Darwish, A M

Eli-Mousely, M M

Nassar, A M

IACS Institutional Repository

Indian J, Phye. 50 , 0 0 9 -9 7 1  (1976)Effect of vanadium ions on the conduction mechanism of cabal glassesA. M. Nassak*, M. JVI. El -Mousely and A. M. Dahwish Faculty of Science, Ain~8hams TJuivenniy^  Cairo, Eyypt {Received January 197(i)TJd* cflact o f  small amount o f V.2O5 111 tho D.C. eloctric conduction o f cabal glasses AA'^ as studied, in order to itlontify, tlie nature o f conduc­tion mechanism, as well as the current cairiors in such glasses The results obtained giv<; a strong evidence that the divalent Ca‘‘  ^cations arc the main current carriers in glasses wiUi low vanadium concentration. With high concentration more than 2 % tho supci- position o f the electronic conduction on the larger activation energy of ionic conduction may show slight increase in the (lonductivitj^1. IntroductionTho commonly obscu’ved high resistivity ((hven 1961, Hiiayama 1962) of tho glasses in the system RO, B^Og, Al^Og have boon explained by Hirayama (1962) by consider ing the motion o f tho divalent cat,10ns iindci tlu‘ act,ion ol the applied electric field. Tho ease o f motion ot such cat ions is limited by the bond strengthS. Tho possibility o f the migration of the doubly charged ions, through the glass matrix has been inv'estigated by diffusion experiments using radio-active isotopes. Tho results o f JVlyuller it Pronkin (lOOti) give a pi.vTufid basis lor the j>robability o f migration- Also the more recent, studios on diffusion made by Frischat (1966, 1969) are jn consistenc*e wit h sneli point o f vioiv On the other hand the excep­tionally high values o f resistivity and activation eiieigj^ of these glasses have boon explained by Owen (1961) by considering that tho charge earriers to be the iion-bridging oxygen ions On the other hand the eloctiical conductivity of high vanadate glasses (JVIackenzio 1965, Dale it Stanworth 1954, Denton ct al 1954, jyiyuller 1968) 1ms been explained on the basis that the electrons arc the current earners in these glasses.In oj’dcu' to identify the nature of the current can iers in the present studied irlasses, it has lx*eu decided t(, apply the theoretical concepts ot JMyuller (1968) about tho electrical conduction in oxide glasses On basis ot these concepts, the authors have calculated the experimental value o f tno modulus of conduc­tivity for Ca'^ A; cations in these glasses. Tho calculation was canied outby using the relationm(T^' =  v4—log [JfJwhere A is the value o f the intercept (d the log rr vs 1/T plot at 1/2’ =- 0 ; and [M\ is tho ooucentratioii o f ions in mole/cc.* Ghrla College, Al-Azhar LTniversity, Cairo, Egypt.9692. Experim ental Procedure  (tt) Haw material and glas,s mdls :Tho glRMR .‘samples haie been prepared in balclies of 50 g Analar grade eliomioalH have lx‘-en used was introduced as bone acid, AhOs andwor(i mtrodiiced as such, wliilo CaO Avas used in the fciJin of (sarbonato.The melting Avas c;arried out jji J*t 2% Kh cnicibles m automatically eontj olled oloctric fui'Jiacc at tompeiature of 1400'’C il0 '*C  for four hours. After melting tho molten glass was castod in iron moulds and transferred immediately to the annoaling furnace ai- the appropi iatc temperaf.uie lor (piajltT of an hour aftei' Aidiich the furnace begins cooling AAith the jiroptu- rale of cooling in order to get stress and strain free samples. The base ('ompositioii of the glassc^ s prejiarcd is CaO 38; B.Og 41; AI2O3 2 1 .(b) The D.O. r/ynductiriti/ weamre.'we'Ht,^  .Sam])Ics of mie square cm aica and of 0  .3 f.o 0  1 cm thickness with pai’allel sides of tolerance 15/i ares used. Ihe samples faces ar(‘ coati'd A>iith aqua-dage and before being dried the electrodes AA^eie applied.The D.O. conductivil'Y was measured using a vibrating read electrometer type VAJ 51, measuring crirrents up to 10'^  ^ Amp Surface conductivity has been tested by using the guard ring method. Jt Avas found that the surface conductivity represents a fraction AAhich does not exceed 1%; thus it is negligible3. R esults and DiscussionThe results obtained .shoA^ 'n in figun* 1, from Avhicli it. is noticed tliat the relation botAA^ oon log <7 and 1 jd' is a linear relation in the measuring temperature970 A, M. NaBsar, M. M. El-Mousely and A. M. DarwishFjg. 1 Log tSpeiiific conductivity versus i“eciproca] of absolute temperature fer 7 glasses in the systom (ca0 ;B20a;Ala03) oeutaining different concentrations of V2O5 The numbers correspond to tho numbers of glasses in table.range (530 to 610“K), This iiidicat-es tlia-1. ihe iiatui’O of the principle conduc­tion mechanism in such glasst^ s does not changes with the used VgOg concentra­tions Table 1 shows the average ealuos of the cliaracteristic electric (piantilies by log (Tjo,,. acl ivation energy E, and the value of A sith their deviation.Table 1Effect of vanadium ions on the condMction mechanism 971GrlassNo.log O-jft,, JU(K oal /molt)) A [ O | ' '1 0 ' » v,ogm1 - ] 3 . 9 2 - t 0  0 6 8 2  8 6 2  : L 0  3 2 3 3  6 9 6 1 .8 G 2 : L 0 .1 0 G 3 7 1  - 0  G 8 2 .1 2 -2 1 3  H 5 i , 0 8 1 , 8 1 1 4 : 0 3  5 4 0 1 7 6 4  1- 0 3 . ( 1 0 8 - 0 . 7 8 2  11 0  211 - 1 3  H c y o . i 8 2 . 3 5 1 4 : 0 . 4 1 5 3 .5 6 0 1 8 9 1  J O .O S 3 . 6 4 2 - 0 . 7 8 2 . 0 .5 8 64 - 1 3 . 8 5 ± 0 . ( ) 5 8 1 . 8 7 4 - h O 3 .6 4 6 1 7 8 8 4  0 .0 4 8 3 . 6 3 2 - 0  7 8 2  9 6 1 .05 - 1 . 3  8 0 ± 0  0 1 6  8 1 . 6 0 0 J - 1 . I S 3 .6 3 6 J . 7 6 8 4 _ 0 .2 2 G 3 . 6 1 6 - 0 . 7 8 2 . 6 3 1 60 - 1 3 . 7 a i 0 . 0 2 8 2 . 0 0 0 4 - 0 . 0 5 3 .6 4 8 1 G l l - J i O . l 3 4 6 0 -  0 .8 8 2  4 5 2 .07 - 1 3 . G 2  J 0 .1 G 2 7 9 . 4 9 6 4  1 .3 0 3 4 4 4 J 6 3 8 4 _ 0 .4 2 9 3 . 4 0 6 - 0 . 9 8 2 .3 8 4 .0I’ho bii.so p la sB  iiflfid  having the e o m p o i i i l .K m  ;i8UaO/4] BaO^ ; 21 AljOj it) m o l e .I^ 'rom ligiircs 2 and 3 it is clear that the addition of \^ O^r, in the given 1‘egion of concentration, results in a very small (negligible) decrease in the value of tlie activation energy K for the base glass (having Vi- 'S2-85 K.cal/molei: and a corresponding slight incji'ase in its log <t {crt — 13-92).Fig 2. Relation between log. ajisoifie oondiiotivity (at .S00°C) and YaOj ponoentration m cabal glass.The values of the intercepts {A) given in table (1) are used to calculate the experimental modulus of conductivity for Ca2+ cations. The calculatedvalues together Avith its deviation A/atr from the theoretical A"alue 4.3d-1 ar® given in table 1. It is clear that the deviation A?ko- <  1 for all the studiedsampleH, mdioate tlie agi eomont of the experimental with the theoretical moduli of conductivity for Oa^  t cationK This may be taken as an evidence for eonsidei'- ing Ca® '' as the mam current carrierB in all the studied tramples.972 A. M. NaBsar. M. M. El-Mousely and A. M. Darwiflh(3) Rolalion botwoon tlio activation onorgy E(ni koal/molo) and the ooncontratioii of VgOs in c-ahal glassThe observed decrease of the activation energy and the increase of the (‘on- dnetivity ot sample lio. 7; may be attributed to either of the ; for (a) The el^nge of the conditions of binding of the cat ions t o the oxygens of the network dn<^  to the introduction ol V2O5, 01 (b) The increase of the electronie ]iart of ciondne- tion mechanism with the* pvc'seuec* of vanadium 10nsThe change of the condition ot binding ot the Ca^ + cations affects the valuer of the dissociation energy of these ions fi'om their polar sites (Myuller 19fi8), and cjonsequenily the activation energy 7? and the specjific conductivity cr. This effect can bo tested by the strength of oxygen backing (Schwart z ei al 1966, Rao 1963) |0), and which cjan be cjalculatcd using the relationCao+ 3  ( H-3' ALO + 5 \M)Jwhere is the c'xperimental determined glass (icnsit,y; a and M  are the weight tractions and the molecular Aveiglit of the corresponding oxides m the glass, respectively.The calculated valui^ s are given in table 1, from the inspection of this table wo note that {0 1 does not change and has an average value of 82-4 x lO-^ * niole/cc Therefore, it seems that the piogiessive addition of within the given region, does not change the condition of lu their polar sites in the glass structure (Rao 1963). Accordingly it may bo concluded that the observed small cliangesm both E and log traoQ for Htimple No 7 (jaiinoi. bo attribiiiod to tho dccTease of the disBooiation onergy (if Ca-' rations.The iiicr<ia8e of the electronic pai-t of condnotion due to the inirodiiclion of vanadium ions; which acts as sources loi the electrons livailable for the cimduc- tion procosaes (Mackenzie 1965) acH’ording to a mechanism denot'd as tln‘ mixed valence mechamsm. In this niochaiiism the electron motion is a sc^ rjes ol hopping between the two valencies and , as represcntc'd byV41 —0 — 1- -> ' —0 —v^+It is known that the electronic conduct ion is largely affected (Owen 1970) by the separation a^  between tin’s vanadium ions. Tliis separation was calculated using the relationEffect of vanadium ions on the conduction mechanism 973r MFor the glass No. 7 we gi'i a value for the V—V separation Uq =  11 A This value of separation may be too largo to be jumped by electrons, liopping from one V ion to anothci during the process of conduction. But on the other hand, it has hecn stated by Mackenzie (1905) tbat the large separation between the. transition inoial ions in glass, in the fiiestMU’c of oxygen ions bciw'ccn two sidtes of hopjiing dex^ s not prevent, th(‘ hopping nxiclia-nisiu Accordingly; one may suggest that,, in spite of tlic relalividy large .separation between t,hc two V ions ill our glass No 7, there’, may be a (letiuite pT’obability for an electron to hop this distance and to afhjct, th(* conduelhjii, this w^ as shown by Myulk'r (1905, I960) to bo pnjbable in oxygen glasses,Chueral co7ivlusion :The D.C. conductivity of ,sueh glass is not affected appieeiably by the exist­ence of low'^  concontration of vanadium The conduction is mainly due to ionic tran.sport of Ca2+, and at Jiigh eoiieentration of vanadium superposirien of the electronic contdibutioii is slightly observed Lastly no ovidonco for condutlioii by non-bridging oxygen ions as previously suggested by Owtii (1961) This last suggestion had been reached from another w^ ork in the same laboratory, which will bo published elsewhereR eferencesDttlo A. E. &. 8taiiwoith J. E. 1054 Research, homlon 7, 3S.Benton E P , Rawson H &. Stanwoith J. E. 1054 Nature, London 173, 1030.FriHchat ('. H. &, Hoirboit J. 1900 OeL (Uaeteeh Bar , 39, 524.Fi'isehai C. H. 1960 J. Amer. Ceram Roc., 52. 025.Mackenzie J. D. 1965 Modern aspects of the vitreous state vol. 3. pp 126, London Butterwortha.974 A. M. Nassar, M. M. El-Mousely and A. M. DarwishMyiiller R. L. 1965 Structure of QlasB . Electrical properties of Glass Vol. 4, pp. 64, Ertileri by Mazunn, Consultant Biuoau, New York.Miiyllor K. L. 1960 Solid state chemistry, pp (1), Consultani Bureau, New York.Muyller R & Pronkin A. A 1966 Solid state chemistry, pp 121, Consultant Bureau NowYorlt.Muyller R, L 196K Glassy state (collection), Jzd Aknd. Nauk SSSS, Moscow-Lmongrad, pip. 67. Owen A, E 1961 Jfhys. Chem of Glasses 2, 87 Owen A, E 1970 Contemp. Phys 11, 227•lanakirama Rao 19611 Phys Chem of Glasses 4, 1, 22.Schwartz M. & Mackonzio ,1 D 1966 J. Amer Ceram. Soc. 49, 583.Wasfy N- 19,65 Some propeitics of silicate and horaic glasses contaimmj Ti in relation to structure,M.Sc. Thesis UA.C.

Effect of Vanadium Ions on the Conduction Mechanism of Cabal Glasses

http://arxiv.iacs.res.in:8080/jspui/bitstream/10821/4630/1/Effect%20of%20Vanadium%20Ions%20on%20the%20Conduction%20Mechanism_A%20M%20Nassar.pdf

Effect of Vanadium Ions on the Conduction Mechanism of Cabal Glasses

Abstract

Similar works

Full text

Available Versions

IACS Institutional Repository