DIELECTRIC PROPERTIES OF ATiO3 CERAMICS ( A= Ca,Sr , Ba) SINTERED WITH 5 Mol. % OF LiF AND CaF2

1. DIELECTRIC PROPERTIES OF ATiO3 CERAMICS ( A=Ca,Sr, Ba) SINTERED WITH 5 Mol. % OF LiF AND CaF2 L . Taïbi - Benziada ; Y. Sedkaoui Algeria AMOMEN ’2011, October 27 - 29 2011, Kenitra, MAROCCO

2. SUMMARY INTRODUCTION EXPERIMENTAL PROCEDURES RESULTS AND DISCUSSION CONCLUSION

3. INTRODUCTION

4. INTEREST FOR MATERIALS Materials have always represented an essential aspect of Human Society . Nowadays, the Material became synonymous with Existence for anyIndustry . In new Technologies of informations and commu-nications, the Progress and Success are closely linked to the development of Advanced Ceramics with higher and higher performances but also with lower and lower factory cost to be competi-tive on the huge market of microelectronics .

5. APPLICATIONS OF CERAMICS Conventional Ceramics Engineering Ceramics Microstructure

6. ABO3 RELATED MATERIALS Among these new technical ceramics, ABO3perovskites and their solid solid solutions are of great interest for the Microelectronic Industry . With the devices miniaturization, ATiO3 ceramics became the key materials for the devevopment of smartsystems with high level of intelligence . Up to now, the varied PZT have dominated the market of microelectronic components. However, thetoxicity of Pb is a serious threat to human health and environment .

7. APPLICATIONS OF ABO3 PEROVSKITES Capacitors Sensors Resonators Piezoelectric actuators Pyroelectric infrared detectors Electro-optical modulators Computer memories... FRAMS

8. DRAMS FRAMS HDD T. Shiosaki, The recent progress in the research and development for ferroelectric memory in Japan (1997)

9. OBJECTIVES The sintering at low temperature of lead free ceramics related to ATiO3( A = Ca, Sr, Ba ) with the aid of 5 mol. % of CaF2andLiF : 0.95 ATiO3 + 0.05 CaF2 + 0.05 LiF The investigation of the dielectric properties in the obtained samples .

10. PROPERTIES OF ATiO3 CERAMICS ( A=Ca,Sr, Ba)

11. Calcium Titanate CaTiO3 Ferroelectric perovskite : TC ~105 K Phase Transitions Orthorhombic Tetragonal Cubic Pbnm I4/mcmPm3m Quantum Paraelectric Symmetry at room temperature Orthorhombic : a= 5.443 Å ; b = 7.653 Å ; c= 5.376 Å 1498 K 1634 K

12. Strontium Titanate SrTiO3 65 K 110 K • Phase Transitions Orthorhombic Tetragonal Cubic • Resonance Frequencies fr1= 3 x 1012Hz fr2 = 1.65 x 1013 Hz • Quantum Paraelectric or incipient ferroelectric • Symmetry at 300 K Cubic ( Pm3m) a = 3.905 Å

13. Barium Titanate BaTiO3 Ferroelectric perovskite : TC ~393 K Phase Transitions Rhombohedral Orthorhombic R3m Amm2 Tetragonal Cubic P4mm Pm3m Relaxation Frequency : fr ~ 500 MHz Symmetry at room temperature Tetragonal : a= 3.992 Å b= 4.036 Å 183 K 268 K 393 K

14. EXPERIMENTAL PROCEDURES

15. SAMPLES PREPARATIONS (1) ACO3 , TiO2 , CaF2 and LiFwerepre-heatedat150 °C to eliminatemoisture and to avoidanyhydrolysisduring the sinteringprocess. Stoichiometric titanates ATiO3werethensynthesized by calcination in air : ACO3 + TiO2ATiO3+ CO2

16. SAMPLES PREPARATIONS (2) Various chemical compositions were prepared and ground in ethanol : 0.95 ATiO3 + 0.05 CaF2 + 0.05 LiF The mixtures thus obtained were cold-pressed to pellets with a binder under a pressure of 100 MPa and sintered in air at 1000 °C for 2 h on zircona plates.

17. ACO3+TiO2 Grinding, Calcination 5 % ( CaF2+LiF ) ATiO3+CO2 Grinding Sintering 1000 °C , 2 h A0.95 Ca0.05 ( Ti0.95Li0.05 )O2.85 F0.15

18. METHODS OF INVESTIGATIONS The purity and the symmetrywerechecked by X-Ray diffraction on crushedceramicsat300 K . The ceramic’s microstructures wereobserved by Scanning Electron Microscopy on fracturedsamples . Dielectricmeasurementswerecarried out as a function of temperature ( 100 K - 550 K ) and frequency ( 102Hz- 4x106Hz).

19. RESULTS AND DISCUSSION

20. X-RAY DIFFRACTION The X-Ray peaks of CTO oxyfluoride are indexed in an orthorhombiccell. The XRD peaks of fluorinated STO are indexed in an orthorhombic multiple cell. The parametersof the orthorhombiccellare related to that of STO : ao ~ (2)1/2ac ; bo ~ 4 ac ; co ~ (2)1/2ac The XRD peaks of BTO oxyfluorideare indexed in a cubiccell.

21. Unit CellParameters

22. SEM OBSERVATIONS The micrograhs of A(Ti,Li)(O,F)3ceramics are monophasic. ATiO3ceramics are verybrittle( ΔΦ/Φ < 3 %)and porouswhereas the fluoridatedceramics are compact and veryhard ( 13 % ΔΦ/Φ  22 %) . The fluoride mixture CaF2 + LiFplays a double role: - as substituant and - as sintering agent .

23. Micrographs of CaTiO3 and CaTi0.95Li0.05O2.85F0.15  = 21.9 %  = 2.1 % CaTi0.95Li0.05O2.85F0.75 CaTiO3

24. Micrographs of SrTiO3 and Sr0.95Ca0.05Ti0.95Li0.05O2.85F0.15  = 1.1 %  = 18.7 % SrTiO3 Sr0.95Ca0.05Ti0.95Li0.05O2.85F0.85

25. Micrograph of Ba0.95Ca0.05Ti0.95Li0.05O2.85F0.15  = 13.5 % Ba0.95Ca0.05Ti0.95Li0.05O2.85F0.85

26. DIELECTRIC PROPERTIES OF A(Ti,Li)(O,F)3 CERAMICS

27. Temperature dependence of ε’r for CaTi0.95Li0.05O2.85F0.15 ceramic 102 Hz ε'r 5x102 Hz 103 Hz 5x103 Hz 104 Hz 5x104 Hz T (K) 105 Hz 2x105 Hz • A phase transition is detected around 283 K . • The quantum paraelectricbehaviour of CaTiO3disappears.

28. Temperature dependence of ε’’r for CaTi0.95Li0.05O2.85F0.15 ceramic • ε"rexhibits a frequency dependent peak around 283 K . 102 Hz ε"r 5x102 Hz 103 Hz 5x103 Hz 104 Hz 5x104 Hz T (K) 105 Hz 2x105 Hz • Below 250 K , the frequency dispersion is negligible

29. Frequency dependence of ε’r and ε’’r for CaTi0.95Li0.05O2.85F0.15 ceramic • The real permittivityε’ r is nearly constant (~80 ) . • In the opposite, the imaginary component ε"rexhibits a broadminimum at4.5 MHz .

30. Temperaturedependence of ε’r for Sr0.95Ca0.05Ti0.95Li0.05O2.85F0.15ceramic 102 Hz 5x102 Hz 103 Hz 5x103 Hz 104 Hz 5x104 Hz 105 Hz 2x105 Hz • Contrariwise to CTO , the quantum paraelectricbehaviour of STOstillpersists . • No phase transitionisdetected .

31. Temperature dependence of ε’’r for Sr0.95Ca0.05Ti0.95Li0.05O2.85F0.15 ceramic 102 Hz 5x102 Hz 103 Hz 5x103 Hz 104 Hz 5x104 Hz 105 Hz 2x105 Hz The increasein ε'rand ε" r beyond 400 K is ascribed to the electrical conductivity of lithium ion Li+ .

32. Frequency dependence of ε’r and ε’’r for Sr0.95Ca0.05Ti0.95Li0.05O2.85F0.15 ceramic at 300 K • The real permittivityε’ r is practically constant (~180 ). • In the opposite, the imaginary component ε"rexhibits a broadminimum at5 .6 MHz .

33. Temperature dependence of ε’r for Ba0.95Ca0.05Ti0.95Li0.05O2.85F0.15 ceramic A diffuse phase transition isdepictedat the ferroelectric Curie temperature T c ~ 293 K.

34. Temperature dependence of tanδ for Ba0.95Ca0.05Ti0.95Li0.05O2.85F0.15 ceramic The permittivitybroadpeakisassociated to a minimumof the losses.

35. Frequency dependence of ε’r and ε’’r for Ba0.95Ca0.05Ti0.95Li0.05O2.85F0.15 ceramic at 300 K 4000 ε'r 3000 2000 2 1000 ε"r 5 7 6 8 log f (Hz) The complexpermittivityexhibits a dielectricrelaxation around10 MHz.

36. CONCLUSION

37. ATiO3 ceramics ( A = Ca, Sr, Ba ) were sintered at low temperature with the aid of 5 mol.% of LiF+CaF2 The oxyfluoride deriving from CTO exhibits a peak of ε‘ r and ε"raround 283 K . For STO, no phase transition is detected in the temperature range investigated. The ceramic related to BTO displays a ferroelectric transition at TC ~ 293 K and a dielectric relaxation about 10 MHz . These ceramics could be of interest for electronic applications and especially for capacitors manufacturing with a low factory cost .

38. TYPE I CAPACITORS Pararaelectric dielectrics ’r (293K) : 6 à 300 tan  (293K) < 3.10-3 (stable with frequency ) ’r= f(T): relatively stable tan  = f(T) : relatively stable ’r (T) - ’r (293K) (- 3000 to +300 ppm / °C) ’r (293K) Aging: negligible

39. NORMS OF TYPE II CLASS Z5U CAPACITORS Ferroelectric dielectric 5000 ’r (293K)  9000 ’r (T) - ’r (293K) / ’r (293K) = +22 % at 283 K. ’r (T) - ’r (293K) / ’r (293K) = - 56 % at 358 K. tan  < 2.5 % .

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