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Anharmonicity and scissoring modes in the negative thermal expansion materials ScF 3 and CaZrF 6
DOI:
10.1103/PhysRevB.101.064306
Authors:
T. A.
Bird
(University of Warwick)
,
J.
Woodland-Scott
(University of Oxford)
,
L.
Hu
(University of Science and Technology Beijing)
,
M. T.
Wharmby
(Deutsches Elektronen-Synchrotron (DESY))
,
J.
Chen
(University of Science and Technology Beijing)
,
A. L.
Goodwin
(University of Oxford)
,
M. S.
Senn
(University of Warwick)
Co-authored by industrial partner:
No
Type:
Journal Paper
Journal:
Physical Review B
, VOL 101
State:
Published (Approved)
Published:
February 2020
Diamond Proposal Number(s):
18786

Abstract: We use a symmetry-motivated approach to analyzing x-ray pair distribution functions to study the mechanism of negative thermal expansion in two ReO 3 -like compounds: ScF 3 and CaZrF 6 . Both average and local structures suggest that it is the flexibility of M -F- M linkages ( M = Ca, Zr, Sc) due to dynamic rigid and semirigid “scissoring” modes that facilitates the observed negative thermal expansion (NTE) behavior. The amplitudes of these dynamic distortions are greater for CaZrF 6 than for ScF 3 , which corresponds well with the larger magnitude of the thermal expansion reported in the literature for the former. We show that this flexibility is enhanced in CaZrF 6 due to the rocksalt ordering mixing the characters of two of these scissoring modes. Additionally, we show that in ScF 3 anharmonic coupling between the modes responsible for the structural flexibility and the rigid unit modes contributes to the unusually high NTE behavior in this material.
Journal Keywords: Lattice dynamics; Phonons; Structural properties; Thermal expansion
Subject Areas:
Materials,
Physics
Instruments:
I11-High Resolution Powder Diffraction
Other Facilities: P02.1 at PETRA III
Added On:
27/02/2020 09:48
Documents:
h4fg5sss.pdf
Discipline Tags:
Physics
Hard condensed matter - structures
Materials Science
Perovskites
Metallurgy
Technical Tags:
Diffraction
X-ray Powder Diffraction