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Title: Crystal Structures of Ln4Ni3O8 (Ln = La, Nd) T′-type Nickelates

Abstract

Single-phase Ln4Ni3O8 (Ln = La, Nd) nickelates were synthesized and their crystal structures were determined by Rietveld refinement of powder neutron diffraction data. The crystal structures of these mixed-valent Ni1+/Ni2+ phases belong to the T'-type and are built by intergrowth of LnO2 fluorite layers with triple NiO2 infinite-layer structural blocks. The major driving force of transformation of the LnO rock-salt block of the parent Ln4Ni3O10-d Ruddlesden-Popper phases to the fluorite arrangement in the reduced Ln4Ni3O8 phases is attributed to internal structural stress. This transformation allows longer Ni-O bonds in Ln4Ni3O8 without overstretching of the Ln-O bonds, especially in the equatorial plane. The observed displacement of Ni atoms from the outer NiO2 planes toward the Ni atom of the central NiO2 plane in Ln4Ni3O8 is ascribed to large electrostatic repulsion from the fluorite part of the structure. X-ray absorption spectra near the K-edge of Ni suggest that the charge density on the nickel ion is similar for all members of the T'-type Lnn+1NinO2n+2 homologous series, which correlates with nearly constant Ni-O bond lengths observed in all the reduced nickelates. This suggests that the formal changes in the valence state of Ni affect the covalency of the Ni-O bond.

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
959866
Report Number(s):
BNL-82852-2009-JA
Journal ID: ISSN 0020-1669; INOCAJ; TRN: US201016%%1010
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Inorganic Chemistry; Journal Volume: 46
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ABSORPTION SPECTRA; ATOMS; BOND LENGTHS; CHARGE DENSITY; COVALENCE; CRYSTAL STRUCTURE; ELECTROSTATICS; FLUORITE; NEUTRON DIFFRACTION; NICKEL IONS; NICKELATES; SALT DEPOSITS; TRANSFORMATIONS; VALENCE; national synchrotron light source

Citation Formats

Poltavets,K., Lokshin, A., Croft, M., Mandal, T., Egami, T., and Greenblatt, M.. Crystal Structures of Ln4Ni3O8 (Ln = La, Nd) T′-type Nickelates. United States: N. p., 2007. Web. doi:10.1021/ic701480v.
Poltavets,K., Lokshin, A., Croft, M., Mandal, T., Egami, T., & Greenblatt, M.. Crystal Structures of Ln4Ni3O8 (Ln = La, Nd) T′-type Nickelates. United States. doi:10.1021/ic701480v.
Poltavets,K., Lokshin, A., Croft, M., Mandal, T., Egami, T., and Greenblatt, M.. Mon . "Crystal Structures of Ln4Ni3O8 (Ln = La, Nd) T′-type Nickelates". United States. doi:10.1021/ic701480v.
@article{osti_959866,
title = {Crystal Structures of Ln4Ni3O8 (Ln = La, Nd) T′-type Nickelates},
author = {Poltavets,K. and Lokshin, A. and Croft, M. and Mandal, T. and Egami, T. and Greenblatt, M.},
abstractNote = {Single-phase Ln4Ni3O8 (Ln = La, Nd) nickelates were synthesized and their crystal structures were determined by Rietveld refinement of powder neutron diffraction data. The crystal structures of these mixed-valent Ni1+/Ni2+ phases belong to the T'-type and are built by intergrowth of LnO2 fluorite layers with triple NiO2 infinite-layer structural blocks. The major driving force of transformation of the LnO rock-salt block of the parent Ln4Ni3O10-d Ruddlesden-Popper phases to the fluorite arrangement in the reduced Ln4Ni3O8 phases is attributed to internal structural stress. This transformation allows longer Ni-O bonds in Ln4Ni3O8 without overstretching of the Ln-O bonds, especially in the equatorial plane. The observed displacement of Ni atoms from the outer NiO2 planes toward the Ni atom of the central NiO2 plane in Ln4Ni3O8 is ascribed to large electrostatic repulsion from the fluorite part of the structure. X-ray absorption spectra near the K-edge of Ni suggest that the charge density on the nickel ion is similar for all members of the T'-type Lnn+1NinO2n+2 homologous series, which correlates with nearly constant Ni-O bond lengths observed in all the reduced nickelates. This suggests that the formal changes in the valence state of Ni affect the covalency of the Ni-O bond.},
doi = {10.1021/ic701480v},
journal = {Inorganic Chemistry},
number = ,
volume = 46,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
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