Mihailova
Mihailova
Mihailova
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1. Berichtskolloquium des SPP 1236, 01.10.07 – 03.10.07, Hünfeld<br />
High pressure-induced pressure induced renormalization phenomena<br />
in lead scandium niobates and tantalates<br />
with relaxor behaviour<br />
Principal investigator: Boriana <strong>Mihailova</strong><br />
Co-investigator: Ulrich Bismayer<br />
(project MI 1127/2-1)<br />
Universität Hamburg<br />
Mineralogisch-Petrographisches Institut
Co-workers Co workers and collaborators<br />
University of Hamburg<br />
Prof Dr Boriana <strong>Mihailova</strong> (JP), Prof Dr Ulrich Bismayer<br />
PhD student Anna-Maria Welsch<br />
Dr Carsten Paulmann, Dr Thomas Malcherek<br />
Virginia Tech<br />
Prof Dr Ross Angel<br />
Dr Jing Zhao, Dr Jens Engel<br />
Bulgarian Academy of Sciences<br />
Prof Dr Marin Gospodinov<br />
PTB Braunschweig<br />
Dr Bernd Güttler, Dr Rainer Stosch
Outline<br />
1. Relaxor ferroelectrics<br />
structural peculiarities and open questions<br />
2. Pressure-induced structural transformations<br />
PbSc 0.5Ta 0.5O 3 and Pb 0.78 Ba 0.22 Sc 0.5 Ta 0.5 O 3<br />
(AP - 9 GPa, RT)<br />
3. Our research plan for next 12 months
Relaxor ferroelectrics vs proper ferroelectrics<br />
proper FE PbTiO3 10 3 ε<br />
8<br />
6<br />
4<br />
2<br />
673<br />
FE<br />
773<br />
Temperature / K<br />
dielectric permittivity ε<br />
PE<br />
873<br />
relaxor FE<br />
10 3 ε<br />
Temperature / K<br />
PbMg 1/3Nb 2/3O 3<br />
high ε in relatively wide T range near RT<br />
→ multifunctionality!
Relaxor ferroelectrics – complex nanoscale structure<br />
Proper ferroelectrics<br />
T c ~ T m<br />
paraelectric<br />
ferroelectric<br />
long-range ferroelectric ordering<br />
(length of coherent atomic shifts >> a 0)<br />
T c ≤ T m<br />
Relaxor ferroelectrics<br />
T B<br />
T m<br />
Δα r ~ 0.1°<br />
pseudo-PE<br />
uncoupled atomic shifts<br />
Burns temperature (non-linearity in n(T))<br />
randomly oriented<br />
polar nanoclusters<br />
dielectric permittivity maximum<br />
coupled polar<br />
nanoclusters<br />
canonical<br />
relaxors
Relaxor ferroelectrics – open questions<br />
Atomistic nature of relaxor behaviour<br />
Can we tune relaxor properties<br />
by tailoring polar nanoclusters?<br />
nanoclusters?<br />
• Which is the driving force for nucleation of polar nanoclusters at HT?<br />
• What is the reason for suppression of ferroelectric long-range ordering at LT?<br />
local electric fields due to charge imbalance<br />
local elastic fields due to local structural distortions<br />
The majority of relaxors :<br />
Pb-based perovskite-type oxides<br />
(Pb,A”)(B’,B”)O 3<br />
performance<br />
structure<br />
properties<br />
processing
Our general goals<br />
Raman scattering and X-ray ray diffraction on single crystals<br />
PbSc0.5Ta0.5O3 (PST)<br />
and<br />
PbSc0.5Nb0.5O3 (PSN)<br />
A-site-doped PST and PSN,<br />
substitution of Ba 2+ , La 3+ , Bi 3+ for Pb 2+<br />
Nb-doped PST, substitution of Nb 5+ for Ta 5+<br />
High-pressure<br />
High pressure studies on relaxors of type PbB’ 0.5B” 0.5O3 :<br />
- atomic clustering under pressure<br />
- pressure-induced phase transitions<br />
AB’ 1/2 B” 1/2 O 3<br />
AB’ 1/3 B” 2/3 O 3<br />
- changes in the compression behaviour upon doping
Relaxors – phonon anomalies at ambient p and T<br />
prototype structure Fm3m<br />
F1u F1u Pb-localised<br />
BO3 translation vs Pb<br />
B-cation localised<br />
Pb-O bond stretching<br />
BO6 bending<br />
p-pol c-pol<br />
F 1u<br />
F 1u<br />
E g<br />
BO 6 stretching<br />
A 1g<br />
F 2g<br />
F 2u<br />
Pb-localised<br />
BO3 translation vs Pb<br />
B-localised<br />
Pb-O bond stretching<br />
BO6 bending<br />
BO6 str.<br />
bold: E i || [100]<br />
thin: E i || [110]<br />
F 2g<br />
PST<br />
PSN<br />
300-350 cm -1 (Pb-O stretching):<br />
correlated ferroic Pb-O species<br />
Raman-activity near 250 cm -1 :<br />
off-centre shifts of B-cations
PbSc 0.5Ta 0.5O 3 (PST) and Pb 0.78 Ba 0.22 Sc 0.5 Ta 0.5 O 3 (PBST) at AP<br />
Why those two compounds?<br />
PST<br />
PBST<br />
relaxor with long-range FE ordering at LT canonical relaxor
PST and PBST at HP<br />
Raman scattering, X-ray X ray diffraction and diffuse scattering<br />
AP - 9 GPa : • enhancement of the anisotropy in the Pb-O system<br />
• suppression of B-cation off-centre shifts<br />
PbSc 0.5Ta 0.5Ta0.5<br />
0.5 O3 new! new!<br />
Pb 0.78Ba 0.78Ba0.22Sc<br />
0.22Sc0.5Ta<br />
0.5Ta0.5<br />
0.5 O3 a sequence of local structural changes between 1.2 - 3.5 GPa<br />
reversible phase transition near 2.0 GPa<br />
(submitted for publication)<br />
new canonical relaxor! relaxor<br />
two types of Pb-O bonds revealed by pressure<br />
stiff octahedral distortions near the incorporated Ba cations<br />
responsible for the suppression of long-range FE ordering<br />
(to be submitted for publication)
Our research plan (next 12 months)<br />
HP Raman spectroscopy on PST and Ba-PST up to 15 GPa<br />
(an attempt to collect polarised spectra < 4 GPa)<br />
Analysis of the XRD data on<br />
PST and Ba-PST collected at DESY<br />
Pressure-induced structural transformations in PSN and Nb-doped PST<br />
(Raman scattering and XRD analysis)<br />
Ba-PSN and Ba-PST-PSN<br />
(Raman scattering)<br />
La-PST and La-PSN<br />
(Raman scattering)
Acknowledgements:<br />
Financial support by the DFG (MI 1127/2-1) 1127/2 1)<br />
Ross Angel, Jing Zhao, Jens Engel, Virginia Tech<br />
Alexandra Friedrich, Uni Frankfurt<br />
Clivia Hejny, Hejny,<br />
Uni Innsbruck<br />
Hans Ahsbahs, Ahsbahs,<br />
Uni Marburg<br />
Karsten Knorr, Knorr,<br />
Uni Kiel<br />
Leonid Dubrovinski,<br />
Dubrovinski,<br />
Uni Bayreuth<br />
Tiziana Boffa Ballaran, Ballaran,<br />
Uni Bayreuth<br />
Organisers and Lecturers of the Workshop in Bayreuth, 24.-26.04.2007<br />
24. 26.04.2007
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