Kumari, Kiran

Sharma, H

Singh, H S

IACS Institutional Repository

Indian  J .  P hys. 73A (6), 801-804 (1999)WOTE U P  A- an in ternational jou rna lStructural and dielectric properties of KBasTiNb9O30 ferroelectricsH Sharma, Kiran Kumari^ and H S SinghU n iv e rs ity  D e p a r tm e n t o f  P h y sics, V eer K u n w ar S in g h  U n iv e rs ity .A rra h -8 0 2  301 . In d iaReceived 28 May /999, accepted 25 June 1999A b s t r a c t  : P o ta s s iu m  b a riu m  tita n iu m  n io b a te  (h e re a fte r  P B T N ) h av in g  co m p o sn io n  K B a 5 T iN b 9 O 30  has b een  sy n th es ized  by  h ig h  te m p e ra tu re  so lid -s ta te  reaction  techn ique. Room  te m p e ra tu re  X -ray  d iff ra c tio n  (X R D ) studie.s o f  th e  co m p o u n d  show  that it has a te tragona l s tru c tu re  w ith  la ttic e  p a ra m e te rs  a  =  /? = 1 2  43  A and  c =  4  1 0  A M easu rem en t o f  d ie lec tric  c o n s ta n t fro m  liq u id  n itro g en  tem p e ra tu re  to  4(X)°C su g g ests  th a t the  m ateria l is fe rroelec tric  at ro o m  te m p e ra tu re  and  tran sfo rm s  in to  a  p a rae lcc tric  ph ase  at a round  290^^0K e 3^ o r d s  ; T e trag o n a l s truc tu re , d ie lectric  constan t, fe rro e lec in c  m a icnalP A C S  N o s. : 61 .7 2  D d, 77 84 D yPotassium barium  titanium  niobate (KBa5TiNb903o) belongs to a ferroelectric oxide family of tungsten-bronze (TB) structure [1] of general formula AB5TiNb903o {A = Na, K and B = Sr, Ba). The tungsten-bronze (TB) structure consists of a complex array of distorted B06 octahedra sharing com ers in such a way that the different types of interstices (y4|, A2 . B\y B 2 and C) are available for cation substitution [2]. The polar axis of most of the m em bers o f  TB fam ily is norm ally c-axis. A wide variety and range of compounds ol tungsten-bronze (TB) type has been studied. Some niobates with TB structure such as barium  sodium  niobate and potassium  lanthanum niobates [3] are quite attractive and interesting ow ing to their wide industrial applications. Studies of structural and dielectric properties o f  som e ferroelectric oxides o f TB structure 14,5] have been reported. The electrical conductivity m easurem ents of a few compounds [6] also confirm the occurrence of offset near the transition temperature.P rese n t A d d re ss  : D e p a r tm e n t o f  P h y sics. D r S K S M  C ollege. M olihari-845  401 © 1999 I ACS802 / /  Sharm a, K iran  K um ari a n d  H  S  S in ghA literature survey reveals that even though the compound has been suggested to be ferroelectric, no systematic X-ray and detailed dielectric studies have yet been reported. We, therefore, present in this paper preliminaiy structural and detailed electrical (dielectric constant (e)  and loss (tan 5)) properties of the PBTN compound.The polycrystalline samples o f PBTN were prepared by a standard high-temperature solid-state reaction technique from the raw materials : Ti02 (99 % s.d. fine chem Pvt. Ltd.), Nb^O^ (99.9 % SMP), K2CO3 (99.9 % SM Chemicals) and BaC03 (M/s Ultra Pure LOBA CHEM IE) in a suitable proportion. These oxides and corbonates were thoroughly mixed in an agate-m ortar in alcohol for 10 h and dried. The dried powders were calcined in a crucible at 1050‘^ C for 25 h. The process of calcination and m ixing was repeated till the final hom ogeneous pow der o f PBTN was obtained. The form ation and quality of the com pound were checked with X-ray diffraction technique. Some of cylindrical pellets (of diam eter 10.3 mm and thickness 2.3 mm) were made under the isostatic pressure (6 x  10  ^ K g /cm ^) using a hydraulic press. The pellets were then sintered in air atm osphere at llO O X  for 10 h. A fter polishing and grinding, both the flat surfaces o f som e pellets .were electroded with air drying silver paints for electrical measurements.The X-ray diffractogram s o f the PBTN pellet sam ples were taken with CuK^ radiation (A = 1.5418 A) in a wide 26 range (20° < 26 < 70°) with Philips pow der diffractom eter (PW 1710 Holland).Figure 1. X-ray diffractograro of PBTN pellet sample.The dielectric perm ittivity (£ ')  and loss (tan S) were obtained on the sintered and electroded pellet sam ples as functions o f frequencies (500 Hz to 10 KHz) and tem perature (liquid nitrogen to 400^C) using G R  1620 capacitance m easuring assembly. T he re lia b ility  o f  the  da ta  w as checked  by repeating  the  ex p erim en ts  w ith d iffe ren t instrum ents (LC R -H igh tester, H ioki 5530, Japan) in the sam e physical conditions.S tru c tu ra l a m i  d ie le c tr ic  p ro p e r tie s  o f  K B a J iN h .O ,, ,  fe t to c ic c tn c s  8 ( ) 3F o l lo w in g  the  da ta  g iv e n  in  K a n d o lt-B o rn s le m  lab los |7 ],  a ll ihe p io m m c n i peaks  in  F ig u re  I w e re  in d e xe d  u s ing  te tra g o n a l u n it ce lls  A good ag ieem en t b e tw e e n  the  o b se rv e d  and c a lc u la te d  d -v a lu c s  suggests that the cho ice  o f  un it c e lls  IS c o rre c t and the c o rre s p o n d in g  la ttic e  param eters are a  ^  h =  12.43 A  and ( = 4 ,1 0  AF ig u r e  2. V a ria tio n  o( tJicIct-liiL pc im i(iivn>  and d u 'lc t l iK  loss Man w ith  te m p e ra tu re  at i\vo ttccjiiciK ics I kH z am! 10 KHzFigure 2 shows tluit the varialm n ol dicloclnc pcim iuivii) i r ' )  .iiul thdeelru* loss (tan S) with temperature at two licquciikics 1 kHz and 10 kH/ Ii is evident (nnii this figure that thd dielectric pcrnnUivit> inuea^es oiadu<ill> abo\e nunn lemperalure and becomes maximum around 290^'C\ The dieleetiit h's^ on the other li*ind incieases up to about 29()®C and then levels off. The leason lor levelling oil may he due to meieascd ac conductivity of the sample, Tdie peak in the tiieleuriL pennim \itv  t r ')  aiound 290”C is indicative of ferroelectric phase iransiuonIt is thus concluded that PB'FN is tetragonal at mom lempeiaiiire ami it may possess ferroelectric property with a lenoeleetiik (ihase iiaiiMtion lempeiature of 290'C which is quite high as compared to other membeis ol the fam ilyAcknowledgmentWe thank Prof. R N P Choudhary I I T Kharagpur lor st.nic cxperimcnlal help and kind encouragement.References[1] M E Lines and A M Glass Pnnuples and Applu atams ,•! FeiK-rlt; m ,  ^ ,/»./ /M a u  d U a irn a h  (Oxford University Press, Oxford) (1977)[2] P B Jamieeson. S C Abraham and J L Bernstein./ r/ii-ni Pin  ^ 48 *>04811 ‘)(A i804 H Shdrm, Kiran Kumari and HS Singh[3] L G Van Uiteit, S Singh, H J Levinstein, J B Gensic and W A Bonner Appl. Phys. Lett. 11 161 (1967)[4] R N P Choudhary and B K Choudhary J. Mater Set. Lett. 9 391 (1990)[5] R N P Choudhary, S Bera, K S Singh and R Sati Indian J. Pure Appl. Phys. 31 738 (1993)[6] N K Mishra, R Sati and R N P Choudhary Indian J. Pure Appl. Phys. 34 96 (1996)[7] Landolt-BOmsicin Tables Vol. 16 (Springer-Verlag Berlin, Heidelberg. New York) (1981)

Structural and Dielectric Properties of KBa5TiNb9O30 Ferroelectrics

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Structural and Dielectric Properties of KBa5TiNb9O30 Ferroelectrics

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