Transcript Własności ferroelektryczne kryształów SBN

Dynamika struktury domenowej w relaksorowych kryształach ferroelektrycznych
1. Niobian strontowo-barowy Sr0.61Ba0.39Nb2O6 (SBN) Tc=353K 4/mmm→4mm relaksor
0.25 < x < 0.75
2. Siarczan trójglicyny (NH2CH2COOH)3H2SO4 (TGS) Tc=322K P21/m→P21 kryształ jednorodny
3. Kompleks kwasu tellurowego z fosforanami amonu
Te(OH)6·2NH4H2PO4·(NH4)2HPO4 (TAAP) Tc=321K P2/m→Pm kryształ niejednorodny
Katarzyna Matyjasek
Teoria Landaua – Ginzburga – Devonshire’a.
Gęstość energii swobodnej G można przybliżyć,
używając następującego szeregu potęgowego polaryzacji P.
Curie–Weiss law
(a) Double well potential and ferroelectric unit cell
(b) Random field (asymmetric) disorder in a ferroelectric material
1 – defects – free material
2 – a weak random field
3 – non-polar phase
dN 1
b)
~ ~ exp(1 / E )
dt tn
1
c)Vt ~ ~ E n
tt
1
d )Vb ~ ~ exp( 2 / E )
tb
ExamplesP of the hysteresis loops measured with a bridge method for a uniform (TGS),
non-uniform (TAAP) and relaxor (SBN) ferroelectric crystals
P
2,5
2,0
2
P(t) [C/cm ]
1,5
4,25 kV/m
4,5 kV/m
4,75 kV/m
4,95 kV/m
5,25 kV/m
5,5 kV/m
5,75 kV/m
6 kV/m
6,2 kV/m
1,0
0,5
E
0,0
0
2
4
6
8
t [ms]
Tryglicine sulphate (TGS), E=14kV/m,
EC=7.5kV/m, P=2.13µC/cm2
1,0
2
PS [C/cm ]
7
0,9
P
0,8
0,7
P
6
0,5
0,4
0,3
0,2
Gladkii fitting
5
4
4
3
3
E
2
0,1
0,0
-0,1
-0,05
1 - E=2kV/cm, k=0.88
2 - E=2.5kV/cm, k=0.96
3 - E=3kV/cm, k=0.68
4 - E=3.5kV/cm, k=0.23
5 - E=4kV/cm, k=0.12
5
P, C/cm2
0,6
50 kV/m
75 kV/m
100 kV/m
150 kV/m
175 kV/m
250 kV/m
2
1
1
0,00
0,05
0,10
0,15
0,20
t [ms]
Telluric acid ammonium phosphate (TAAP), E=480kV/m, EC=187kV/m, P=1.16µC/cm2,
Eb=225kV/m
E
0,25
0
0
2
4
6
8
10
time, ms
Strontium barium niobate (SBN), E=680kV/m, EC=360kV/m, P=17.5µC/cm2
TAAP
E=2.2kV/cm
E=0
The domain pattern evolution observed in TGS crystal sample during switching process in negative
electric field of 0.4 kVcm−1 (applied at t = 0). Time fromthemoment of applying E in [s] (a) 0.2; (b) 0.4;
(c) 0.8; (d) 1.8; Distribution of domains in: negative E in [kVcm−1] (e) 0.5; (f ) 0.7; positive E (g) 0.4; (h) 0.7.
Domain patten evolution observed in SBN crystal sample during switching in the positive electric
field of 2.8 kVcm−1. (a) — initial single domain state. Time from the moment of applying E in [s];
(b) — 0.2; (c) — 0.4; (d) — 0.6; (e) — 0.8; (f ) — 1; (g) — 3.8; (h) — shows the domain pattern obtained after
applying the negative electric field of 2.8 kVcm−1. Ferroelectrics 2013; K. Matyjasek, M. Orłowski
61
TGS
TAAP
A (110) plane through the PSN simulation box representing the projected
local field (arbitrary regions (approximately circular) have small approximately
homogeneous units) at each Pb site in the plane. Chemically
ordered fields, and chemically disordered regions have larger
more varied and disordered local fields. After [Tinte, Burton, Cockayne
and Waghmare: Phys. Rev. Lett. 97, 137601 (2006)].
Molecular Dynamics Simulations of relaxors
Takeshi Nishimatsu 2010
Niobian strontowo-barowy Sr0.61Ba0.39Nb2O6 (SBN) Tc=353K 4/mmm→4mm relaxor
0.25 < x < 0.75
295K
354K
SrxBa1-xNb2O6
(x=0.5)
- disordered Ba – Sr site
- site preferred by Sr
- alternative oxygen atom site
in niobium oxygen octahedra
SBN 70
SBN 33
SBN26
+0.6
1<E<1.5kV/cm
SBN70
SBN 26
-0.6kV/cm
SBN26
1.3
1.4
1.5kV/cm
1kV/cm, t=8s
SBN 61 + Cr
320K
330K
E=2.4kV/cm
E=-2.4kV/cm
E=2.4kV/cm
K Matyjasek, S M Kaczmarek, L I Ivleva Ferroelectrics 2012
340K
2,8 kV/cm
2,5 kV/cm
Ni (0,01 wt.%) 1,1 kV/cm Ni(0,5 wt.%)