local structure in Ti-substituted YMnO 3". United States. doi:10.1016/j.jssc.2016.10.029.
@article{osti_1409579,
title = {Oxygen-storage behavior and local structure in Ti-substituted YMnO 3},
author = {Levin, I. and Krayzman, V. and Vanderah, T. A. and Tomczyk, M. and Wu, H. and Tucker, M. G. and Playford, H. Y. and Woicik, J. C. and Dennis, C. L. and Vilarinho, P. M.},
abstractNote = {Hexagonal manganates RMnO3 (R=Y, Ho, Dy) have been recently shown to exhibit oxygen-storage capacities promising for three-way catalysts, air-separation, and related technologies. Here, we demonstrate that Ti substitution for Mn can be used to chemically tune the oxygen-breathing properties of these materials towards practical applications. Specifically, Y(Mn1-xTix)O3 solid solutions exhibit facile oxygen absorption/desorption via reversible Ti3+↔Ti4+ and Mn3+↔Mn4+ reactions already in ambient air at ≈400 °C and ≈250 °C, respectively. On cooling, the oxidation of both cations is accompanied by oxygen uptake yielding a formula YMn3+1-x-yMn4+yTi4+xO3+δ. The presence of Ti promotes the oxidation of Mn3+ to Mn4+, which is almost negligible for YMnO3 in air, thereby increasing the uptake of oxygen beyond that required for a given Ti4+ concentration. The reversibility of the redox reactions is limited by sluggish kinetics; however, the oxidation process continues, if slowly, even at room temperature. The extra oxygen atoms are accommodated by the large interstices within a triangular lattice formed by the [MnO5] trigonal bipyramids. According to bond distances from Rietveld refinements using the neutron diffraction data, the YMnO3 structure features under-bonded Mn and even more severely under-bonded oxygen atoms that form the trigonal bases of the [MnO5] bipyramids. The tensile bond strain around the 5-fold coordinated Mn site and the strong preference of Ti4+(and Mn4+) for higher coordination numbers likely provide driving forces for the oxidation reaction. Reverse Monte Carlo refinements of the local atomic displacements using neutron total scattering revealed how the excess oxygen atoms are accommodated in the structure by correlated local displacements of the host atoms. Large displacements of the under-bonded host oxygen atoms play a key part in this lattice-relaxation process, facilitating reversible exchange of significant amounts of oxygen with atmosphere.},
doi = {10.1016/j.jssc.2016.10.029},
journal = {Journal of Solid State Chemistry},
number = C,
volume = 246,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}
}