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 , Kenitra, MAROCCO

SUMMARY  INTRODUCTION  EXPERIMENTAL PROCEDURES  RESULTS AND DISCUSSION  CONCLUSION

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 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.

APPLICATIONS OF CERAMICS Conventional Ceramics Engineering Ceramics Microstructure

ABO 3 RELATED MATERIALS  Among these new technical ceramics, ABO 3 perovskites and their solid solid solutions are of great interest for the Microelectronic Industry.  With the devices miniaturization, ATiO 3 ceramics became the key materials for the devevopment of smart systems with high level of 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 ABO 3 PEROVSKITES  Capacitors  Sensors  Resonators  Piezoelectric actuators  Pyroelectric infrared detectors  Electro-optical modulators  Computer memories... FRAMS

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

OBJECTIVES  The sintering at low temperature of lead free ceramics related to ATiO 3 ( A = Ca, Sr, Ba ) with the aid of 5 mol. % of CaF 2 and LiF : 0.95 ATiO CaF LiF  The investigation of the dielectric properties in the obtained samples.

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

Calcium Titanate CaTiO 3  Ferroelectric perovskite : T C ~ 105 K  Phase Transitions Orthorhombic Tetragonal Cubic Orthorhombic Tetragonal Cubic Pbnm I4/mcm Pm3m Pbnm I4/mcm Pm3m  Quantum Paraelectric  Symmetry at room temperature Orthorhombic : Orthorhombic : a = Å ; b = Å ; c = Å 1498 K1634 K

Strontium Titanate SrTiO 3  Phase Transitions Orthorhombic Tetragonal Cubic Orthorhombic Tetragonal Cubic  Resonance Frequencies f r1 = 3 x Hz f r2 = 1.65 x Hz f r1 = 3 x Hz f r2 = 1.65 x Hz  Quantum Paraelectric or incipient ferroelectric  Symmetry at 300 K Cubic ( Pm3m ) a = Å Cubic ( Pm3m ) a = Å 65 K110 K

Barium Titanate BaTiO 3  Ferroelectric perovskite : T C ~ 393 K  Phase Transitions Rhombohedral Orthorhombic Rhombohedral Orthorhombic R3m Amm2 R3m Amm2 Tetragonal Cubic Tetragonal Cubic P4mm Pm3m P4mm Pm3m  Relaxation Frequency : f r ~ 500 MHz  Symmetry at room temperature Tetragonal : a = Å b = Å 183 K268 K 393 K

EXPERIMENTAL PROCEDURES

SAMPLES PREPARATIONS (1)  ACO 3, TiO 2, CaF 2 and LiF were pre- heated at 150 °C to eliminate moisture and to avoid any hydrolysis during the sintering process.  Stoichiometric titanates ATiO 3 were then synthesized by calcination in air : ACO 3 + TiO 2 ATiO 3 + CO 2 ACO 3 + TiO 2 ATiO 3 + CO 2

SAMPLES PREPARATIONS (2)  Various chemical compositions were prepared and ground in ethanol : 0.95 ATiO CaF 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.

ACO 3 +TiO 2 Grinding, Calcination ATiO 3 +CO 2 5 % ( CaF 2 +LiF ) Grinding Sintering 1000 °C, 2 h A 0.95 Ca 0.05 ( Ti 0.95 Li 0.05 )O 2.85 F 0.15

METHODS OF INVESTIGATIONS  The purity and the symmetry were checked by X- Ray diffraction on crushed ceramics at 300 K.  The ceramic’s microstructures were observed by Scanning Electron Microscopy on fractured samples.  Dielectric measurements were carried out as a function of temperature ( 100 K K ) and frequency ( 10 2 Hz - 4x10 6 Hz ).

RESULTS AND DISCUSSION

X-RAY DIFFRACTION  The X-Ray peaks of CTO oxyfluoride are indexed in an orthorhombic cell.  The XRD peaks of fluorinated STO are indexed in an orthorhombic multiple cell. The parameters of the orthorhombic cell are related to that of STO : a o ~ (2) 1/2 a c ; b o ~ 4 a c ; c o ~ (2) 1/2 a c a o ~ (2) 1/2 a c ; b o ~ 4 a c ; c o ~ (2) 1/2 a c  The XRD peaks of BTO oxyfluoride are indexed in a cubic cell.

Unit Cell Parameters

SEM OBSERVATIONS  The micrograhs of A(Ti,Li)(O,F) 3 ceramics are monophasic.  ATiO 3 ceramics are very brittle ( ΔΦ/Φ < 3 % ) and porous whereas the fluoridated ceramics are compact and very hard ( 13 %  ΔΦ/Φ  22 % ).  The fluoride mixture CaF 2 + LiF plays a double role: - as substituant and - as sintering agent.

Micrographs of CaTiO 3 and CaTi 0.95 Li 0.05 O 2.85 F 0.15 CaTiO 3  = 2.1 % CaTi 0.95 Li 0.05 O 2.85 F 0.75  = 21.9 %

Micrographs of SrTiO 3 and Sr 0.95 Ca 0.05 Ti 0.95 Li 0.05 O 2.85 F 0.15 Sr 0.95 Ca 0.05 Ti 0.95 Li 0.05 O 2.85 F 0.85  = 18.7 % SrTiO 3  = 1.1 %

Micrograph of Ba 0.95 Ca 0.05 Ti 0.95 Li 0.05 O 2.85 F 0.15 Ba 0.95 Ca 0.05 Ti 0.95 Li 0.05 O 2.85 F 0.85  = 13.5 %

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

ε' r T (K) 10 2 Hz 5x10 2 Hz 10 3 Hz 5x10 3 Hz 10 4 Hz 5x10 4 Hz 10 5 Hz 2x10 5 Hz Temperature dependence of ε’ r for CaTi 0.95 Li 0.05 O 2.85 F 0.15 ceramic  A phase transition is detected around 283 K.  The quantum paraelectric behaviour of CaTiO 3 disappears.

ε" r T (K) 10 2 Hz 5x10 2 Hz 10 3 Hz 5x10 3 Hz 10 4 Hz 5x10 4 Hz 10 5 Hz 2x10 5 Hz Temperature dependence of ε’’ r for CaTi 0.95 Li 0.05 O 2.85 F 0.15 ceramic  ε" r exhibits a frequency dependent peak around 283 K.  Below 250 K, the frequency dispersion is negligible

Frequency dependence of ε’ r and ε’’ r for CaTi 0.95 Li 0.05 O 2.85 F 0.15 ceramic  The real permittivity ε’ r is nearly constant (~80 ).  In the opposite, the imaginary component ε" r exhibits a broad minimum 4.5 MHz  In the opposite, the imaginary component ε" r exhibits a broad minimum at 4.5 MHz.

10 2 Hz 5x10 2 Hz 10 3 Hz 5x10 3 Hz 10 4 Hz 5x10 4 Hz 10 5 Hz 2x10 5 Hz Temperature dependence of ε’ r for Sr 0.95 Ca 0.05 Ti 0.95 Li 0.05 O 2.85 F 0.15 ceramic  Contrariwise to CTO, the quantum paraelectric behaviour of STO still persists.  No phase transition is detected.

Temperature dependence of ε’’ r for Sr 0.95 Ca 0.05 Ti 0.95 Li 0.05 O 2.85 F 0.15 ceramic 10 2 Hz 5x10 2 Hz 10 3 Hz 5x10 3 Hz 10 4 Hz 5x10 4 Hz 10 5 Hz 2x10 5 Hz The increase in ε' r and ε" r beyond 400 K is ascribed to the conductivity of lithium ion Li +. The increase in ε' r and ε" r beyond 400 K is ascribed to the electrical conductivity of lithium ion Li +.

Frequency dependence of ε’ r and ε’’ r for Sr 0.95 Ca 0.05 Ti 0.95 Li 0.05 O 2.85 F 0.15 ceramic at 300 K  The real permittivity ε’ r is practically constant (~180 ).  In the opposite, the imaginary component ε" r exhibits a broad minimum 5.6 MHz  In the opposite, the imaginary component ε" r exhibits a broad minimum at 5.6 MHz.

Temperature dependence of ε’ r for Ba 0.95 Ca 0.05 Ti 0.95 Li 0.05 O 2.85 F 0.15 ceramic A diffuse phase transition is depicted at the ferroelectric Curie T c ~ 293 K. A diffuse phase transition is depicted at the ferroelectric Curie temperature T c ~ 293 K.

Temperature dependence of tanδ for Ba 0.95 Ca 0.05 Ti 0.95 Li 0.05 O 2.85 F 0.15 ceramic The permittivity broad peak associated to a minimum of the losses. The permittivity broad peak is associated to a minimum of the losses.

Frequency dependence of ε’ r and ε’’ r for Ba 0.95 Ca 0.05 Ti 0.95 Li 0.05 O 2.85 F 0.15 ceramic at 300 K log f (Hz) ε' r ε" r The complex permittivity exhibits a dielectric relaxation around 10 MHz.

CONCLUSION

 ATiO3 ceramics ( A = Ca, Sr, Ba ) were sintered at low temperature with the aid of 5 mol.% of LiF+CaF 2  The oxyfluoride deriving from CTO exhibits a peak of ε‘ r and ε" r around 283 K.  For STO, no phase transition is detected in the temperature range investigated.  The ceramic related to BTO displays a ferroelectric transition at T C ~ 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.

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

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 %.

THANK YOU FOR YOUR ATTENTION