Laldja TAÏBI – BENZIADA(http://perso.usthb.dz/~lbenziada)

Faculty of Chemistry, USTHB, Algiers, ALGERIA

EFFECT OF LITHIUM FLUORIDE ON THE DIELECTRIC

PROPERTIES OF BARIUM TITANATE

IUPAC 9th International Conference on Novel Materials and Synthesis (NMS – IX)October 17 – 22 , 2013, Shanghai, CHINA

SUMMARY• Introduction• Experimental procedures• Results and discussion• Conclusion• References

INTRODUCTION

INTEREST FOR MATERIALS• Materials have always represented an essential aspect of

human society.

• Nowadays, the material became synonymous with existence for any industry.

• In new technologies of informations and communications, 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.

CERAMICS PRODUCTSConventional ceramics

MicrostructureEngineering ceramics

ABO3 RELATED MATERIALS• Among these new technical ceramics, ABO3 perovskites and

their solid solutions are very attractive for microelectronic industry.

• With the devices miniaturization, ATiO3 ceramics became the key materials for the development of smart systems with artificial intelligence.

• Up to now, the varied PZT have dominated the market of microelectronic components. However, the toxicity of Pb is a serious threat to human health and environment.

APPLICATIONS OF ABO3 PEROVSKITES

• Capacitors

• Sensors

• Resonators

• Piezoelectric actuators

• Pyroelectric infrared detectors

• Electro-optical modulators

• Computer and mobile phone memories… FRAMs

COMPUTER’S MEMORIES

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

OBJECTIVES• To lower both the sintering temperature

(Tsint. ~ 1400 ° C) and the ferroelectric Curie temperature (TC = 120 ° C) of BaTiO3

ceramics using LiF as additive.

• To reinvestigate the effect of lithium fluoride on dielectric properties of BaTiO3 ceramics sintered in various conditions.

• Phase transitions :

Rhombohedral Orthorhombic Tetragonal Cubic

• Ferroelectric Curie temperature : TC = 393 K

• Relaxation frequency : fr = 500 MHz

• Symmetry at room temperature: Tetragonal

193 K 278 K 393 K

BaTiO3 PROPERTIES

BaTiO3 UNIT CELL AT 300 K

O

Ti

Ba

a = 3.998 Å

c = 4.018 Å

EXPERIMENTAL PROCEDURES

SAMPLES PREPARATIONS• Barium titanate with various ratio BaO/TiO2 was previously

synthesized by calcination of BaCO3 and TiO2 at 1100 ° C:

0.97 BaCO3 + TiO2 0.97 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)

• Several chemical compositions were then prepared from the varied BTO and LiF then wet-ground in ethanol :

(1-x) wt. % BTO + x wt. % LiF

• The powder mixtures were cold-pressed to pellets with an organic binder. The disks thus obtained were sintered in various conditions.

x BaCO3 + y TiO2

Grinding, Calcination 1100 °C

BaTiO3+CO2x wt. % LiF

(1-x) % BaTiO3 + x % LiF

Grinding

Sintering (T °C)

Ba(Ti, Li)(O, F)3

METHODS OF INVESTIGATIONS• X-ray diffraction analyzes were carried out at room temperature on

crushed ceramics in the 2 range 10 – 90 °.

• Scanning Electron Microscopy observations were performed on fractured ceramics.

• Dielectric measurements were carried out under vacuum at 1 kHz between 180 K and 500 K.

• Ceramics were investigated by Auger microprobe and thermal analyses.

• Chemical analyses were performed and fluorine and lithium losses were calculated.

RESULTS AND DISCUSSION

DRX spectra of BaTiO3 ceramics sintered with 2 wt. % LiF at 950 ° C for 2 h

BTO (1.03)

BTO (1.00)

BTO (0.97)

2 (°)

BaO/TiO2 a (Å) c(Å)0.97 3.996 4.0321.00 4.011 -1.03 4.014 -

• The unit cell remains tetrago-nal for BTO (0.97).

• The lattice symmetry becomes cubic for BTO (1.00) and BTO (1.03).

Effect of BaO/TiO2 ratio on the permittivity of BaTiO3

ceramics sintered with 2 wt. % LiF at 950 ° C for 2 h

BaO/TiO2 TC(K) ’r tan

0.97 0.05 303 1200 0.015

1.00 0.145 298 4200 0.008

1.03 0.17 283 5700 0.006

• Excess of TiO2 inhibits the sintering and ’r.

• Excess of BaO enhances the sintering and ’r.

• The best dielectric characteristics are obtained with BTO (1.03)

Effect of LiF amount on permittivity of BaTiO3 (1.00) ceramics sintered at 950 ° C for 2 h

LiF TC(K) ’r tan

1 wt. % 0.14 338 3650 0.013

2 wt. % 0.145 298 4200 0.008

3 wt. % 0.145 303 5200 0.007

• is practically constant.

• TC decreases and ’r increases.

• The best dielectric characteristics are observed with 3 wt. % of LiF.

LiF TC(K) ’r tan1 wt. % 0.06 313 1500 0.010

2 wt. % 0.17 283 5700 0.006

3 wt. % 0.16 268 6100 0.006

Effect of LiF amount on permittivity of BaTiO3 (1.03) ceramics sintered at 950 ° C for 2 h

• is very low for 1 wt. % of LiF .

• TC decreases and ’r increases.

• The best dielectric characteristics are obtained with 3 wt. % of LiF.

tsint. (h) TC(K) ’r tan2 0.145 298 4200 0.0088 0.155 353 3100 0.005

Effect of holding time on permittivity of BaTiO3 (1.00) ceramics sintered with 2 wt. % LiF at 950 ° C

• increases slightly.

• TC increases and ’r decreases.

• The best dielectric characteris-tics are obtained for tsint. = 2 h.

tsint. (h) TC(K) ’r tan

2 0.17 283 5700 0.006

8 0.18 293 3900 0.004

Effect of holding time on permittivity of BaTiO3 (1.03) ceramics sintered with 2 wt. % LiF at 950 ° C

• increases slightly.

• TC increases and ’r decreases.

• The best dielectric characteris-tics are obtained for tsint. = 2 h.

Tsint.(°C) TC(K) ’r tan750 0.02 373 300 0.015

850 0.14 283 3400 0.008

950 0.145 298 4200 0.008

1100 0.15 288 5700 0.005

Effect of sintering temperature on permittivity of BaTiO3 (1.00) ceramics sintered with 2 wt. % LiF for 2 h

• increases.

• TC decreases and ’r increases.

• The best dielectric characteristics are obtained for Tsint. = 1100 ° C.

Tsint. (°C) TC(K) ’r tan750 0.095 393 950 0.012

850 0.165 281 2750 0.008

950 0.17 283 5700 0.006

1100 0.17 263 5250 0.005

Effect of sintering temperature on permittivity of BaTiO3 (1.03) ceramics sintered with 2 wt. % LiF for 2 h

• increases.

• TC decreases and ’r increases then decreases.

• The best dielectric characteristics are obtained for Tsint. = 950° C.

Temperature dependence of permittivity and losses for BaTiO 3 (1.03) ceramic sintered with 2 wt. % LiF at 950 ° C for 2 h in free air

Atmosphere TC(K) ’r tan

Free air 0.17 283 5700 0.006

Sealed tube 0.06 383 800 0.017

Effect of sintering atmosphere on permittivity of BaTiO3 (1.03) ceramics sintered at 950 °C with 2 wt. % LiF for 2 h

• The best shrinkage and the best dielectric characteris-tics are obtained when sintering is performed in free air.

Sintering TC(K) ’r tan

950°C, 2h, air 0.17 283 5700 0.006

950°C, 2h, air+950°C, 48h, ST

0.17 263 6750 0.006

950°C, 2h, air+1200°C, 2h, ST

0.17 248 8650 0.006

Temperature dependence of permittivity of BaTiO3 (1.03) ceramics sintered with 2 wt. % LiF in various conditions

• The best dielectric characteris-tics are obtained when sintering is performed at 950 °C for 2 h in free air then at 1200 °C in sealed tube for 2 h.

Tsint. (° C) TiO2 (wt. %) BaO (wt.%) F (wt.%) Li (wt.%) F losses (wt.%) Li losses (wt.%)

850 34.0 65.08 1.15 0.29 21 45900 34.35 65.08 1.11 0.25 24 53950 34.50 65.09 0.77 0.18 47 661100 34.80 65.08 0.47 0.094 68 82

Chemical composition, fluorine and lithium losses of BTO (1.03) ceramics sintered with 2 wt. % LiF for 2 h at various temperatures

• Li and F losses increase with increasing the sintering temperature. Li losses are more important than those of F.

• The exothermic peak at 280 °C is probably due to the hydrolysis of LiF :

LiF + H2O LiOH + HF

• The endothermic peak at around 630 °C is ascribed to Li and F losses.

• The weight loss reaches 50 % after heating at 950 °C for 2 h.

DTA and TG thermograms of 98 wt. % BTO (1.03) + 2 wt. % LiF

DTA

TG

280 °C

630 °C

98 wt. % BTO (1.03) + 2 wt. % LiF 98 wt. % BTO (1.03) + 2 wt. % LiF

Micrographs of ceramics sintered at 850 or 950 °C

• The grain size increases and the porosity decreases with increasing the sintering temperature.

850°C 950°C

Auger spectra of BaTiO3 (1.03) fractured ceramics sintered with 2 wt. % LiF at 950 ° C for 2 h

Before sputtering After sputtering

• Ba, Li, O, Ti and F elements are detected and a composition gradient is observed in the grains.

CONCLUSION

• The effect of LiF on dielectric properties of BaTiO3 with different ratio BaO/TiO2 and sintered in various conditions has been reinvestigated.

• As result, an excess of TiO2 inhibits the sintering process and the permittivity. On the other hand, BaO excess enhances both the densification and the dielectric characteristics. The best densification is obtained with BTO (1.03).

• The addition of LiF to BTO (1.00) or BTO (1.03) lowers simultaneously 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) sintered with 2 wt. % of LiF at 950 ° C for 2 h could be used for Z5U multilayer capacitors manufacturing.

• Ferroelectric dielectric

• 5000 ’r (293K) 9000

• ’r (T) - ’r (293K) / ’r

(293K) = + 22 % at 283 K

• ’r (T) - ’r (293K) / ’r

(293K) = - 56 % at 356 K

• Tan (293K) 2.5 %

NORMS OF TYPE II CLASS Z5U CAPACITORS

+ 22 %

- 56 %

Z5U

98 wt. % BTO (1.03) + 2 wt. % LiF, 950 °C, 2 h

REFERENCES

• [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.

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