Frreda, T H

Sancta, Albin J

Sutha, Gnana A

IACS Institutional Repository

7 , phys. 75A (3). 245-247 (2001)U P  Ann tmcrnaiional journalElectrical conductivity measurements on gel grown KDP crystals addedwith KCl and KNO,J A lb in  S an cta , A  G n an a Sutha, T  H F recd a* , C  l^ a h a d cv a n *  and C  B a la sin g hOepaitment of Physics, Scotl Chn^tian College,Nagcrcoil 629 003, Tamiinacii, India T Hindu College, NagercoiI-629 (K)^ , Tumilnadu, IndiaE-inatl mahadCs>sancharAel in R a e i v e d  R S e p te m h e t  2 0 0 0 , a v ( e p le d  S e p te m b e r  2 0 0 0\bsiract Pure and iinpuniy added (with KCl and KNOJ KDP single crystilis were grown by the gel method using silica gels ElectricaloM(iiiciivity measurements were earned out along both the unique axis and perpcndiculai directions at various iciiipcratuies ranging Irom 40 to 130‘Ct \ ihc conventional two-probe method The present study shows that the conductivity in KDP crystals incieases with the increase in impurity,.ntcontiation and temperature Activation energies were also determined and reportedKeywords Electrical conductivity and impurity added KDP crystalsPACS' Nos. 72 15 Kl, 61 72 ,Ss,1. IntroductionI'niassiiim d ihycirogen  tirth op h osp h atc , KH^PO^ (abbreviated  as KDP), c ry sta ls  h a v e  crea ted  co n s id e r a b le  in terest a m o n g  seveial research  w ork ers [ l-b ] . A  research  program m e on  the  giovvih and p h y sica l prop erties o f  pure and im purity added K D P  ciNstals is on  hand in th is laboratory. A s a part o f  the program m e, Nve have stu d ied  th e e ffe c t  o f  io n ic  im p u rities  (K C l, the very  mieresting a lkali h a lid e , and K N O ^, an in o rg a n ic  ferroelectric  material, added h e a v ily  (im p u rity  added  in the K D P  so lu tio n  Used for the g ro w th  o f  c ry sta ls  w ith  im purity  co n cen tra tio n  ranging (rom  2()()0 to  l( )0 0 0  p p m . i . e ,  0 .2  to  1.0  m o le  %)] on  the electrical c o n d u c tiv ity  at va r io u s tem p eratu res ran g in g  from  4 0  lu 13trc o f  K D P  c ry sta ls  grow n  by the g e l m eth od . A lread y  w e  Iravc reported the resu lts o f  our earlier study at room  tem perature (32"C) [7]. W c report here the resu lts ob ta in ed  in our pre.sent t^udy.ExperimentalSingle crysta ls w ere  g ro w n  by u sin g  the p ro ced u res reported  curlier (6 , 7 ]. S o d iu m  m e la s il ic a te  so lu tio n  o f  d en sity  1 .0 8 g /cc  'vus used. A n a ly tica l reagent ( A R ) grade sa m p les o f  the required  clicmicaJs (KDP» K C l and K N O ^) a lo n g  w ith  d o u b le  d is tilledf f’rresponding Authorw ater and eth y l a lco h o l w ere u sed . K D P  w a s added  w ith  KCl and KNO^ sep a ra te ly  e a c h  in s ix  d ifferen t K D P  : im purity  m olecu larratios,vc . l:0.(X X )(purcK D P), 1:0.(X)2, l:0.(X)4,1:().(KX>, 1:0.CX)8 and 1:0.010.S ca icn o h cd ra l m o rp h o lo g y  ( tw e lv e  s id ed  p o ly h ed ro n ) w as  ex h ib ited  by all the cry sta ls  gro w n . A ll the grow n  crysta ls w ere  found to be very sta b le , c o lo u r le ss  and transparcnl. C rysta ls  w ith  h igh  transparency and large d e fc c l-fr c e  s i / c  (>  3 m m ) w ere  se lec ted  and u.sed for the e lec tr ica l co n d u ctiv ity  m ca.surem cnts. T he ex ten d ed  p ortions o f  the crysta ls w ere rem oved  co m p le te ly  and the o p p o site  fa ces  w ere  p o lish ed  and c o a led  w ith  g o o d  quality  graphite lo  obta in  a g o o d  o h m ic  co n ia c i.T he co n d u ctiv ity  m ea su rem en ts w ere carried out a lo n g  both  the un ique a x is  (c>) and p erp en d icu la r  (a - and h-) d irec tio n s for all the e le v e n  cry sta ls  grow n  u sin g  ihc co n v en tio n a l tw o-p rob e  tech n iq u e at various tem peratures ran gin g  from  4 0  lo  I3 0 % \  T he resista n ce  o f  the cry sta ls  w ere  m easured  u sin g  a M eco  m ultim eter. T h e o b se r v a t io n s  w ere  m ad e w h ile  c o o lin g  the sa m p le . T h e d im e n sio n s  o f  the cry sta ls  w ere m easured  u sing  a travellin g  m icro sco p e  (1.. C . ~  ().(K) 1 cm ). T h e co n d u ctiv ity  ( o ) o f  the crystal w a s ca lcu la ted  u sin g  the relation(J =RA©2001 lACS246 J  A lbin Sancta, A Guana Sutha, T  H  Freeda, C  M ahadevan a n d  C  B alasinghwhere R is the measured resistance, d ihc thickness of the sample and A the area of the face in contact with the electrode.Plots between ln(cT7’) and 10(X)/T were found to be very nearly linear. So, the conductivity values can be fitted to the relationa 7 ’ = <T oC xp(-£/^r),where E is the activation energy, k the Bolt/jnann constant, T the absolute temperature and the parameter depending on the material. Activation energies were estimated using the slopes of the above line plots |£ =  -  (slope) k x IfXK) ].When the cry.stals arc grown in gel media, there is a possibility that the conductivity and related properties arc different for different crystals even though they are grown in the same container. It would be better if there is a possibility to estimate quantitatively the concentration level of the impurity that is present in each crystal. But, it is very difficult to do so since the impurity concentration is < 1%. Hence, in order to understand qualitatively (atleast) whether the added impurity has entered into the KDP lattice or not, wc carried out the density measurement by using the floatation technique.3. Results and discussionIt was observed that the difference in densities of crystals grown in the .same container was very small and negligible. Average densities are given in Tabic 1. The value observed for pure KDP (2.344 g/cc) compares well with that reported in the literature (2.338 g/cc) [8|. The observed decrease of density of KDP crystal caused by the impurities indicates that the impurities have entered into the lattice of KDP crystals. Moreover, it can be seen that the density decreases further with the increase in impurity concentration of the aqueous solution of KDP used for the growth of crystals.The a  values obtained along the two directions (a-<iiuiTable 1, IDen.stties and activation energiesSystem Density(impurity in inolc%) (g/cc)( a )  P u re  K D P  2 3 4 4(b )  K C l added  K D P0 .2  2 .2 3 30 .4  2 .2 2 30.6 2.2200 .8  2 .1 9 31 .0  2 .1 9 2( c )  K N O , added  K D P0 .2  2 .2 9 70 .4  2 .2 8 80 .6  2 .2 7 80 .8  2 .2 5 91 .0  2 .2 4 2Activation energy, E(eV) along ^/'direction -direction0.2200  4 2 7  0 .4 3 8  0 .4 3 0  0 .4 1 5  0 .3 8 10..3910 .3 8 40 .3 8 90 .3 9 90 .4 0 50 .2 1 60  3 8 9  0  3 9 3  0 413 0  4 0 6  0 .3 7 00 .3 9 0  0 .3 4 4  0  3 4 7  0 .3 3 6  0 .3 3 8b-) perpendicular to the unique axis (c-direction) are. wiih„i | experimental error, the .same. Figures 1-4 show the plots,,' In(aT) against 10(X)/T for the pure and impurity added Kl)[> crystals. The values of the activation energy E for puie impurity added KDP crystals arc given in Table I .Figure 1. Variation ot !n(<j7’) with lOOO/T along a-clirccimn Kt; added KDP1000/TFigure 2. Variation of Inter/’) with lOOO/T along c-dircction foi K( I added KDP.100CVTFigure 3. Variation of ln((T /') with lOOO/T along a-diiection for KNO added KDP.Conductivities obtained in the present study, are of the same order with those obtained by previous authors for the KDI’ crystals (x 10^  mho/melre) [2,5-7,9,10J.It can be seen that for both the impurities considered in the present study, the electrical conductivity increases with the increase in impurity concentration and temperature. ThisE lectrica l conductivity' m easurem ents on ^ e l ^row n K D P crystals etc 2 4 7iiiiilar 1 0  that observed for oxalate [2J and ammonium compound |f,| added KDP crystals. The defect concentration will increase (Exponentially with temperature and consequently the electrical (,nducuon also increases. The addition of impurity further f^iifeases the electrical conduction in the temperature region ^insidercd. This can be explained by considering the ^placcineni of (H^PO^r* ions by Cl * and (N O ^r‘ ions.Pure KDP1 0 002 1 0 004 1 0 006 1 0 008 ♦- -1 0 012 4 2.5 2.6 2.7 2.8 2.9 3 0 3 1 3 2 3 3 3 4100CVTimirc 4. Variation on ln(<r7') with lOOO/T along C'dircction for KNO,Adi.'A KDPrhe electrical conduction in KDP crystals has been sLiblishcd 111-12] to be protonic. In KDP type of crystals, the iM.sihle type of point defects which help the electrical nruluction process are the ionization defects, viz (HPO^)^ and H PO^), produced as a result of proton jum p from one Miosphatc group to another along the same bond |13| and L ind 1) defects.Jaccard and his coworkers 114, 151 have shown that proton onduclion may be accounted for by motion of protons iLCoinpanied by a D defect (excess of positive charge), digralion of these defects may only modify electric polarization ind may not change the charge at an electrode [14]. The motion 'I d e l e c ts  occurs by some kind of rotation in the bond with ktecis. The speed of displacement v = D r/, where a and D arc lie distance and frequency respectively of the jump from one )ond to the other.H the sample crystal is placed in a stationary electric field (as M the present study), the carriers may be considered to be *mtaincd in an enclosure bounded by the capacitor plates. As he carriers may not leave the enclosure, they accumulate in the egions close to the plates which causes a concentration radient lo be formed and this gradient feeds a diffusion current. 1^ equilibrium, the diffusion current density equals that of the Init current. Charge accumulation is related to inhornogencities ‘1 the material, the agglomeration of impurity ions by diffusion n the vicinity of electrodes or chemical changes in layers close ‘^ electrodes [16].The conductivities arc more along the a-direction than those ‘h>ng ihc r-direction for both the impurities considered in the t^cscnl study for all the impurity concentrations and all temperatures considered. This is in correspondence with the t^ sults obtained by the previous authors for their systems 2e6,9).The E values arc more along f/-direction than those along c- d irection for both the im purities for all the im purity concentrations. However, there is no systematic variation observed with the impurity concentration.The conduction region considered in the present study, seems to be connected to mobility of vacancies. The low activation energies observed suggests that oxygen vacancies may be responsible for conduclnm in this region. The present study gives further evidence to the statements : i) the electrical conduction in KDP crystals is protonic ; and ii) the electrical conduction in KDP crystals is mainly due to the anions vi: (H^PO^]^* ions and not the cations viz. K^ ions.4. Coi|clusionsPure an j impurity (KCI and KNO,) added KDP single crystals were grown and electrical conductivities were measured along both the a- and c- directions at various temperatures ranging from 40 to 130‘'C. Density measurement indicates that the impurity molecules have entered into the lattice of KDP crystals. The present study gives further evidence to prove that the conduction in KDP is protonic and mainly due lo the anions and not the cations. The present study indicates that the conductiv ity  increases with the increase in im purity concentration and temperature. At low temperatures, the conductivities are more along the ^/-direction than those along the r-direction.R e f e r e n c e s19110IN[12(13[14(15[16K n R Varma, K V Rainanajah and K V Rao H ull M a tc i S i i 5  (198. )^M Shanmuphani, F D Cjiianam and P Rainasamy tm i ia u  J  P u ie  A p p I  r i m  23 82 (1985)H K Hcnisch t f i  Gels ami Ijese^anj  ^ R m f^K  (CambridgeCambridge University Press) (1988)L N Rashkovicb K D P -F a n ii ly  Suijifle  C 'rystal.s (New Yoik Adam Hilgcr) (1991)K vSomasekhara Udupa, P Mohan Rao, .Sriramuna Aithal. A P Bhat and I) K Ava.sthi H u ll M a te r  S t i 20 1069 (1997)T H Freeda and C Mahadevan H u ll M a te r  S e t 23 135 (2(K)0) Bcuuluh Shanthini, C Anitha, C Mahudevan and C Balusingh In d ia n  J  P h y s  73A 805 (1999)John A Dean (Edn) L a i i f i e 's  H a n d b o o k  o f  (Z h e n u U iy  XII edn (New York ■ McGraw-Hill) p4 (1979)L B Harris and G J Vella ./ A p p !  C h e  n r  17 151 (1966)P .Sekar Rama.subramaman and C Mahadevan In d ia n  ./. P u re  A p p I  P h y s  29 285 (1991)M O' Kcdfc and C T Perrmo J  P h y s , C h em . S o l id  2H 211 (1967)M Shuninugham, F D Gnanam and P Ramasainy I n d ia n  J P u r e  A p p I  P h y s . 20 579 (1982)A W George N u r l  In s tr u n i .  M e tf i  P h y s  R e s  B29 708 (1989)H Granicher, C Jaccaid, P Scherrer and A Steinemann D is c u s s  F a r a d .  S o e  23 50 (1957)C Jaccard H e  tv. P h y s . A c ta  32 89 (1959)I Bunget and M Popcscu P h y s ic s  o f  S o l id  D ie le c tr ic s  (New York . Elsevier) (1984)

Electrical Conductivity Measurements on Gel Grown KDP Crystals Added with KCL and KNO3

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Electrical Conductivity Measurements on Gel Grown KDP Crystals Added with KCL and KNO3

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