Kowalczyk, Radoslaw M., Kemp, Thomas F., Walker, David, Pike, Kevin J., Thomas, Pam A., Kreisel, J., Dupree, Ray, Newton, Mark E., Hanna, John V. and Smith, Mark E. (2011) A variable temperature solid-state nuclear magnetic resonance, electron paramagnetic resonance and Raman scattering study of molecular dynamics in ferroelectric fluorides. Journal of Physics: Condensed Matter, Vol.23 (No.31). Article 315402. doi:10.1088/0953-8984/23/31/315402 ISSN 0953-8984.

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Abstract

The local nuclear and electronic structures and molecular dynamics of the ferroelectric lattice in selected geometric fluorides (BaMgF(4), BaZnF(4), BaMg(1-x)Mn(x)F(4) and BaMg(1-x)Ni(x)F(4); x = 0.001 and 0.005) have been investigated. The (19)F and (25)Mg isotropic chemical shift delta(iso), (25)Mg quadrupolar coupling constants (C(q)) and asymmetry parameters (eta) reflect the geometry of the coordination spheres. The zero-field splitting parameters vertical bar D vertical bar and vertical bar E vertical bar are consistent with distorted axial symmetry (low temperatures) and nearly rhombic symmetry (high temperatures) of octahedral Mn(2+) coordination. The high resolution of the nuclear magnetic resonance, electron paramagnetic resonance and phonon spectra are consistent with the highly ordered crystallographic structure. Combined multi-technique data evidence the subtle discontinuous changes in the temperature dependences of vertical bar D vertical bar and vertical bar E vertical bar, isotropic chemical shifts delta(iso) and signature parameters of Raman bands and suggest a discontinuous structural distortion of the fluoride octahedra. The temperature at which this change occurs depends on the ionic radius of the central ion of the octahedral site and is estimated to be similar to 300 K for Zn(2+) fluorides and similar to 240 K for Mg(2+) fluorides. This geometrical distortion modifies the lattice dynamics and originates from the rotation of the fluoride octahedra around a new direction approximately perpendicular to that related to the paraelectric-ferroelectric phase transition.

Item Type:	Journal Article
Subjects:	Q Science > QC Physics
Divisions:	Administration > University Executive Office Faculty of Science, Engineering and Medicine > Science > Physics
Library of Congress Subject Headings (LCSH):	Fluorides -- Analysis, Ferroelectricity
Journal or Publication Title:	Journal of Physics: Condensed Matter
Publisher:	Institute of Physics Publishing Ltd.
ISSN:	0953-8984
Official Date:	2011
Dates:	Date Event 2011 Published
Volume:	Vol.23
Number:	No.31
Page Range:	Article 315402
DOI:	10.1088/0953-8984/23/31/315402
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access
Date of first compliant deposit:	18 December 2015
Date of first compliant Open Access:	18 December 2015
Funder:	University of Warwick, British Council, Advantage West Midlands (AWM), European Regional Development Fund (ERDF), Engineering and Physical Sciences Research Council (EPSRC), Birmingham Science City
Grant number:	RD08145 (UoW), EP/D045967 (EPSRC)

Data sourced from Thomson Reuters' Web of Knowledge

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