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Sep. 30                              IJASCSE, Vol1 Issue 2, 2012     Low Temperature Synthesis of Ba3Ta2ZnO9 (BZT) and Ba3...
Sep. 30                               IJASCSE, Vol1 Issue 2, 2012                                                       fo...
Sep. 30                               IJASCSE, Vol1 Issue 2, 2012     mixture of                                        to...
Sep. 30                               IJASCSE, Vol1 Issue 2, 2012                                                         ...
Sep. 30                                                                   IJASCSE, Vol1 Issue 2, 2012                     ...
Sep. 30                                                                           IJASCSE, Vol1 Issue 2, 2012perature arou...
Sep. 30                                                                                          IJASCSE, Vol1 Issue 2, 20...
Sep. 30                            IJASCSE, Vol1 Issue 2, 2012                                                    Formatio...
Sep. 30                               IJASCSE, Vol1 Issue 2, 2012Director, College of Engineering, Pune.Namrata Saraf and ...
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Low Temperature Synthesis of Ba3Ta2ZnO9 (BZT) and Ba3Nb2ZnO9 (BZN) by Wet Chemical Route


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Powders of high microwave dielectric material Barium Zinc Tantalate (BZT) and Barium Zinc Niobate (BZN) have been prepared by wet chemical procedure at moderately low temperature ~5000C. Co-precipitate and mechanical mixtures of hydroxide of Ba(II), Ta(V)/Nb(V) & Zn(II) in 3:2:1 mole proportion on thermal decomposition, showed formation of the desired perovskite phase at 5000C. The product of co-precipitate and mechanical mixture of hydroxides heated upto7400C produced single phase BZT. Thermal decomposition of mixture was studied in static air atmosphere by TG & DTA. XRD studies on a sample heated to 500, 740, 780 & 9000C confirmed the formation of single phase BZT formation at 7400C and that of BZN at7800C.

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Low Temperature Synthesis of Ba3Ta2ZnO9 (BZT) and Ba3Nb2ZnO9 (BZN) by Wet Chemical Route

  1. 1. Sep. 30 IJASCSE, Vol1 Issue 2, 2012 Low Temperature Synthesis of Ba3Ta2ZnO9 (BZT) and Ba3Nb2ZnO9 (BZN) by Wet Chemical Route Namrata Saraf, Manisha Khaladkar, Imtiaz Mulla Rajashree Kashalkar, Department of Applied Science Emeritus Scientist(CSIR) Department of Chemistry, College of Engineering, Pune CMET, Pune India S.P.College, Pune India Pune IndiaAbstract: found applications as small electronic component for use in hand heldPowders of high microwave dielectric communication device like cellular phone.material Barium Zinc Tantalate (BZT) and Miniaturization of electronic devices andBarium Zinc Niobate (BZN) have been adding more functionalities have given rise toprepared by wet chemical procedure at a need for small size microwave resonatorsmoderately low temperature ~5000C. Co- with good frequency selectivity and highprecipitate and mechanical mixtures of temperature stability. Since the discovery ofhydroxide of Ba(II), Ta(V)/Nb(V) & Zn(II) in excellent microwave dielectric properties3:2:1 mole proportion on thermal exhibited by Ba(Zn1/3Nb2/3)O3 anddecomposition, showed formation of the Ba(Zn1/3Ta2/3)O3 ceramics with perovskitedesired perovskite phase at 5000C. The structure. Many researchers [1-12] haveproduct of co-precipitate and mechanical prepared the material and there are severalmixture of hydroxides heated upto7400C patents on preparation of BZT [13].produced single phase BZT. Thermaldecomposition of mixture was studied in Most of these procedures utilize oxides ofstatic air atmosphere by TG & DTA. XRD Ba, Ta/Nb, Mg/Zn in 3:2:1 mole proportion.studies on a sample heated to 500, 740, 780 Although the material is used by many& 9000C confirmed the formation of single workers; the reports in print are very few andphase BZT formation at 7400C and that of especially reports on wet chemical route forBZN at7800C. synthesis are rare except for work done by Maclaren et al. [9], they have used bariumKey words: BZT, BZN, DTA, TG, XRD, acetate, zinc acetate, tantalum oxalate anddielectric ceramics, Wet chemical route. Ganguly et al. [8] have used Mg(NO3)2.6H2O for the formation of Magnesium Niobate I. Introduction: (MN) and Magnesium Tantalate (MT). More popular route for preparation of BZT is solidMixed metal oxide ceramics with Perovskite state route, where stoichiometric amounts of(ABO3) structure are of great importance for corresponding oxides viz. 3BaO, ZnO,various electronic applications. Among this Ta2O5/Nb2O5 are mixed, milled togetherfamily BZT and BZN are very significant manually or using ball-mill and heated atmembers because of their high dielectric temperature of about 13000C [11-14] for fewconstant, low loss factor at resonant hours.frequency and near zero temperaturecoefficients at resonant frequency. BZT has 1|Page
  2. 2. Sep. 30 IJASCSE, Vol1 Issue 2, 2012 for studying the decomposition. Thermo- gravimetric Analysis (TG) was employed toThe main problem associated with high study the decomposition. After plotting thetemperature (above 13000C) sintering is weight loss curves as a function ofvolatility of ZnO. This leads to non- temperature few temperatures were selectedhomogeneity in ZnO concentration is and the precursors were heated to thoseobserved on the surface and in the bulk. temperatures. The XRD analyses of theHigh temperature sintering results in above heated samples were carried out toformation of undesirable binary oxide barium monitor various products formed at the pre-tantalate. Naturally the ZnO deficient phase decided temperatures. The experimentationdoes not have desired dielectric constant is divided into three parts:and hence device application fails. To 1) TG and DTA measurements were carriedeliminate the problem, sintering temperature out using equipments fabricated in house,must be kept below 13000C. This is possible the decomposition were studied in static airwhen powders are synthesized by wet atmosphere using heating rate of 100C /min,chemical route [8]. Such chemically from ambient to 10000C, TG plots are shownsynthesized powders possess fine particle in figures 1to 4and DTA are shown in Fig 5size distribution and low aspect ratio particle and 6.morphology, as well as better homogeneity 2) Mixtures were heated up to 500, 740,in micro-structure and chemical constitution 9000C and soaked for 1hr at the final[1,2]. The resultant powder possesses better temperature. The products thus obtainedsintering ability. Hence wet chemical were analyzed by Bruker AXS D8 Advance Xsynthesis is a promising route. ray diffractometer in 2θ range 20- 800. 3) Surface morphology was recorded onIn wet chemical method precursors are JEOL JSM 6360A Scanning Electronadded to give either mechanical mixtures or of metal salts in desired moleproportion. Precipitate filtration, drying and List of samples studied is given below:calcinations of dried precursor was carriedout. The dried precursors were then heated Table-1 Samples under constant pre decided rate. We havesuccessfully synthesized Barium Zinc Sr Precursor Sam RawNiobate (BZN), Barium-zinc-tantalate (BZT), N sample ple materialZinc tantalate, Magnesium tantalate, Zinc o. abbrNiobate by wet chemical route [1,2]. This eviatpaper reports results on synthesis of single ionphase BZT and BZN using wet chemical 1. Binary mixture ZT Ta2O5 &route at temperature as low as 7400C. of Tantalum & (cp) Zn (NO3)2 zinc II. Experimentation: in 2:1 mole proportion asCo-precipitated hydroxides of Ba, Zn, Ta/Nb co-precipitate.were prepared in 1:2:3 mole proportion and 2. Binary ZT Ta(OH)5 &subjected to heating from ambient to 10000C mechanical (mm) Zn(OH)2 2|Page
  3. 3. Sep. 30 IJASCSE, Vol1 Issue 2, 2012 mixture of to the binary co-precipitate prepared by Tantalum and method given above. zinc In 2:13. Barium, BZT Ba(OH)2 & b) Mechanical mixtures (mm): Tantalum and (cp) ZT zinc 3:2:1 hydroxide In case of Mechanical mixtures individual (cp) hydroxides were prepared from raw materials as given in the flowchart No.1 and4. Barium, BZT Ba(OH)2,T ammonium hydroxide was used as Tantalum & (mm) a(OH)5 & precipitating agent. The resultant precipitates zinc in 3:2:1 Zn(OH)2 were washed with distilled water till the pH of5. Niobium & ZN(c Nb2O5 & filtrate was 7, and the precipitate was zinc, 2:1 p) Zn (NO3)2 subjected to drying at 1100C for 5hr. The6. Niobium & zinc ZN Nb(OH)5 & dried samples were mixed in required 2:1 (mm) Zn(OH)2 proportion (3:2:1 Ba: Ta: Zn) in agate mortar7. Barium, BZN Ba(OH)2 & for 2 hrs and stored in vacuum desiccators. Niobium & (cp) ZN zinc, 3:1:2 hydroxide III. Results and Discussion: (cp)8. Barium, BZN Ba(OH)2,N It is observed that precipitate washing, Niobium & zinc (mm) b(OH)5 & filtration and drying temperature play , 3:1:2 Zn(OH)2 significant role in deciding the homogeneity, and phase formation temperature of BZT andPreparation of hydroxide mixtures: BZN. TG interpretation a) Co-precipitation method (cp): ZT(cp) ZT(mm) 0 5The procedure was chosen from earlier 10 % weight lossreports by Ravi et al [1, 2] for preparation of 15 20Mg4Ta2O9, MgNb2O6 etc. The major step is 25dissolution of Ta2O5 and Nb2O5. It was 30carries in fuming chamber using Teflon 35 0 200 400 600 0 800 1000 temperature Cbeaker on a water bath. The beaker wasfitted with long air condenser. 20 hours Fig.1 Decomposition pattern of co-precipitatedigestion time was required for Ta2O5 and 8 ZT (cp) and ZT mm –hydroxidehours for Nb2O5. After the dissolutionrequired amount of Zinc nitrate was added As can be seen from above figureas solution and precipitation was carried out decomposition of cp starts and completes atusing ammonium hydroxide solution till the lower temperature. The actual weight losspH reached 9. Voluminous white precipitate steps and reactions are given below.was obtained. Filtration, washing and drying For cp ZnTa2(OH)12.2NH4OH ZnTa2O6was carried out. For preparation of ternary For mm Zn (OH)2 +2 Taco-precipitate Barium hydroxide was added (OH).2NH4OHZnTa2O6 3|Page
  4. 4. Sep. 30 IJASCSE, Vol1 Issue 2, 2012 400 69 H2O Ta- Tem % Decom Residual intermedi perat weig positio compound ate ure ht n 400- 5.3 2.08 ZnTa2O6 o C loss product 800 6 H2OBZ 55- 12.98 -11.8 Partly BZT (cp)T 260 H2O dried 0 BZT (mm)cp presursor. 10 260- 20.19 -14.11 ZnTa2(OH % weight loss 20 400 H2O, )12 + 30 2 2BaO+ NH4OH 1 Ba(OH)2 40 400- 9.61 -7 H2O 3Ba2TaZn 50 0 200 400 temperature 0 600 C 800 1000 800 1from O9 (cp) Ba, hydroxide Fig.2 Decomposition pattern of co-precipitate 6from BZT (cp) and BZT mm –hydroxide For cp Ta + ZnTa2 (OH)12.2NH4OH Zn cp +3Ba(OH)2Ba3ZnTa2O9BZ 80- 4.77 -3H2O Amorphou For mmT 180 (2from s Ba(OH)2.8H2O+Zn(OH)2+2Ta(OH)5Ba3ZnTmm Zn and precursor a2O9 1from Ta/Ba) 190- 5.53 -3.5 ZnO ZN (mm) 290 H2O 0 ZN (cp) 300- 3.15 -2 H2O Ba3Ta2Zn 10 730 O9 20 % wt loss 30 40Sr. Tem % Decomp Residual 50No perat wt osition compoun 60 0 200 400 600 800 1000 ure los product d Temperature 0 C o C sZT 115- 16. -2 partial Fig.3 Decomposition of co-precipitate ZN(cp)cp 245 77 NH4OH Ammonia and ZN (mm) hydroxide ZnNb(OH)7  -2 H2O expulsion ZnNb2O6 & Decomposition reactions for mm Zn(OH)2+ decompo Nb(OH)5.7H2O.(1H2O,1 NH4OH) ZnNb2O6 sition 255- 25. -4H2O ZnTa2O6 455 81 Decomposition reactions for cpZT 55- 10. 2 NH4OHm 260 37 NH4OH Free ZTm 260- 10. 4.15 ZnO + 4|Page
  5. 5. Sep. 30 IJASCSE, Vol1 Issue 2, 2012 Temp % Decom Residual eratur W positio compound e loss n adsorbed water, absorbed water, ammonia produc water of crystallization and water released t due to decomposition of hydroxide respectively. The DTA plots obtained forBZ 100- 14.2 -10.82 Dehydrated various samples are shown in Fig 5 and 6N 200 1 H2O BZN (cp) below. The decomposition pattern of ZT mmcp 273- 14.7 -11.23 Anhydrous & cp are almost identical. ZT mm 530 6 H2O BZN (cp) decomposition occurs in 55 to 350 and 350 560- 12 -9.1 BZN (cp) to 6000C in two steps and in ZT cp occurs in 660 H2O oxide four steps. Desorption, dehydration &BZ 100- 7.24 - 5.5 Dehydrated decomposition are all endothermic reactions.N 290 H2O BZN mm In all the four DTA samples a sharpmm 350- 26.9 -21.6 BZN mm endothermic peak is observed at around 400 4 H2O anhydrous 3900C which is assigned to decomposition of 575- 7.65 -5.8 BZN mm ZT hydroxide. 695 H2O oxide BZN (cp) Tem % Deco Residual 0 BZN (mm) pera W mpos compound ture loss ition 10 0 C produ % weight loss 20 ct 30 ZN 155- 16.7 -5 Dehydrate cp 225 5 H2O d ZN 40 50 0 200 400 temperature in 600 0 C 800 1000 225- 6.04 -1.8 Anhydrous 305 H2O ZN 435- 9.36 - 2.85 ZN oxideFig.4 Decomposition pattern of co-precipitate 685 H2OBZN (cp) and BZN mm –hydroxide ZN 55- 10.3 -1 DesorptionFor cp m 155 8 NH4O ofBa (OH)2.8 H2O+ ZnNb(OH)7 Ba3ZnNb2O9 m H 1ammoniaFor mm -1 & waterBa (OH)2.8 H2O+Zn(OH)2 + 2Nb(OH)5  H2OBa3ZnNb2O9 155- 21.5 - 3.5 Dehydratio 295 4 H2O n c) DTA interpretation: 357- 8.72 2.66 Completion 435 H2O of DTA measurements were carried out on dehydratioDTA instrument fabricated in house. The n&decompositions sequence was studied in decomposistatic air atmosphere using heating rate of At tion of Zn100C /min, from ambient to 9000C. The high 500- 6.02 2 Formationexothermic and endothermic peaks observed er 875 H2O of binaryin DTA plots were assigned to the loss of tem oxide of Zn-Nb 5|Page
  6. 6. Sep. 30 IJASCSE, Vol1 Issue 2, 2012perature around 660-670 0C co-precipitate 0.20shows a small exothermic peak & mm shows 0.15 0.10small endothermic peak which is little ZN mm 0.05 0.00conflicting but at temperature up to7500C -0.05 -0.10shows same reversal reaction enthalpies. It -0.15 0.4shows different stabilities of binary oxides 0.2formed which lead us to select co- 0.0 ZN cp -0.2precipitated product over mechanical mixture -0.4as starting material for ternary oxides. In -0.6 -0.8DTA of BZT a broad endothermic peak 0.4observed due to large amount of water of 0.2 0.0 BZN mmcrystallization at 100 for co-precipitate and at -0.2 -0.41400C for mechanical mixture. -0.6 -0.8 1For BZN mm closely separated endothermicpeaks due to release of large amount of 0 BZN cpassociated water. In cp single endothermic -1peak due to close association of molecules is -2observed. 0 100 200 300 400 500 600 700 800 0 Temperature C 0.10 0.08 0.06 0.04 0.02 Fig. 6 DTA plots of ZN, BZN (cp, mm) ZT mm 0.00 -0.02 -0.04 -0.06 -0.08 -0.10 0.10 0.05 0.00 ZT cp -0.05 -0.10 d) XRD studies: -0.15 0.2 0.1 Conformation of the phases formed at 0.0 various stages of decomposition was done BZT mm -0.1 -0.2 -0.3 -0.4 by XRD. XRD patterns recorded for mechanical mixture of BZT – hydroxides 0.2 0.0 -0.2 BZT cp heated up to 500, 7400C and on another -0.4 -0.6 -0.8 0 100 200 300 400 Temperature 500 0 C 600 700 800 sample heated up to 9800C for 2 hrs are shown in Fig 7-9. It can be easily seen that the sample heated to 5000C shows very poor Fig 5 DTA plots of ZT, BZT (cp, mm) crystallinity whereas the sample heated at 7400C shows single phase BZT, on heating the sample up to 9000C the crystallinity reduces and very low intensity peaks are observed corresponding to BZT phase. The XRD patterns were recorded for ternary hydroxide Ba Zn Nb heated up to and heated at 7400C for one hour. Fig 4 c shows the XRD patterns for mm, cp and solid state mixture of Ba, Zn and Nb oxides in 3:2:1 mole proportion. Comparison of the patterns 6|Page
  7. 7. Sep. 30 IJASCSE, Vol1 Issue 2, 2012reveal that BZN cp mixture heated at 7400Cfor one hr gives single phase BZN compoundas reported by C. T. Lee [14] where as thesolid state mixture shows binary oxides ZN inaddition to BZN . This indicates that for solidstate oxide mixture 7400C temperatures isnot sufficient for the formation of singlephase ternary BZN oxide. 900 C 0 740 C 0 2θ Fig. 9 XRD of BZN cp, mm , ss heated to 7400C 500 C 0 e) SEM Studies: Fig 10 a, b show SEM images of sintered 20 30 40 50 60 70 80 BZT powder and The SEM image shows regions of about 1 micron size rods withFig. 7 XRD of BZT heated to various uniform size and shape.temperatures 0 BZT mm at 740 C 0 BZT cp at 740 C Intensity Fig.10 a SEM image of BZT 20 30 40 50 60 70 80 2 thetaFig. 8 XRD for BZT cp & mm heated to7400C 7|Page
  8. 8. Sep. 30 IJASCSE, Vol1 Issue 2, 2012 Formation of ZT occurs at Temperature as low as 6800C for cp and single phase ZT oxide is formed at 7400C for mm. Formation of single phase BZT occurs at temperature below 7400C and the crystalline single phase disintegrates at temperatures around 9000C as can be seen from Fig. 7, the decomposition product of co-precipitateFig.10 b SEM image of BZT has better crystallinity; as compared to that of mechanical mixture. No high temperature sintering is required for the formation of single phase BZT if hydroxide route is adopted. Decomposition of ZT is complete at 740 but complete decomposition of ZN/BZN requires temperature more than 8400C.Sintering time of 1 hr. at 7400C for BZN & 1 hr at 8800C forFig. 10 (c) SEM image of BZN mm BZT is sufficient. In case of BZN cp and mm (Fig. 10 c and d) it was observed in mm sample there are two type of grains a needle like which is in majority and flat plates in lesser concentration. SEM image of cp sample shows a single grain type which more homogeneous hence it appears to better than mm.Fig. 10 (d) SEM image of BZN cp SEM images showed formation of uniform rods with plumbite structure having 1micron IV. Conclusions: size, on further magnification of a crystal lump similar rod like structure is observedWet chemical route is better suited for within the lump. The high dielectric constantpreparation of binary and ternary oxides of of the material appears to be due to fractalityZinc Tantalate and Barium Zinc Tantalate as observed in the crystal structure.compared to Solid state route.All hydroxides mixture cp as well as mmseem to have high tendency to adsorb V. Acknowledgements:ammonia as well as water. This Ammonia M.Y. Khaladkar and Namrata Saraf areand water is deeply embedded in the systemand require higher temperature (2600C for thankful to ISRO UoP STC, Pune andZN mm) for removal. Satellite application Centre (SAC) Ahmadabad for their financial and technical support. They are also thankful to the 8|Page
  9. 9. Sep. 30 IJASCSE, Vol1 Issue 2, 2012Director, College of Engineering, Pune.Namrata Saraf and R V Kashalkar are [11] H. Matsumoto, H. Tamura, K. Wakino,thankful to Principal S.P.College for his Jpn. J. Appl. Phy, (1991), vol. 30, pp.2347.timely help and encouragement for research [12] X. M. Chen, Y. Suzuki, N. Sato, I.S. Mulla is grateful to CSIR for Mater. Sci. Mater. Electron, (1994), vol.5,awarding Emeritus Scientist scheme. pp.244.VI. References: [13] M. Furuya, A. Ochi, J. J. Appl. Phys, (1994), vol. 33, pp.5482.[1] A. B Gaikwad, C. Navale, V. Samual, V.Murugan, V. Ravi, Mater. Res. Bull. vol [14] C. Lee, L. Chang, H. Yuen, S U Che, Y41(2006), pp.347-353. H Li, J. Am. Ceram. Soc, (2007) vol.90, pp. 483-486[2] V V Deshpande, M M Patil,S C Navale , VRavi Bull,Mater.Sci.(2005), vol .28, pp.205-207[3] S.C. Navale, V. Ravi, Mat. Sci. Eng.B,(2005), vol 119, pp.189-191.[4]H. Zhang, L. Fang, T. Huang, R. Yuan, J.Mater. Sci. (2004), vol 15, pp.695-69[5] M. Bieringer, S. M. Moussa, L. D.Noailles, A. Burrows, C. Kiely, M.JRosseinsky, R. M. Ibberson. Chem. Mater.2003, vol 15(2), pp.586-597.[6] C.Ferrari, A. Hernandes, J. Eu. Ceram.Soc, (2002), vol 22, pp.2101-2105.[7] B. Ahn, N. Kim, J. Mater Sci, (2002),vol.37, pp.4697.[8] M Thirumal, A K Ganguly, Mater. Res.Bull,(2001), vol .36, pp. 2421.[9] I MacLaren, S. Wannakukorale, C.Ponton, J. Mater. Chem, (1999), vol. 9,pp.2663.[10]K. Matsumoto, T. Hiuga, K.Takada, H.Ichimura, IEEE. Trans. UFFC, (1986), vol.33, pp.802. 9|Page