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Effect OF LITHIUM FLUORIDE ON THE DIELECTRIC PROPERTIES OF BARIUM TITANATE

Effect OF LITHIUM FLUORIDE ON THE DIELECTRIC PROPERTIES OF BARIUM TITANATE. Laldja TAÏBI – BENZIADA (http://perso.usthb.dz/~lbenziada) Faculty of Chemistry , USTHB, Algiers , ALGERIA. IUPAC 9 th International Conference on Novel Materials and Synthesis (NMS – IX)

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Effect OF LITHIUM FLUORIDE ON THE DIELECTRIC PROPERTIES OF BARIUM TITANATE

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  1. Effect OF LITHIUM FLUORIDE ON THE DIELECTRIC PROPERTIES OF BARIUM TITANATE Laldja TAÏBI – BENZIADA (http://perso.usthb.dz/~lbenziada) Faculty of Chemistry, USTHB, Algiers, ALGERIA IUPAC 9th International Conference on NovelMaterials and Synthesis (NMS – IX) October17 – 22 , 2013, Shanghai, CHINA

  2. summary • Introduction • Experimentalprocedures • Results and discussion • Conclusion • References

  3. introduction

  4. Interest for materials • Materials have alwaysrepresented an essential aspect of human society. • Nowadays, the materialbecamesynonymouswithexistence for anyindustry. • In new technologies of informations and communications, the progress and successare closelylinked to the development of advancedceramicswithhigher and higher performances but alsowithlower and lowerfactorycost.

  5. Ceramicsproducts Conventionalceramics Microstructure Engineering ceramics

  6. Abo3relatedmaterials • Amongthese new technicalceramics, ABO3perovskites and theirsolid solutions are very attractive for microelectronicindustry. • With the devicesminiaturization, ATiO3 ceramicsbecame the key materials for the development of smart systemswithartificial intelligence. • Up to now, the variedPZT have dominated the market of microelectronic components. However, the toxicity of Pbis a seriousthreat to humanhealthand environment.

  7. Applications of Abo3 perovskites • Capacitors • Sensors • Resonators • Piezoelectricactuators • Pyroelectricinfrared detectors • Electro-opticalmodulators • Computer and mobile phone memories… FRAMs

  8. Computer’smemories T. Shiosaki, The recentprogress in the research and development for ferroelectric memory in Japan (1997)

  9. objectives • To lowerboth the sinteringtemperature (Tsint. ~ 1400 ° C) and the ferroelectric Curie temperature (TC = 120 ° C) of BaTiO3 ceramicsusingLiF as additive. • To reinvestigate the effect of lithium fluoride on dielectricpropertiesof BaTiO3 ceramicssintered in various conditions.

  10. BaTiO3 properties • Phase transitions : RhombohedralOrthorhombicTetragonalCubic • Ferroelectric Curie temperature : TC = 393 K • Relaxation frequency : fr= 500 MHz • Symmetryat room temperature: Tetragonal 193 K 278 K 393 K

  11. O Ti Ba BaTiO3 unit cellat 300 k a = 3.998 Å c = 4.018 Å

  12. Experimentalprocedures

  13. Samplespreparations • Barium titanate withvarious ratio BaO/TiO2waspreviouslysynthesized by calcination of BaCO3 and TiO2at1100 ° C: 0.97 BaCO3 + TiO20.97 BaTiO3 + 0.03 TiO2 + 0.97 CO2 (BT0 0.97) BaCO3+ TiO2 BaTiO3 + CO2(BT0 1.00) 1.03 BaCO3 + TiO2 BaTiO3+ 0.03 BaO + CO2 (BT0 1.03) • Severalchemical compositions werethenpreparedfrom the variedBTO and LiFthenwet-groundin ethanol : (1-x) wt. % BTO + x wt. % LiF • The powder mixtures were cold-pressed to pellets with an organic binder. The disksthusobtainedweresintered in various conditions.

  14. x BaCO3 + y TiO2 Grinding, Calcination 1100 °C x wt. % LiF BaTiO3+CO2 (1-x) % BaTiO3 + x % LiF Grinding Sintering(T °C) Ba(Ti, Li)(O, F)3

  15. Methods of investigations • X-ray diffraction analyzeswerecarried out at room temperature on crushedceramics in the 2 range 10 – 90 °. • Scanning Electron Microscopyobservations wereperformed on fracturedceramics. • Dielectricmeasurementswerecarried out under vacuum at 1 kHz between 180 K and 500 K. • Ceramicswereinvestigated by Auger microprobeand thermal analyses. • Chemical analyseswereperformed and fluorine and lithium losseswerecalculated.

  16. Results and discussion

  17. DRX spectra of BaTiO3 ceramicssinteredwith 2 wt. % LiF at 950 ° C for 2 h BTO (1.03) BTO (1.00) • The unit cellremainstetrago-nal for BTO(0.97). • The latticesymmetrybecomescubic for BTO (1.00)and BTO (1.03). BTO (0.97) 2  (°)

  18. Effect of BaO/TiO2 ratio on the permittivity of BaTiO3 ceramicssinteredwith 2 wt. % LiF at 950 ° C for 2 h • Excess of TiO2inhibits the sintering and’r. • Excessof BaOenhancesthe sintering and ’r. • The best dielectriccharacteristics are obtainedwithBTO (1.03)

  19. Effect of LiF amount on permittivityof BaTiO3 (1.00) ceramicssinteredat 950 ° C for 2 h •  ispractically constant. • TCdecreases and ’r increases. • The best dielectriccharacteristics are observedwith3 wt. % of LiF.

  20. Effect of LiF amount on permittivityof BaTiO3 (1.03) ceramicssinteredat 950 ° C for 2 h •  isverylow for 1 wt. % of LiF . • TCdecreases and ’r increases. • The best dielectriccharacteristics are obtainedwith3 wt. % of LiF.

  21. Effect of holding time on permittivityof BaTiO3 (1.00) ceramicssinteredwith 2 wt. % LiF at 950 ° C •  increasesslightly. • TCincreasesand ’r decreases. • The best dielectriccharacteris-tics are obtained for tsint. =2 h.

  22. Effect of holding time on permittivityof BaTiO3 (1.03) ceramicssinteredwith 2 wt. % LiF at 950 ° C •  increasesslightly. • TCincreasesand ’r decreases. • The best dielectriccharacteris-tics are obtained for tsint. =2 h.

  23. Effect of sinteringtemperature on permittivityof BaTiO3 (1.00) ceramicssinteredwith 2 wt. % LiF for 2 h •  increases. • TCdecreases and ’r increases. • The best dielectriccharacteristics are obtained for Tsint. =1100 ° C.

  24. Effect of sinteringtemperature on permittivityof BaTiO3 (1.03) ceramicssinteredwith 2 wt. % LiF for 2 h •  increases. • TCdecreases and ’r increasesthendecreases. • The best dielectriccharacteristics are obtained for Tsint. =950° C.

  25. Temperaturedependence of permittivity and losses for BaTiO3 (1.03) ceramicsinteredwith 2 wt. % LiF at 950 ° C for 2 h in free air

  26. Effect of sinteringatmosphere on permittivityof BaTiO3 (1.03) ceramicssinteredat 950 °C with2 wt. % LiF for 2 h • The best shrinkageand the bestdielectriccharacteris-tics are obtainedwhensinteringisperformed in free air.

  27. Temperaturedependence of permittivityof BaTiO3 (1.03) ceramicssinteredwith 2 wt. % LiF in various conditions • The bestdielectriccharacteris-tics are obtainedwhensinteringisperformedat950 °C for 2 h in free airthenat1200 °C in sealed tube for 2 h.

  28. Chemical composition, fluorine and lithium losses of BTO (1.03) ceramicssinteredwith 2 wt. % LiF for 2 h atvarioustemperatures • Li and F lossesincreasewithincreasing the sinteringtemperature. Lilosses are more important thanthose of F.

  29. DTA and TG thermograms of 98 wt. % BTO (1.03) + 2 wt. % LiF • The exothermicpeakat280 °C isprobably due to the hydrolysis of LiF: LiF + H2O LiOH + HF • The endothermicpeakataround630 °C isascribed to Liand Flosses. • The weightlossreaches50 % afterheatingat950 °C for 2 h. 280 °C DTA 630 °C TG

  30. Micrographs of ceramicssinteredat 850 or 950 °C 950°C 98 wt. % BTO (1.03) + 2 wt. % LiF 98 wt. % BTO (1.03) + 2 wt. % LiF 850°C • The grain size increases and the porositydecreaseswithincreasing the sinteringtemperature.

  31. Auger spectra of BaTiO3 (1.03) fracturedceramicssinteredwith 2 wt. % LiF at950 ° C for 2 h Beforesputtering Aftersputtering • Ba, Li, O, Tiand Felements are detected and a composition gradientisobserved in the grains.

  32. conclusion

  33. The effect of LiF on dielectricproperties of BaTiO3withdifferent ratio BaO/TiO2and sintered in various conditions has been reinvestigated. • As result, an excess of TiO2inhibits the sinteringprocess and the permittivity. On the other hand,BaOexcessenhancesboth the densification and the dielectriccharacteristics. The best densification isobtainedwithBTO (1.03). • The addition of LiF to BTO (1.00) or BTO (1.03) lowerssimultaneously the sintering and the ferroelectric Curie temperatures. • BTO (1.00) or BTO (1.03) ceramics display rounded and broad maxima due to composition gradient in the grains. • The ceramics of BTO (1.03) sinteredwith2 wt. % of LiFat950 ° C for 2 h couldbeused for Z5Umultilayercapacitorsmanufacturing.

  34. Norms of type ii class z5u capacitors 98 wt. % BTO (1.03) + 2 wt. % LiF, 950 °C, 2 h • Ferroelectricdielectric • 5000 ’r (293K)  9000 • ’r(T) - ’r (293K) / ’r (293K) = + 22 % at283 K • ’r (T) - ’r (293K) / ’r (293K) = - 56 %at356 K • Tan (293K)  2.5 % + 22 % Z5U - 56 %

  35. references

  36. [1] J. M. Haussonne, G. Desgardin, PH. Bajolet, B. Raveau, JACS, 1983, 66 (11): 801. • [2] L. Benziada, Thèse de doctorat, 1987. • [3] S-F. Wang, K-C. Cheng, Journal of the Chinese Institute of Engineers, 1999, 22(1): 61. • [4] S-F. Wang, T.C.K. Yang, W. Huebner, J.P. Chu, J. Mater. Res., 2000, 15(2):407. • [5] L. Zhang, J. Zhai, X. Yao, ferroelectrics, 2009, 384: 153. • [6] H. Naghib-zadeh, C. Glitzky, I. Dörfel, T. Rabe, JECS, 2010, 30: 81. • [7] G. Liu, Y. Jiang, T.W. Button, Ferroelectrics, 2011, 421: 72.

  37. THANK YOU FOR YOUR ATTENTION PEACE WORLDWIDE

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