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  4. Chemical exchange at the ferroelectric phase transition of lead germanate revealed by solid state Pb-207 nuclear magnetic resonance
 
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research article

Chemical exchange at the ferroelectric phase transition of lead germanate revealed by solid state Pb-207 nuclear magnetic resonance

Avalos, Claudia E.  
•
Walder, Brennan J.  
•
Viger-Gravel, Jasmine
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January 21, 2019
Physical Chemistry Chemical Physics

The nature of the dynamics and structural changes that take place at the ferroelectric phase transition in lead oxides is a rich field of study. Solid-state nuclear magnetic resonance (NMR) of Pb-207 is well suited to study the local structure and disorder in lead oxide ferroelectric transitions at the atomic level. However, very large Pb-207 shielding anisotropy results in poor resolution in 1D static and magic angle spinning (MAS) NMR spectra. We address this problem by using short high-power adiabatic pulses (SHAPs) with magic-angle-turning sequences to correlate the isotropic and anisotropic parts of the Pb-207 chemical shift tensor in a 2D NMR experiment, yielding resolved Pb-207 NMR spectra of the nine distinct lead sites in uniaxial ferroelectric lead germanate (Pb5Ge3O11). Using this technique we detect the magnetic environments of displaced Pb2+ ions and unambiguously identify the nature of the phase transition as mixed displacive and order-disorder. We also observe that the atomic-level process responsible for the phase transition in ferroelectric lead germanate is chemical exchange on the kilohertz timescale. We derive an activation energy of 103.4 +/- 1.7 kJ mol(-1) and compare it to dielectric spectroscopy studies on similar materials. These results show that this method can be used to characterize ferroelectric phase transitions of complex materials with high resolution using nuclei that are typically inaccessible due to their large shielding anisotropy.

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Type
research article
DOI
10.1039/c8cp06507a
Web of Science ID

WOS:000456147000010

Author(s)
Avalos, Claudia E.  
•
Walder, Brennan J.  
•
Viger-Gravel, Jasmine
•
Magrez, Arnaud  
•
Emsley, Lyndon  
Date Issued

2019-01-21

Publisher

ROYAL SOC CHEMISTRY

Published in
Physical Chemistry Chemical Physics
Volume

21

Issue

3

Start page

1100

End page

1109

Subjects

Chemistry, Physical

•

Physics, Atomic, Molecular & Chemical

•

Chemistry

•

Physics

•

crystal-structure

•

raman-scattering

•

order-disorder

•

nmr

•

shifts

•

perovskites

•

frequency

•

pb5ge3o11

•

behavior

•

origin

Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
LRM  
Available on Infoscience
February 1, 2019
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/154288
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