Nuclear magnetic resonance of domain switching in ferroelectric rochelle sal

Casabella, P. A.

Oja, T.

English

NASA Technical Reports Server

1l " NMR S tudies  of Domain Switching 
t T. Oja and P. A. Casabella? 
I n t e r d i s c i p l i n a r y  Materials Research Center 
Rensselaer Polytechnic  I n s t i t u t e ,  Troy, New York 12181 
, 
ABSTRACT 
The N a 2 3  NMR sa te l l i t e  l i n e  spectrum i n  the  f e r r o e l e c t r i c  phase 
of Rochelle S a l t  is  used t o  obtain h y s t e r e s i s  loops and t o  i n v e s t i -  
g a t e  t h e  r e l a t i o n  between the  r a t e  of p o l a r i z a t i o n  reversal and t h e  
change of e x t e r n a l l y  appl ied  e l e c t r i c  f i e l d .  
https://ntrs.nasa.gov/search.jsp?R=19680015523 2020-03-12T10:28:45+00:00Z
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Severa l  i n v e s t i g a t o r s  have observed nuc lea r  magnetic resonance (NMR) 
quadrupole sa te l l i t e  l i n e s  s p l i t  i n t o  c l o s e l y  spaced doub le t s  i n  t h e  f e r ro -  
e lec t r ic  phases of Rochelle S a l t  (E) ', KI12P042 and KD2P04 3 .  The re la t ive 
i n t e n s i t y  of t he  two components of t h e  doublet  could b e  a l t e r e d  by applying 
an e x t e r n a l  d c  e lec t r ic  f i e l d  along t h e  f e r r o e l e c t r i c  axis1s2.  These exper- 
iments v e r i f i e d  t h a t  t h e  two components of t h e  doub le t  a rose  from n u c l e i  a t  
i d e n t i c a l  c r y s t a l l o g r a p h i c  s i t e s  but i n  oppos i t e ly  po la r i zed  domains. 
I n  t h i s  let ter t h e  f i r s t  domain switching experiment i n  a f e r r o e l e c t r i c  
c r y s t a l  u s ing  NMR sa te l l i t e  l i n e s  i n  reported4.  It  is  shown t h a t  t h e  N a 2 3  
(I = 3/2)  NMR sa te l l i t e  l i n e  spectrum i n  t h e  f e r r o e l e c t r i c  phase of RS can 
be u t i l i z e d  t o  o b t a i n  h y s t e r e s i s  loops. Hys te re s i s  loops observed i n  t h i s  
manner are d r a s t i c a l l y  d i f f e r e n t  from t h e  convent ional  h y s t e r e s i s  loops 
("normal loops") obtained by t h e  usual  Sawyer-Tower b r i d g e  method5. 
f u r t h e r  demonstrated t h a t  t h e  NMR method can a l s o  b e  used t o  perform dynamic 
It is 
switching experiments t o  i n v e s t i g a t e  t h e  dependence of t h e  rate of po la r i za -  
t i o n  reversal on t h e  change of applied electric f i e l d .  
Rochelle S a l t  is  f e r r o e l e c t r i c  only between -18°C<T<+240C and is  s t r u c -  
t u r a l l y  very complex6. 
p l e t e d .  N a 2  NMR i n v e s t i g a t i o n s 1  9 have s u c c e s s f u l l y  v e r i f i e d  t h e  
proposed8 i o n i c  d i p o l e  displacements r e spons ib l e  f o r  f e r r o e l e c t r i c i t y  i n  
RS. 
d i r e c t i o n s  toge the r  w i t h  t h e  symmetry operat ions f o r  t h e  non- fe r roe lec t r i c ,  
orthorhombic phase (T>+24'C) .  
s i t e s  and t h e  arrows are the  major f e r r o e l e c t r i c  d i p o l e s .  
The d e t a i l e d  s t r u c t u r a l  a n a l y s i s  has  n o t  been com- 
Figure 1 shows two s impl i f i ed  u n i t  cells  of RS po la r i zed  i n  opposi te  
The open circles r e p r e s e n t  t h e  f o u r  Na23 
The f e r r o e l e c t r i c  domain s t r u c t u r e  of RS is, neve r the l e s s ,  r e l a t i v e l y  
s imple.  Domains are s l a b s  p a r a l l e l  t o  ab plane (b-domains) o r  s l a b s  
3 
p a r a l l e l  t o  ac plane (c-domains) of p a r a l l e l  o r  a n t i - p a r a l l e l  p o l a r i z a t i o n  
along t h e  a-axis'. 
dynamics of b- and c-domains. 
No s i g n i f i c a n t  d i f f e r e n c e s  have been de tec ted  i n  t h e  
The Na23 NMR spectum i n  the  higher temperature non-f e r r o e l e c t r i c  phase 
has  e i g h t  quadrupole s a t e l l i t e  l i n e s ;  one p a i r  f o r  each of t h e  f o u r  phys- 
i c a l l y  inequ iva len t  N a 2 3  s i tes  pe r  u n i t  cell.  Upon cool ing  i n t o  the  f e r r o -  
e l e c t r i c  phase, each sa te l l i t e  w a s  observed t o  s h i f t  frequency and s p l i t  
i n t o  a c l o s e l y  spaced doublet ,  w i t h  t h e  double t  spacing dependent on the  
o r i e n t a t i o n  of t he  c r y s t a l .  An e x t e r n a l  d c  e l e c t r i c  f i e l d  i n  the  d i r e c t i o n  
of the f e r r o e l e c t r i c  a-axis removed one member of each double t ,  t h e  remain- 
i ng  member growing t o  twice i t s  o r i g i n a l  i n t e n s i t y .  Upon r eve r s ing  the  
electric f i e l d  t h e  l i n e s  which had o r i g i n a l l y  disappeared, reappeared, and 
the  o t h e r  member of each double t  had now disappeared v e r i f y i n g  t h a t  t h e  
s p l i t t i n g  w a s  indeed caused by f e r r o e l e c t r i c  domains. No evidence of domains 
is  p r e s e n t  i f  one of t he  c r y s t a l  axes is  perpendicular  t o  H 
po la r i zed  domains are twins of each o t h e r  and would go i n t o  each o t h e r  under 
t h e  two orthorhombic symmetry ope ra t ions  thus  l ead ing  t o  i d e n t i c a l  NMR 
s i n c e  oppos i te ly  
0 
spectra. 
The r e s u l t s  presented h e r e  were obtained on c r y s t a l  p l a t e s  ( th i ckness  - 
.6 cm) whose z axes  were t i l t e d  about 8' from pe rpend icu la r i ty  wi th  H 
experiments  were performed a t  +3'C us ing  a convent ional  P.K.W. spectrometer  
w i th  app l i ed  vo l t ages  suppl ied  by b a t t e r i e s .  
The 
0 .  
A t y p i c a l  h y s t e r e s i s  loop, 
shown i n  Fig.  2, was obtained by scanning the  spectrometer  frequency over 
bo th  members of a s u i t a b l e  doublet  and p l o t t i n g  the  peak-to-peak amplitude 
of one member of t'he double t  using t h e  o the r  member as amplitude r e fe rence  
I 
s i n c e  it can be assumed t h a t  t h e  sum of t h e  two amplitudes is  a cons tan t .  
4 
T h s  ap?i ied v o l t z g e  was maintained ac ross  t h e  crystal  throughout t h e  experi-  
nea t  and rhe spectrometer w a s  scanned through the  doublet  each time t h e  
' v o i c a g e  was changed. The t r a c i n g  out of t h e  complete loop  took up t o  12 
hours and w i l l  be c a l l e d  a "quasi-s ta t ic"  loop. 
E-axis i s  probably due to  a small amount of i n t e r n a l  bias .5  
The s l i g h t  s h i f t  a long t h e  
Quas i - s t a t i c  loops obtained by NElR are very r ec t angu la r  w i t h  a v e r y  
low coe rc ive  f i e l d  of about 25 V/cm. The "normal" loops obtained a t  +3"C 
with s i n e  wave f i e l d  of 50 c/sec or  h ighe r  have coe rc ive  f i e l d s  of about 
150 V / c m l 0  9 l 1  ate. are considera3ly more rounded. 
I 
The dynamic domain switching experiments were performed by f i r s t  polar- 
i z i n g  the  c r y s t a l  t o  t he  point  D i n  Fig.  2, lowering t h e  f i e l d  t o  arrive a t  
p o i n t  E and then switching from E t o  E '  (AEl - 9.0 V/cm) o r  to  D' 
(AE2 = 52 V/cm) .  
t h e  spectrometer w a s  d r iven  up t o  t h e  d e r i v a t i v e  peak of t h i s  l i n e  (po in t  A 
A t  po in t  E only one sa te l l i t e  of t h e  p a i r  i s  p r e s e n t  and 
Fig .  3) and t h e  frequency d r i v e  was s h u t  o f f .  Af t e r  a few minutes t h e  elec- 
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t r i c  f i e l d  w a s  switched (at  t h e  point  i nd ica t ed  by t h e  ver t ica l  arrow) by 
t h e  amount AE2, and t h e  s a t e l l i t e  on which t h e  spectrometer w a s  s i t t i n g  
I 
decayed r a p i d l y  a t  the  expense of t h e  o t h e r  s a t e l l i t e  (not  shown) which w a s  
b u i l d i n g  up i n  amplitude. 
Fig.  3) i n  about 5 sec. 
Tne spectrometer reached t h e  base - l ine  ( p o i n t  B 
Th i s  decay time is e n t i r e l y  due t o  t h e  t i m e  c o n s t a n t  
a s s o c i a t e d  w i t h  t h e  spectrometer.  
D' ( t h e  c r y s t a l  being returned t o  p o i n t  E along t h e  bottom p o r t i o n  of t h e  
loop)  are shown a t  top l e f t  of Fig. 3. 
s t a b i l i t y  of t h e  spectrometer and magnet which were completely free-running. 
The bottom p o r t i o n  of Fig. 3 shows a t y p i c a l  trace of a switch from E t o  E' 
(AEl - 9.0 V) ( t h e  a c t u a l  switching took p l ace  a t  t h e  p o i n t  i n d i c a t e d  by 
Four c y c l e s  of switching from p o i n t  E t o  
Th i s  trace a t tes ts  t o  t h e  long term 
I . 
5 
t h e  v e r t i c a l  arrow). The po la r i za t ion  r e v e r s a l  i n  t h i s  case took about 15 
minutes t o  complete. 
Previous p o l a r i z a t i o n  r e v e r s a l  experiments i n  RS were performed by two 
very d i f f e r e n t  techniques y i e l d i n g  a l s o  two very  d i f f e r e n t  r e s u l t s .  The 
o p t i c a l  experiments of Nakamurn, l2 using a p o l a r i z i n g  l i g h t  microscope, 
shoved t h a t  t h e  p o l a r i z a t i o n  r eve r sa l  i n  RS took p l ace  v i a  slow sideways 
expansion of b- and c-domain wa l l s ,  t h a t  t h e r e  e x i s t s  a " c r i t i c a l "  o r  
" threshold" f i e l d ,  Eo, below which no reversal can take  place,  and t h a t  once 
E w a s  exceeded the  swi tch ing  time T w a s  given by 1 / ~  a(E-E ). 
r e s u l t s  a domain w a l l  mobi l i ty ,  p = 1.36 x 
mined. 
From these  
0 0 
cm2 V'I sec-l, was de t e r -  
The NMR r e s u l t s  presented here  are i n  very  good q u a l i t a t i v e  agreement 
wi th  Nakamura's r e s u l t s .  Furthermore, t h e  NMR r e s u l t s  are very  reproducib le  
and are a bulk  measurement. The lack of q u a n t i t a t i v e  agreement, e s p e c i a l l y  
.with regard t o  d i f f e r e n c e s  i n  E between the  two experiments is  n o t  s e r i o u s  
and can be  a t t r i b u t e d  t o  d i f f e rences  i n  c r y s t a l  th icknesses  and t o  d i f f e r -  
ences  i n  the  temperatures between t h e  two experiments.  
experiments g ive  r e s u l t s  i n  one focal p lane  only which might no t  b e  repre-  
s e n t a t i v e  of t he  bulk  crystal .  
0 
Also the  o p t i c a l  
Vas t ly  d i f f e r e n t  r e s u l t s  were obtained by Wiederl  who i n v e s t i g a t e d  
p o l a r i z a t i o n  reversal by applying very  f a s t  rise-time p u l s e s  of a l t e r n a t i n g  
p o l a r i t y  t o  t h e  c r y s t a l .  
of 10 V / c m  and domain w a l l  mob i l i t i e s  were ca l cu la t ed  t o  be 110 cm2 V'l 
sec'l. 
No "critical" f i e l d  w a s  observed down t o  f i e l d s  
I n  t h e  case  of f a s t  puls ing experiments t he  p o l a r i z a t i o n  r e v e r s a l  
is be l ieved  t o  be  by .nuc lea t ion  and w a l l  propagat ion i n  t h e  f e r r o e l e c t r i c  
axis  d i r e c t i o n  which is evidently a much f a s t e r  process  than the sfbc.-,.zy= 
6 
expansion of b- and c-domain w a l l s .  I t  would seem t h e r e f o r e ,  t h a t  r e v e r s i n g  
t h e  p o l a r i z a t i o n  by ?leans of a s i n e  wave f i e l d ,  as i n  t h e  case when obtain-  
i n g  h y s t e r e s i s  loops by t h e  Sawyer-Tower b r i d g e  method l i es  somewhere be- 
tween t h e  two extremes of "quasi-s ta t ic"  switching and pulsed switching and 
should be descr ibed by a s u i t a b l e  mixture of bo th  processes.  
of change of appl ied f i e l d  ( v i r t u a l l y  zero f o r  q u a s i - s t a t i c  switching and 
extremely high f o r  pulsed switching) seems t o  determine which process  pre- 
dominates. 
Hence t h e  rate 
I n  conclusion, i t  is seen t h a t  t h e  NMR r e s u l t s  on p o l a r i z a t i o n  rever- 
sa l  i n  RS p a r a l l e l  t h e  r e s u l t s  of the o p t i c a l  work of Nakamura and t h a t  t h e  
NMR method gives  r e s u l t s  on p o l a r i z a t i o n  r e v e r s a l  via t h e  slow sideways 
motion of b- and c-domain walls. 
i n  th i s  le t ter  should a l s o  prove use fu l  i n  t h e  i n v e s t i g a t i o n s  of quasi-  
s t a t i c  p o l a r i z a t i o n  reversal  i n  many o t h e r  f e r r o e l e c t r i c s  such as guanidine 
aluminum s u l f a t e  hexahydrate (GASH) and r e l a t e d  compounds, deu te ra t ed  tri- 
g l y c i n e  s u l f a t e  (DTGS), and isomorphs, etc. i n  which domain s t r u c t u r e s  can- 
n o t  be observed by t h e  p o l a r i z i n g  l i g h t  microscope method without  s t r a i n i n g  
t h e  c r y s t a l s 5 ,  o r  i n  KH2S04, KDzSOI, and isomorphs i n  which t h e  f e r r o e l e c t r i c  
phase appears only a t  r e l a t i v e l y  low temperatures thus p re sen t ing  formidable 
experimental  problems f o r  microscope work. 
Furthermore, t h e  NMR methods discussed 
FOOTNOTES 
* 
This  work w a s  supported by the  United S t a t e  Atomic Energy Commission 
and t h e  Nat iona l  Aeronautics and Space Adminis t ra t ion.  It  is based 
upon the  d i s s e r t a t i o n  submitted by T. Oja i n  p a r t i a l  f u l f i l l m e n t  of 
t h e  requirements f o r  t he  Ph.D. degree a t  Rensselaer  Poly technic  I n s t i t u t e .  
TPresent  address:  Department of Physics,  Brown Univers i ty ,  Providence, 
Rhode I s l and  02912. 
?Department of Phys ics  and Astronomy, 
1. N. C. Miller and P, A. Casabella,  Phys. Rev. 152, 228 (1966). -
2. Y .  Tsutsumi et. a l ,  J. Phys. SOC. Japan 24, 429 (1968). -
3. J. L. Bjorkstam, Phys. Rev. 153, 599 (1967). -
4. R. C. Duvarney and R,  P. Kohin, Phys. Rev. Letters 20, 259 (1968). 
( F i r s t  observed domain switching i n  i r r a d i a t e d  f e r r o e l e c t r i c  KH~POL, 
by ESR). 
For  a comprehensive review of f e r r o e l e c t r i c  p r o p e r t i e s  see E. Fatuzzo 5. 
and W. J. Merz, F e r r o e l e c t r i c i t y  (North-Holland Publ i sh ing  Company, 
Amsterdam, The Nether lands,  1967) and F. Jona and E. Shirane,  Ferro- 
e l e c t r i c  C r y s t a l s  (The MacMillan Company, New York, 1962). 
6 .  A. R. Ubbeleohde and I. Woodward, Proc. Roy. SOC. (London) 179, 399 
(1942). 
1435 (1954). 
R. Bl inc ,  J. Petkovesek, and I. Zupanicic,  Phys. Rev. - 136, 1684 (1964). 
B. C. F razer ,  J. Phys. SOC.  Japan, - 1 7 ,  Suppl. B-11 (1961). 
T. Mi tsu i  and J. Furv ich i ,  Phys. Rev. - 90, 193 (1953). 
10. J. Hablii tzel ,  Helv. Phys. Acta - 12, 489 (1939). 
11. H. H. Wieder, Phys. Rev. - 110, 29 (1958). 
12. T. Nakamra, J. Phys. SOC. Japan l2, 477 (1957). 
B. C. Frazer ,  M, McKeown, and R. Pepinsky, Phys. Rev. 94, 
7.  
8. 
9. 
7 
8 
FIGURE CAPTIONS 
Fig. 1. Pro jec t ion  on the  (001) plane of two s i m p l i f i e d  u n i t  cel ls  of 
Rochelle Sa l t  polar ized i n  oppos i t e  d i r e c t i o n s .  The open circles 
are t h e  sites. The small arrows are t h e  major f e r r o e l e c t r i c  
d ipo le s .  The symmetry operat ions f o r  t he  upper non- fe r roe lec t r i c  
phase (orthorhombic P21212) are shown. 
phase t h e  c r y s t a l  i s  monoclinic wi th  symmetry P21 along a. 
I n  t h e  f e r r o e l e c t r i c  
S i t e s  
A and B have s l i g h t l y  d i f f e r e n t  quadrupole coupl ing cons t an t s  and 
asymmetry parameters (see Ref. 1 and 7 ) .  
Fig. 2. A h y s t e r e s i s  loop obtained by NMR. The re la t ive amplitude ( i n  %) 
of one satel l i te  of t h e  doublet  as a func t ion  of e x t e r n a l l y  
appl ied electric f i e l d .  The coe rc ive  f i e l d  i s  de f ined  as h a l f  
t h e  loop width. P o i n t s  D, E ,  E' and D' are r e f e r r e d  t o  i n  t h e  
t e x t  and are concerned with t h e  dynamic switching experiment. 
Fig. 3. Resul ts  of t h e  dynamic domain switching experiment. Note t h a t  
t i m e  i nc reases  from r i g h t  t o  l e f t  i n  t h i s  f i g u r e .  
shows a t y p i c a l  sa te l l i t e  l i n e  from which t h e  switching w a s  car- 
r i e d  out.  Top l e f t  shows repeated switching (AE2 = 52 V/cm) from 
t h e  peak of t h e  d e r i v a t i v e  curve (A). Switching occurs a t  p o i n t s  
i nd ica t ed  by vertical  arrows and a f t e r  each switch t h e  c r y s t a l  is 
r e tu rned  t o  t h e  o r i g i n a l  s t a r t i n g  p l a c e  ( p o i n t  E i n  Fig.  2) v ia  
t h e  bottom p o r t i o n  of t he  h y s t e r e s i s  loop. A t  p o i n t  B t h e  spectro-  
meter h a s  r e tu rned  t o  the  base l i n e .  Bottom por t ion  of t h i s  f i g u r e  
shows t h e  i d e n t i c a l  experiment b u t  t h i s  t i m e  t h e  f i e l d  h a s  been 
switched by t h e  amount AE1 = 9.0 V / c m  ( t h e  a c t u a l  switching t ak ing  
p l ace  a t  t h e  ver t ica l  arrow). 
of t he  spectrometer i n  t h i s  case took about 15 minutes. 
Top r i g h t  
The r e t u r n  to base  l i n e  (po in t  bj 
+-------- T-- I I ' i -  
I I '  1 c-1 I 
I +-+---- 7-- * L 
' .  
% LINE AMPLITUDE 
D 
X 
* 
I I I 
0 
X 
Ioox-cTx- 
.90 
.80 
-70 
- 60 
50 
I 
20 
.40 
-30 
- 20 
40 
E(voIts/crn) 
4 0  60 
Fig. 2 
a 
t 
m 


NMR studies of domain switching in ferroelectric rochelle salt

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