Ablitt, Chris, Mostofi, Arash A., Bristowe, Nicholas C. and Senn, Mark S. (2018) Control of uniaxial negative thermal expansion in layered perovskites by tuning layer thickness. Frontiers in Chemistry, 6 . 455. doi:10.3389/fchem.2018.00455 ISSN 2296-2646.

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Abstract

Uniaxial negative thermal expansion (NTE) is known to occur in low n members of the An+1BnO3n+1 Ruddlesden–Popper (RP) layered perovskite series with a frozen rotation of BO6 octahedra about the layering axis. Previous work has shown that this NTE arises due to the combined effects of a close proximity to a transition to a competing phase, so called “symmetry trapping”, and highly anisotropic elastic compliance specific to the symmetry of the NTE phase. We extend this analysis to the broader RP family (n = 1, 2, 3, 4, …, ∞), demonstrating that by changing the fraction of layer interface in the structure (i.e., the value of 1/n) one may control the anisotropic compliance that is necessary for the pronounced uniaxial NTE observed in these systems. More detailed analysis of how the components of the compliance matrix develop with 1/n allows us to identify different regimes, linking enhancements in compliance between these regimes to the crystallographic degrees of freedom in the structure. We further discuss how the perovskite layer thickness affects the frequencies of soft zone boundary modes with large negative Grüneisen parameters, associated with the aforementioned phase transition, that constitute the thermodynamic driving force for NTE. This new insight complements our previous work—showing that chemical control may be used to switch from positive to negative thermal expansion in these systems—since it makes the layer thickness, n, an additional design parameter that may be used to engineer layered perovskites with tuneable thermal expansion. In these respects, we predict that, with appropriate chemical substitution, the n = 1 phase will be the system in which the most pronounced NTE could be achieved.

Item Type:	Journal Article
Subjects:	Q Science > QD Chemistry Q Science > QE Geology
Divisions:	Faculty of Science, Engineering and Medicine > Science > Chemistry
Library of Congress Subject Headings (LCSH):	Perovskite, Anisotropy, Expansion (Heat)
Journal or Publication Title:	Frontiers in Chemistry
Publisher:	Frontiers Research Foundation
ISSN:	2296-2646
Official Date:	18 October 2018
Dates:	Date Event 18 October 2018 Published 13 September 2018 Accepted
Volume:	6
Article Number:	455
DOI:	10.3389/fchem.2018.00455
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Open Access (Creative Commons)
Date of first compliant deposit:	19 October 2018
Date of first compliant Open Access:	19 October 2018
RIOXX Funder/Project Grant:	Project/Grant ID RIOXX Funder Name Funder ID EP/L015579/1 [EPSRC] Engineering and Physical Sciences Research Council http://dx.doi.org/10.13039/501100000266 TYC-101 Thomas Young Centre http://dx.doi.org/10.13039/501100004402 EP/P020194/1 [EPSRC] Engineering and Physical Sciences Research Council http://dx.doi.org/10.13039/501100000266

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