Structural transformations in complex Structural transformations in ...

Fachbereich Geowissenschaften, Universität Hamburg
Structural transformations in complex
advanced ferroelectrics at high
pressures and temperatures
DFG Project MI 1127/2‐2
N. Waeselmann, B. Maier, R. Angel, M.
Gospodinov, U. Bismayer, B. Mihailova

Introduction
Outline
High‐pressure h experiments
Structural changes g in:
Relaxors at room temperature p up p to 30 GPa
Relaxors at high temperatures & pressures
09PZN01PTat 0.9PZN‐0.1PT at different temperatures
temperat res
0.9PZN‐0.1PT under high‐pressure
Conclusions
2

Perovskite CaTiO 3
Perovskite structure type
orthorhombic, Pnma cubic, Pm3m
www.fabreminerals.com
t R A R O
√2R B R O
0.78 < t < 1.05
bit = 0
Perovskite structure
cubic, Pm3m
bit = 1
3

Relaxors vs. normal Ferroelectrics
NNormal lF Ferroelectric l i
Relaxors
After Hirota et al. J. Phys. Soc. Jap. 2006
4

Model compounds & A‐site doping
Pb(Sc 0.5Ta 0.5)O 3 (PST) Pb(Sc 0.5Nb 0.5)O 3 (PSN)
Pm3m
Fm3m
lone pair electrons
5

chemically B‐site
disordered matrix
+
paraelectric
matrix
B‐site substitution disorder
chemically B‐site
ordered nanoregions
polar nanoregions
AFM ttopography h iin‐plane l PFM
PZN‐0.1PT average domain width: ~120 nm
Scholz et al. J. Appl. Phys. 2009
(1‐x)Pb(Zn 2+ 1/3Nb 5+ 2/3)O 3 – xPbTiO 3
6

Experimental setup
150 µm
7

Fm3m
Pressure medium and indicator
Alkali alkali halide halite salt salts
no Raman modes
ruby
Al 2O 3:Cr 3+
100 K 790 K
SrB O :Sm2+ SrB4O7:Sm negligible li ibl
100 K to 790 K
temperature
shift
8

p C2
PST up to 30 GPa
ure
pressu
pC1 pC2 = 5.5 GPa
p p2* 2 ~3.0 GPa
pC1 = 1.9 GPa
p1* = 1.2 GPa
1.2 GPa
3.0 GPa
F 2u
Pb‐O bond stretching
9

hk2
PST up to 30 GPa
ssure
pres
10

PbZn 1/3Nb 2/3O 3‐PbTiO 3 –temperature
tempeeraturee
11

PZN‐PT –temperature
12

PbB 2+ 1/3B 5+ 2/3O 3
Three possible permutations
(B2+ B5+ (B )
2+ 2/3B5+ 1/3)
PZN‐PT –temperature
Pb(B 2+ 2/3B 5+ 1/3) 0.5B 5+ 0.5O 3
13

Scholz et al. JAP 2009
PZN‐PT ‐ pressure
Single l crystal l X‐ray dff diffraction Raman scattering
p F-R p C1
p F-R
p C1
p F-R p C1
p F-R
p C1
14

Submitted/in preparation
In‐situ high‐temperature high‐pressure Raman
measurements t on PbS PbSc1/2 Nb Nb1/2 O O3 and d
PbSc1/2Ta1/2O3 .
High‐pressure Brillouin scattering of single‐
crystal PbSc05 0.5Ta05 0.5O 3
Doped high‐pressure Raman and XRD up to 30
GPa
A‐site doping
Local elastic field Smaller t Local electric field
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presssure
Conclusions: High pressure at RT
non‐polar rhombohedral non‐polar monoclinic / triclinic
a − a − a − a − b − b − , no Pb LRO
a − a − a − a + b − b − + anti‐polar Pb LRO
unequal BO 6 tilts around the cubic {100} axes on the local scale
relaxor‐cubic non‐polar rhombohedral state (a − a − a − )
decoupling of off‐centered Pb and B‐cations in PNRs
development of local anti‐polar order of Pb cations
development of quasi‐dynamical a ‐ a ‐ a ‐
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doubled
perovskite
structure
Conclusions: PZN‐PT
PbB 2+ 1/3B 5+ 2/3O 3‐PbTiO 3
giant giant piezoelectric piezoelectric effect effect
complex local structure multiphase domain state
17

Relaxors – frustrated ferrielectrics?
Anti‐ferroelectric Pb displacement
Off‐centered Pb atoms
polar displacement of B‐cation
Polar displacement of Pb‐BO 3
+ =
+ =
FE AFE
18

Publications (project MI 1127/2 1127/2‐2) 2)
B. Maier et al. (2010): A‐site doping induced renormalization phenomena in PbSc 0.5 Nb 0.5 O 3 under high pressure. Phys. Rev. B, 81,
174116/1‐8.
B. Maier et al (2010): Octahedral tilting in Pb‐based relaxor ferroelectrics at high pressure. Acta Cryst. B, 66, 280‐291.
B. Maier et al, High‐pressure powder neutron diffraction study on lead scandium niobate. J. Phys.: Condens. Matter, 23,
035902/1‐5.
A.‐M. Welsch et al. (2011): Transformation processes in relaxor ferroelectric PbSc 0.5 Ta 0.5 O 3 heavily doped with Nb and Sn.
Zeitschrift fuer Kristallographie, 226, 126‐137.
B. Maier et al. (2011): Effect of La doping on the ferroic order in Pb‐based relaxor ferroelectrics. Phys. Rev. B, 83, 134106/1‐12.
N. Waeselmann et al. (2011): Local structural phenomena in pure and Ru‐doped 0.9PbZn 1/3 Nb 2/3 O 3 ‐0.1PbTiO 3 near the
morphotropic phase boundary as revealed by Raman spectroscopy, Phys. Rev. B 83, 214104/1‐13.
B. Mihailova et al. (2011): The structural state of lead‐based relaxor ferroelectrics under pressure. IEEE Transactions on
Ultrasonics, Ferroelectrics and Frequency Control, 58, 1905 ‐ 1913. (invited contribution)
B. Maier, N. Waeselmann et al. (2011): The structural state of relaxor ferroelectrics PbSc 0.5 Ta 0.5 O 3 and PbSc 0.5 Nb 0.5 O 3 at high
pressures up to 30 GPa, Phys. Rev. B, 84, 174104/1‐11.
N. Waeselmann et al. (2012): Pressure induced structural transformations in pure and Ru‐doped 0.9PbZn 1/3 Nb 2/3 O 3 ‐0.1PbTiO 3
near the morphotropic phase boundary, Phys. Rev B, 85, 014106/1‐10.
submitted / in preparation:
N. Waeselmann et all. In‐situ high‐temperature high‐pressure Raman spectroscopy on lead‐based relaxor ferroelectrics
PbSc1/2Nb1/2O3 and PbSc1/2Ta1/2O3 .
M. Wehber, N. Waeselmann et al. High‐pressure Brillouin sctattering of single‐crystal PbSc0.5Ta0.5O3 relaxor ferroelectric.
B. Mihailova, N. Waeselmann et al. Chemically‐induced renormalization phenomena in Pb‐based relaxors under high pressure.
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Financial support by DFG MI1127/2‐2 20