The project 'Synthesis of Ultrafine Ba0.7 Sr0.3 TiO3 by Mechanically Activating Process' was successfully completed early 2008. As reported in the technical report attached, the single phase BST was produced successfully at a relatively low temperature of 500oC, albeit the challenges encountered during the synthesis, one of which is the caking problem as well as melting of phase formed. The caking effect was due to the mechanical activation process, while the melting phase was a result of the low meting chemicals used

Mohd Noor, Ahmad Fauzi

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.End Of Project Report(NIPPON SHEET GLASS)Period : 2005-2007Project Title:Synthesis of [Iltrafine Bas.TSrs3TiOr byMechanically Activating ProcessProject Leader:e"6Professor Dr. Ahmad Fauzi Mohd NoorTel:05-5946174Fax: 05-599101 IProbsor Dr. Ahmad Fauzi Mohd NoorPusat Pengajian Keiuniteriaan Bahan & Sumber Minerallcrnpus KejuruteraanUnivenitl Sains Malaysia,14300 Nibong Tebal, Pulau Pinang.Tef:604-599 6174 Fu:604-594 1011Synthesis of Ultrafine Bas.7Sre3TiO3 by Mechanically Activating Process1. SummaryThe project 'Synthesis of Ultrafine Ba6.7Srp.3TiO3 by Mechanically Activating Process'was successfully completed early 2008. As reported in the technical report attached, the singlephase BST was produced successfully at a relatively low temperature of 500oC, albeit thechallenges encountered during the synthesis, one of which is the caking problem as well asmelting of phase formed. The caking effect was due to the mechanical activation process, whilethe melting phase was a result of the low meting chemicals used.Calcination at 500oC wasthe lowest that we can achieved in this study. It was found thatduring sintering, the next stage of product formation, the pellets prepared from 400oC calcinedmixturc crackcd ofter sintering. This is due to insufficient decomposition at 400oC. Furthersignificant decompotion took place during sintering which caused the pellet to crack.The dielectric properties obtained in this studies were relatively low as compared to thosederived from conventional solid state reaction route. The dielectric properties are most optimumin the grain size range of 2-5 pm, and subsequent declined if the grain size is smaller or bigger.Therefore ultrafine powder is expected to yield lower dielectric value, however it makesminiaturization possible which is crucial in electronic field. Furthermore, the decomposition ofthe remnant phase of BaCO: and SrCO: in the calcined powder contributed to the porousmicrostructure; hence degraded the dielectric properties.2. Period of research conducted : 0112005 to April 2008The research was approved from Jan 2005 to Dec 2007. There was an extension of of afew months to the period of research. This was due to some complication in the beginning of thefunding of the project. Although there was indication of the approval of the project, but thefunding disbursed was only received middle of July 2005. Nevertheless, the project proceeded onafter the fund was received.3. Amount of fund :Received: RN137,643Spend: RM35,600Balance: RM2.0434. Staff involvementI Final Year Project student1RAI PostDoc (supporting project)5. Purchase of equipment: None6. Publication: ITeoh Wah Tzu, K.Sato, Ahmad X'auzi M.N.; Properties of Ba0.7Sr0.3TiO3 Synthesised FromMechanically Activated Ba(OH)2.8H2O-Sr(OH)2.8H2O-TiO2 Solid System by Mortar Griningand planetary Milling, ITE Letters on Batteries, New Techniologies and Medicine, Vol.8, No. 3,(2007)ConclusionThe project has been completed, with a successful outcome of synthesizing single phaseBaSrTitanate. Upon sintering, it was found that a low dielectric constant material was produced,as compared to BST produced by solid state reaction. Nevertheless, the values achievd are stillwithin the range ot'typical dielectric materials.Further work will be continued to produced BSTwith optimum dielectric properties.Report prepared byProfessor Dr Ahmad Fauzi Mohd Noor.**-Tt - ts*|c.t hr^r 9,.c,crelk-lQa t'c"atrLuh<-"t-+ l. u- . , U .-,^rr.Hnul- {t" Sthg*ta.l1,.^r, . h,r.t .vn4.i\+{fl h pi"{n* JG. r;Jar.}d }ytrrr* hr}' cl-.ol.-rt^9tr'h^^tb. A ftr * ?y,bhrhd rJ ^B^9tr'h^ t F f"y ar8 r,&^.^tt , lt^r fd-tf' t'q w\d tt'r 9<fA4N gtrfor*ce. t .r4t .PROF. iyn oB. AzlzAN Azlzllmbolo e!,:'[Pengcli't,'P.P.Ker';; ', tt.', eenygl*Onl., i,.r:r&SuttllMinerolKomp. ,, r. :i '.Univeri, tr st.trr'5 lvl"J'oYsloA) Project SummaryBa(OH)z.8HzO-Sr(OH)z.8HzO-TiOz solid system had been investigated toproduce Bao zSro rTiO3 (BST) via solid state reaction by mechanical activation technique.Mechanical activation was performed to these solid systems by high energy planetarymilling equipment.In the preparation of single phase BST from starting materials of Ba(OH)z.8HzO-Sr(OH)z.8HzO-TiOz, remnant of carbonates are found in the solid system aftercalcination process; this was due to the localized inhomogeneous (caking effect) of thesolid mixture by planetary milling. However, single phase BST was successfully derivedfrom the sintered pellet of BST. The mechanically activated particle also achievedultraf,rne size at the range of 200 nm. The powder is the undergone pelletization followby sintering. Single phase BST was achieved for all the pellets sintered at i250oC to1450oC. The sintered pellets at 1450oC achieved the highest dielectric constant of about7500. Properties comparison for this solid system with other studies is unable to performdue to lack of available literature in BST preparation from Ba(OH)z.8HzO-Sr(OH)z.8HzO-TiOz.In general, this project had achieved its objective to produce single phase BSTpellet by mechanical activation process with ultrafine particle size. The calcinationprocess is carried out at temperature as low as 500oC to decompose most (but not all) ofthe hydrated HzO. The dielectric properties obtained were within the expected range ofvalue for ultrafine particles.B) Project BackgroundIn the technology-driven global market today, electronic devices ranging fromcommon mobile phone, personal computers to sophisticated communication satelliteshave becom e part and parcel of our routine life. The performances of all these electronicdevices inevitably rely on the functional materials that are used to assemble them. Theongoing drive for electronic devices miniaturization has force the necessity to reduce thesize of these functional materials and also to discover better-performed materials.Therefore, the technological and economical significance of developing ultrafinefunctional materials without sacrificing too much of their electrical properties areenofmous.Bar-*Sr"TiOg is an important feroelectric-piezoelectric ceramic that has beenwidely used as dielectric materials in many electronic devices. The conventional methodof synthesizing Ba1-*Sr*TiO: involves mixing BaCO:, SrCO: & TiOz in stoichiometricratio, followed by high temperature (>1000"C) solid state reaction. Although this methodprovides a simple & straight forward synthesis route but it is often leads to compositionalinhomogeneous and particle coarsening. Several chemistry based method such as sol-gel,hydrotherm al and co-precipitation which are able to produce homogeneous and ultrafineBa1-*Sr*TiOr with certain heat treatment not exceeding 8000C. However, these methodsare often associated with the disadvantages such as very high manufacturing cost, lowproduction yield and bringing ecological problems, which make them unsuitable forindustrial scale production. Furthermore, most of them have yet to demonstrate anysignificant advantages over the conventional method'Mechanical activation technique is derived from mechanical alloying methodwhich develops for the production of composite powder, inter-metallic compound andamorphous metallic powder. It was later employed to synthesize various magnetic andpowder by mechanically activated the starting materials through high energy milling.Mechanical activation technique has been successfully devised by researchers tosynthesized single phase electronic ceramics powder. Although it is known that thetechnique works and so is useful, but it is not clearly understood than those thermallyactivated process. A number of research has been devoted to mechanical activationtechnique in recent years, there are still a number of problem to be address and eventuallysolved.The intrinsic advantage of mechanical activation method lies in its ability to effecta solid state reaction through mechanical treatment, instead of by calcining at a highenough temperature, easily exceeding 1000oC by conventional method. It can also leadsto an improvement in the reactivity of the starting materials and therefore the desiredceramic phase is formed at a lower calcination temperature. Mechanical activation is ableto change the thermodynamic potentials of reagents and diminish the temperatures of thechemical reaction. Mechanical activation which is a energy-intensive homogenizinggrinding process, helps to intensify transport of the reactants by intimate mixing of solidsubstances not only at the physical but also on a chemical level.The relatively ease of producing mechanical activation-derived powder in largequantities compared to other nonconventional synthesis technique will be the key drivingforces in propelling this process. Therefore, this technique shall be evaluated as analternative synthesis route or a value added step in Bar-*Sr*TiO3 powder preparation.C) Project Objectives. Lowering the synthesis temperature of Ba6 7516 sTiOl by mechanically activatingmixtures of Ba(OH)2. SHzO-Sr(OH)2. 8HzO-TiOz.r Improved physical properties and dielectric properties of the Bas.7Sro.:TiOrproducedD) Project Research ApProachThe processing of BST from Ba(OH)z.8HzO-Sr(OH)z.8HzO-TiO2 is shown infigure 1.Ba(OH)2. 8HzO-Sr(OH)2. SHzO-TiOzMechanical activationat 300 rpmMechanical activationfor 20.40 & 60 minsCalcination at500 & 6500cPelletizationSintering at 1250,1300, 1350 & 1450"CDielectric properties measutementFigure 1: Processing flow of BST derived from Ba(OH)z.8HzO-Sr(OH)z'8HzO-TiOzE) Project Result & DiscussionThe dielectric performance of BST40c0350030s0€ 2sooE 2ooo€ lsoo10*0500n1254 1300sinterlng ternp1350a20 =40 n3603?ff8ffi,fiFj/.szr.<.11effi t=-Effi:Figure 2: Dielectric constant value from sarnples derived from 500oC calcinationtemperature at different milling duration as well as sintering temperatureFigure 2 showed the correlation among dielectric value, milling duration (20,40and 60 mins) and sintering temperature. No significant evidence shown that longermilling time will enhance the dielectric constant performance. However, as for thesintering temperature, the is a significant increase of dielectric constant value byincreasing the sintering temperature.To further support the statement, we have increased the sintering temperature to1450oC. It shown in figure 3 that higher dielectric constant is achieved as the sinteringtemperature increased to 1450oC. This phenomenon can be explained by themicrostructure of the sintered pellets which is discussed later in this report. Sampleswhich sintered at 1450oC consistently showing better dielectric constant performance.Further increased of the sintering temperature is not attempted as higher sinteringtemperature will indueed phase changes in BST for liquidified sintering.*rt*.Lr'!{trl\t{)8fi0il?fi0CI60*ff50s0400{)3ff0il?000100flUffiffith 4finrilling durstion {minr}tr 1350 r{ 1450OUFigure 3: Dielectric constant composrison between samples sintered at l350oC and14500CThe phase analysis of sintered pelletsXRD phase analysis was performed to investigate any phase changes occurred at1450oC sintering which might lead to increased of the dielectric constant value. Figure 4showed the XRD pattern of both samples which sintered at I250oC and 1450oC, bothdiffractogram are similar indicating the presence of single phase BST. Hence, theincreased of dielectric value was not phase-change related. It is also proven that BSTphase are stable in the range of sinteing temperature of 1250oC to 1450oC.lcounts I4AB3BEzAA146E6I026lFigure 4: XRD for sample (A) sintered at l250oC and (B) sintered at 1450oCThe microstructure of the sintered pelletsThe microstructure of the sintered pellet had been investigated. Figure 5 showedthe microstructure of the sintered pellet at different temperature. Significant different ofmicrosctructure was observed, at I250oC the pellet is extremely porous. For samplesintered at 1300oC and 1350oC, relatively it is less porous however the particles are stillnot sintered properly. For sample sintered at 1450oC, a dense microstructure wasobserved with the grain size in the average of I pm. These significant changes ofmicrostructure against the sintering time explained the dielectric value difference shownin figure 2 and 3. A fully dense pellet will enhanced the dielectric properties. However,that is not the only factor that influenced the dielectric properties; other parameters suchas purity, sintered grain size, uniformity of the grain size etc. play a role in determiningthe dielectric properties as well.Pellet sintered at 1450oC shown in figure 5 (d) possessed wide range of grain size,this was due to the nature of planetary milling mechanism which commonly inducedcaking effect to the solid system, hence certain solid was intensively milled (espeacillythose have higher surface contact with milling media).(c)Figure 5 Microstructure of BST pellet samples sintered at (a)1350oC and (d) 1450oC(d)l250oc, (b) 1300"c, (c)The TEM morphology and phase analysis of calcined powderFigure 6: TEM powder morphology of the calcined powderFigure 6 showed the particle morphology of the calcined powder. Ultrafineparticle size are ranging from 100 to 300nm. However, most of the particles are highlyagglomerated after the mechanical acl:ation process due to the high energy impact fromthe milling media. The elongated particles are believed to be BaCOr and SrCOr based onour previous research on BaCOI-SrCO:-TiOz solid system studies. Phase analysis infigure 7 showed that dominant phase of BST was found, however there are remnant ofcarbonates phase in the mixture. This is in agreement with the TEM result which shownformation BaCOI as well as SICO3 in the calcined mixture. Formation of carbonates tookplace when the BaO and SrO (which is the resultant of decomposition of Ba(OH)z.8HzOand Sr(OH)2.8HzO) reacted with COz in air instead of TiOz, indirectly indicating that thesolid mixture was not able to homogenously mixed'lcounts lLzE166BE664A28s5* Barium Strontium Titanate A BaCO, #TiO2TO2B ]* srco:Figure 7: XRD diffractogram of calcined Ba(OH)z.8HzO-Sr(OH)2.8H2O-TiOz mixtureOverall DiscussionIn this studies, we had produced single phase BST pellet by applying calcinationtemperature as low as 500oC. The major challenge in applying mechanical activationtechnique to the solid system was to overcame the caking problem.The planetary milling mechanism is shown in figure 8, the powder is primarilycrushed by the high energy impact of grinding balls together with friction between theballs and the wall of the grinding bowl. The grinding balls and the powder in the grindingbowl are acted upon by the centrifugal forces due to the rotation of the grinding bowlabout its own axis and due to the rotating supporting disc. The grinding bowl and thesupporting disc rotate in opposite directions, so that the centrifugal forces alternately actin the same and opposite directions. This results in, as a frictional effect, the grindingballs running along the inner wall of the bowl, and as an impact effect, the ballsimpacting against the opposite wall of the grinding bowl. The impact effect is enhancedby the grinding balls impacting against one another.However, one of the drawbacks in this system is that the powder in the milling jaradhered to the milling jar as well as the rqilling balls; this phenomenon is referred ascaking. The caking problem increased when higher speed was applied in the planetarymilling resulting in hard caking which are difficult to scrap off from the milling jar.Caking problem caused immobility of the particles and thus restrained the mixing process.Figure 9 showed the photo of the mixture which is planetary milled. Afterplanetary milling minimum loose powder are found the bowl, majority of the solids are"caked" to the wall of the iar.Figure 8: Schematic planetary milling mechanismE&ffi4lEI4tle*bti:fitdffi,Hnri:.oruai ss{.{i{rnFigure 9: Powder caking after planetary millingCalcination at 500oC is the lowest that we can achieved in this study. Figure 10showed the comparison of the sintered pellets prepared from 400oC and 500oC calcinedmixture. The pellets prepared from 400oC calcined mixture cracked after sintering, this isdue to insufficient decomposition at 400oC. Further significant decompostion took placeduring sintering which caused the pellet to crack.(a) (b)Figure 10: Sintered pellets derived from mixture calcined at (a) 400oC and (b) 500oCThe dielectric properlies obtained in this studies are relatively low as compared tothose derived from conventional solid state reaction route. The dielectric properties aremost optimum in the grain size range of 2-5 pm, and subsequent declined if the grain sizeis smaller or bigger. Therefore ultrafine powder is expected to yield lower dielectric value,however it makes miniatwization possible which is crucial in electronic field.Figure 11 showed the grain size of 1300oC sintered pellets, it has a porousstructure with the grain size at the low end of submicron. Ultrafine particles derived frommechanical activation prone to form agglomeration due to their large surface area as wellas the caking effect. The agglomerates transformed into aggregates during calcinationprocess and therefore resulting in greater variance of the particle distribution, itminimized the numbers of contact points among the particles thus resulting in poorersinterability. Furthermore, the decomposition of the remnant phase of BaCO: and SrCOIin the calcined powder contributed to the porous microstructure; hence degraded thedielectric properties.Figure 1 1 : Microstructure of pellet sintered at 1 3 00oC

Synthesis Of Ultrafine Ba07 Sr0.3 TiO3 by Mechanically Activating Process.

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Synthesis Of Ultrafine Ba07 Sr0.3 TiO3 by Mechanically Activating Process.

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