Chaudhuri, B K

Kundu, S K

Okabe, E

IACS Institutional Repository

uluinJ. Fhys. 75A (2), 109-111 (2001)U P  A— an international )ournalRapid CommmdcatlwrObservation of successive phase transitions in ferroelectric liquid crystal (CS-1013) from dielectric measurements pnd a pseudospin type model for studying ferro and antiferroelectric behaviourS K  K u n d u , E  O k a b e ',  B K  C h a u d h u il*  a n d  W  H aase* *i'Solid Stale Physics Department. Indian Association IFoi ihc Cultivation ot Sucikc Jadavpui, Calcutta-700 India\Specialty Chemicals Research Center, Chisso Petrochemical Corporation. 5-1 Goikaigan Ichihara Chiba 290-S551, Japan **Department of Physical Chemistry, Technioil University Darmstadt,Petersen strassc-20. Darmstadt. GermanyE-mail sspbkct^i’mahendia lacs res in Rfietvcd 13 November 20()(). tm epted 23 Novemhei 2000Ahslract From dielectric measurements, we have shown the appearance ol successive pha.se transitions in a tenoelecliic liquid crystal CS-1013(UiwiTM crystalline and isotropic pha.ses, we observed successive phase transitions viz Cr • -  55 ’ SniC*‘ - 63 C - SmA 7()'C'-N* 80 C-l.so Both (ii'ldstone mode (GM) and Soft mode (SM) arc ob.served in the SniC* fihase A theoretical pseudospin type model has been suggested foi studying ferro mJ aanlerioelectric phase transitions in liquid crystalsKeywords Liquid crysial. tcrrocleclricity, Goldstonc and soil model‘V('S No. 77 90. 4k^'liasc tran s itio n  in  c ry s ta ll in e  rc r ro e lc c tr ic  m a te r ia l is a v a s tly  ^uidiecl licld o f  in te re s t  11 ]. B u t p h a se  tra n s it io n  in  fe r ro e le c tr ic  licjuu! crystal is a  m o s t re c e n t d is c o v e ry  w h en  4 -  (1 ‘m e lh y lh cp ty  li> x v c a ih o n y l)  p h e n y l  4 ’- o c t y l b i p h e n y l - 4 - c a r b o x y l a t c  'M H PO B C ) w a s  fo u n d  to  b e  th e  firs t fe rro e le c tr ic  liq u id  c ry s ta l l- l  A f te r  th i s  d i s c o v e r y ,  m a n y  c h i r a l  c o m p o u n d s  w ith  mcsophascs viz. fe rro e lec tric  (F H )-S m C * , an tifcrrtx jlcctric  (A F E )- f e r r ic lc c t r ic  (FE FA -Sm C .^, Sm^^C* e tc . h a v e  b e e n  discovered by  e le c tro  o p tic  [3 ,4 ] , sw itc h in g  [ 2 , 5 , 6 |,  p y ro e lec tr ic  and o th e r m e a s u r in g  te c h n iq u e s . H o w e v e r , n o n e  o f  th e se  lechniqucs is  s e lf -s u ff ic ie n t to  p ro v id e  d e ta i le d  in fo rm a tio n  o f  (e r ro e lc c lr ic  p h a s e  tr a n s i t io n ,  m o le c u la r  d y n a m ic s  etc. tem perature an d  f re q u e n c y -d e p e n d e n t d ie le c tr ic  p e rm ittiv ity  lo s s  d a ta  p r o v i d e  im p o r t a n t  in f o r m a t io n  a b o u t  th e  ''Uccessive p h a se  tr a n s it io n s  a n d  m o le c u la r  d y n a m ic s  in  liq u id  crystals.In the p re s e n t c o m m u n ic a t io n , w e  re p o r t  th e  d if fe re n t p h a se  t^^iinsitions o c c u rr in g  b e tw e e n  th e  c ry s ta ll in e  a n d  th e  iso tro p ic  o f  a  ty p i c a l  f e r r o e l e c t r i c  l i q u id  c r y s ta l  F L C  viz.’^»nesponding AuthorC S-101.3  u s in g  d ie le c tr ic  sp e c tro sc o p ic  tech n iq u e . T h e  sam p le  w as  p re p a re d  by  C h is s o  P e tro c h e m ic a l C o rp o ra t io n , Ja p a n . D ic lc c ln c  c o n s ta n ts  (b o th  rea l an d  th e  im ag in a ry  p a rts ) w ere  m e a s u re d  by  a c o m p u te r  c o n tro l le d  H P  4 I 9 2 A  im p e d a n c e  an a ly /.c r  h a v in g  m e a su rin g  lie q u c n c y  ran g e  b e tw een  5 H /  and  13 M H z. T h e  te m p e ra tu re  w as c o n tro lle d  (w ith  an acc u ra c y  ol ± 0 .1*^0  by an  E u ro th e rm  tem p era tu re  c o n tro lle r  I’he tem p era tu re  range  o f  o u r investigation  w as b etw een  29-K2‘’C . O u r experim ental se t-u p  is s im ila r  to  th a t d e sc r ib e d  e ls e w h e re  [8, 9 ]. S p u tte red  g o ld  p la te d  e le c tro d e s  w e re  u se d  to  m e a su re  th e  d ie le c tr ic  c o n s ta n t o f  th e  F L C  la y e r  o f  th ic k n e ss  ~ 15 p m . T h e  l^LC filled  ce ll w as p re p a re d  by  c a p illa ry  a c tio n  m e th o d  in  an iso tro p ic  pha,sc. S tab ilized  low  freq u en cy  ac field  ( -  1.67 k V /cm ) w as used  fo r b e tte r  m o le c u la r  a lig n m e n t in th is  F L C  .sam ple. T h e  d iffe ren t p h a se s  o f  S C - 1013 s tu d ie d  by  o th e r  m e th o d s  [ I 0 |  a rc  sh o w n  b e lo wU .K. 6 3 T  7 0 C  8 0 CC rysta lline---------- S m C * -------- S m A -----------N*^--------- Iso (1)S o m e  im p o r ta n t p a ra m e te r s  o f  th e  liq u id  c ry s ta l  u n d e r  in v e s tig a tio n  a rc  sh o w n  in T ab le  1.n o 5 K Kumln, E  Okahe. B K Chaudhuri and  W  H aaseTable 1. Some imporianl parameters of the terroelectnc liquid crystal CS lOL^Spontaneous polarization (Ps) 25‘CTilt angle {$ ) 25 'CHelical pitch in N* phase - T^"Helical pitch in SmC* phase 25"CResponse lime ( r )Rotational Viscosity Optical anisoiiopy (An)2.S”C,H = ± lOV/pm25'C15 OnCcm - 26 deg 38 pm 6 pm 73*) psec1282 mPa s25'C. X = 546 nm 0 121) means N**SiiiA just above transition temperature2) ^0 ~ t//,sm^ 0F ig u re  I s h o w s  th e  te m p e ra tu re  d e p e n d e n t  d ie le c tr ic  lo s s  {t'/') fa c to r  a t tw o  d if f e re n t  f ix e d  f r e q u e n c ie s  ( I  a n d  10 k H z ). D if f e re n t  p h a s e  t r a n s i t io n s  d e s c r ib e d  b y  e q . (1 )  a re  c le a r lyFif(ure 1. Temperature-dependent dielectric loss (r") of feiroeleciric CSIO-13 .showing different phaseso b s e rv e d  fro m  th is  F ig u re . T h e  S m A -S m C *  p h a s e  transition a p p e a rs  to  be  f irs t o rd e r  in  n a tu re . T e m p e r a tu re  d ep en d en ce  oi d ie le c tr ic  p e rm it t iv i ty  (e/) s h o w n  in  F ig u re  2 a ls o  ind ica tes (he p re s e n c e  o f  d i f f e re n t  p h a s e s  in  SC> 1 0 13.It is  w e ll k n o w n  th a t  in  p la n a r  a l ig n m e n t ,  th e  dicicuric p e rm ittiv ity  d u e  to  G o ld s lo n c  m o d e  [ 8, 1 1 ] is d o m in a te d  in Smc^ p h a s e  w h ic h  a p p e a rs  d u e  to  th e  p h a s e  f lu c tu a t io n s  in  tilt angle o f  th e  m o le c u le s . T h e  o th e r  e le c tr ic  p e rm it t iv i ty  contributions a re  d u e  to  so f t m o d e  f 12] (c a u s e d  b y  a m p litu d e  f lu c tu a tio n  m tih a n g le ) , d o m a in  m o d e  f l 3 ]  a n d  u n w in d in g  m o d e  f l 4 ]  (earlier th e o r e t ic a l ly  p re d ic te d ) .  T h e s e  m o d e s  a re  g e n e ra l ly  observed b y  s u p p r e s s in g  th e  G o ld s to n c  m o d e  in  wSmC* p h a se . In the p re s e n t .sam ple, th e  d ie le c tr ic  p e rm it tiv ity  d u e  to  G o ld sto n c  mutk is d o m in a te d  in  th e  S m C *  p h a se . H o w e v e r , so f t m o d e  is also o b s e rv e d  n e a r  th e  S m A -S m C *  tr a n s i t io n  re g io n , a s  obsciufl f ro m  F ig u re  3. It is in te re s t in g  to  n o te  th a t o n e  a lso  observes ( f ro m  F ig u re  3 ) a  n e w  m o le c u la r  m o d e  a ro u n d  7 ()k H z  Iliis  ne\K m o d e  is  c o n s id e re d  to  b e  d u e  to  th e  r e - o n c n la t io n  o f  the lun ’^ h e lic a l a x is . S im ila r  c u rv e s  h a v e  a ls o  b e e n  o b ta in e d  a t diileict.! t e m p e r a tu r e s  a n d  f r e q u e n c ie s  s h o w in g  s e v e r a l  intcresim ;: f e a tu re s  in  th is  F L C  w h ic h  w o u ld  be  p u b lis h e d  e ls e w h e reFigure 2. Temperature-dependent dielectric permittivity (real part £')o f fe rro c lecn ic  C S-1013 at tw o d ifferen t tem pera tu res.Figure 3. Frequency dependence of the iinaginaiy pari of diflcciiK constant ie") m ferroelectric SmC*^  phase at different fixed lempcruuia^W c f in d  th a t th e  c ry s ta l l in e  to  fe r ro e le c tr ic  (S m C * )  phase tr a n s i t io n  c a n  b e  w e ll d e s c r ib e d  by  a  p s e u d o s p in  Hamiltonian o f  th e  fo rmA/ =  EEaf - -UE{cTj f -BZ{cT ; ) 'H e re , th e  p s e u d o s p in  v a r ia b le  <j (w ith  , and <rc o m p o n e n ts )  is a s s o c ia te d  w ith  th e  lo n g  a x is  o f  th e  m o lecu le  ^ is th e  e le c tr ic  f ie ld  ( E ) - d e p e n d e n l  d ip o le  m o m e n t,  U  is ih*' m a g n i tu d e  o f  th e  u n ia x ia l i ty  p a r a m e te r  re p r e s e n t in g  single m o le c u la r  a n iso tro p y  in  th e  z  d ire c tio n  o f  p o la r iz a tio n  (a  incasuic o f  th e  m a g n i tu d e  o f  p i tc h ) ,  B  is  th e  m a g n i tu d e  o f  th e  biaxialib p a r a m e te r  re p r e s e n tin g  th e  m o le c u la r  a n is o tro p y  transverse  i» th e  z -d ire c t io n  (a  m e a s u re  o f  th e  t i l t  a n g le  9 ) an d  7,  ^ O O ioi fe i ro e le c ir ic  t r a n s i t io n  a n d  <  0  fo r  a n ti f e r ro e le c tr ic  transition)Observation of successive phase transitions in ferroelectric liquid crystal etc IIihc dTc’Clivc exchange in te rac tio n  betw een  the d ipo les ipscuilospin). J is also a measure o f the interaction strength lici\ucn B and U (i.e. pitch and Q ) at sites i and j. All the [uranH'tcrs U. B, and J undergo thermodynamic lluctuaiions Kilmii: with tilt angle and pitch) and are responsible for different iiicsophasc transitions in the liquid crystals. Though this model H;iniilionian |cq. (2)] is similar to that of Devil's staircase model ;j.,ed by Yamashita and M iyazima [15], our derivation of the model and physical significance o f the model parameters arc .iuiie diflerent from those used by them. Detailed calculations iho iiansition temperature, spontaneous polarization etc. using iliiv iniidel jcq. (2)| will be published elsewhere.\rknowledgmentOne ol ihe authors (BKC) is grateful to the AvH Foundation for providing the HP frequency analyser and the tem perature uiiurollcr as gift. The author SKK is also grateful to the Council oi Sacntific & Industrial Research (India) for providing a k'limvship to work in this project.Rtfircnccs|1! M E Lines and A M Glass P m u i p l c s  a n d  A p p l n a t w n s  of F e n o e l e f t i i c s  a n d  A n t i f e r i n e l e u m s  (Oxford . Clarendon) (1977)12] A D L Chandani, T Hagiwara. Y Su/uki, Y Ouchi. H Take/.oc and A Fukuda 7/;/i J Appl Ph\s 27 L729 M9HH)[3] Yu P Panann, 0  Kalinovaskaya and J K Vi) Appt Phw. Lens 11 1667 (1998)[4] K Hiiaoka, T Tsunnla. Y Sugiyama, K Mon/cn, Y Dematau and Y Su/aiki Jpn J Appl Phys 36 (>847 (1997)15] Y Lee, A D L Chandam, K Itoh. Y Ouchi, H Takczoc, A Fukuda Jpn J Appl Phv\ 29 1122 (1990)[6] H Oiihara, T Fujikawa, Y Ishibashi, Y Yamada, N Yainamolo, K N|on, K Nakamura. Y Su/iiki, '1 Nagiwaia, 1 Kawanuira Jpn J Appl Phys 29 L^^ (1990)[7] J W O’Sullivan. Yu P Panann, J K Vi|, A J Seed. M Hird and .1 W C^ Oi\hy Mol Cr\M I iq Ciys! 301 189(1997)[8] AJ‘M Biradcr, S Wr6bd and W Haase Pins Re\ A39 2693 (1989) [91 Haase. 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Observation of Successive Phase Transitions in Ferroelectric Liquid Crystal (Cs-1013) from Dielectric Measurements and a Pseudospin Type Model for Studying Ferro and Antiferroelectric Behaviour

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Observation of Successive Phase Transitions in Ferroelectric Liquid Crystal (Cs-1013) from Dielectric Measurements and a Pseudospin Type Model for Studying Ferro and Antiferroelectric Behaviour

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