DIELECTRIC PROPERTIES DIELECTRIC PROPERTIES OF ATiO3 CERAMICS OF ATiO3 CERAMICS ( A=Ca,Sr, Ba) SINTERED ( A=Ca,Sr, Ba) SINTERED WITH 5 Mol. % OF LiF AND WITH 5 Mol. % OF LiF AND CaF2CaF2

L . Taïbi - Benziada ; Y. SedkaouiAlgeria

AMOMEN ’2011, October 27 - 29 2011, Kenitra, MAROCCO

SUMMARYSUMMARY INTRODUCTIONINTRODUCTION EXPERIMENTAL EXPERIMENTAL PROCEDURESPROCEDURES

RESULTS AND RESULTS AND DISCUSSIONDISCUSSION

CONCLUSIONCONCLUSION

INTRODUCTINTRODUCTIONION

INTEREST FOR INTEREST FOR MATERIALS MATERIALS

MaterialsMaterials have always represented an have always represented an essential aspect of essential aspect of Human Society Human Society ..

Nowadays, the Nowadays, the MaterialMaterial became synonymous became synonymous with with Existence Existence for anyfor any Industry Industry ..

In new In new Technologies of informations and Technologies of informations and commu-nicationscommu-nications, the , the ProgressProgress and and SuccessSuccess are closely linked to the development of are closely linked to the development of Advanced CeramicsAdvanced Ceramics with with higher higher and and higherhigher performances but also with performances but also with lower lower and and lowerlower factory cost to be competi-tive on the huge factory cost to be competi-tive on the huge market of microelectronics .market of microelectronics .

APPLICATIONS OF APPLICATIONS OF CERAMICSCERAMICS

Conventional Ceramics

Engineering Ceramics

Microstructure

ABOABO33 RELATED RELATED MATERIALSMATERIALS

Among these new technical ceramics, Among these new technical ceramics, ABOABO33 perovskitesperovskites and their solid solid solutions are and their solid solid solutions are of great interest for the of great interest for the Microelectronic Microelectronic Industry Industry ..

With the devices miniaturization, With the devices miniaturization, ATiOATiO33 ceramics became the ceramics became the key materials key materials for the for the devevopment of devevopment of smartsmart systems systems with high with high level of intelligence .level of intelligence .

Up to now, the varied Up to now, the varied PZTPZT have dominated have dominated the market of microelectronic the market of microelectronic componentscomponents. . However, theHowever, the toxicitytoxicity of of Pb Pb is a serious is a serious threatthreat to human to human health health and and environment environment ..

APPLICATIONS OF ABOAPPLICATIONS OF ABO33 PEROVSKITESPEROVSKITES

CapacitorsCapacitorsSensorsSensorsResonatorsResonatorsPiezoelectric actuatorsPiezoelectric actuatorsPyroelectric infrared detectorsPyroelectric infrared detectorsElectro-optical modulatorsElectro-optical modulatorsComputer memories...Computer memories... FRAMSFRAMS

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

FRAMSFRAMS

DRAMSDRAMS

HDDHDD

OBJECTIVESOBJECTIVESThe sintering at low temperature of The sintering at low temperature of

lead freelead free ceramics related to ceramics related to ATiOATiO33 ( A = Ca, Sr, Ba ) ( A = Ca, Sr, Ba ) with the aid of with the aid of 5 mol. % of CaF5 mol. % of CaF22 andand LiFLiF : :

0.95 ATiO0.95 ATiO33 + 0.05 CaF + 0.05 CaF22 + 0.05 LiF + 0.05 LiF

The investigation of the The investigation of the dielectric dielectric propertiesproperties in the obtained samples . in the obtained samples .

PROPERTIES OF ATiO3 PROPERTIES OF ATiO3 CERAMICS CERAMICS

( A=Ca,Sr, Ba)( A=Ca,Sr, Ba)

Calcium Titanate Calcium Titanate CaTiOCaTiO33

Ferroelectric Ferroelectric perovskite : perovskite : TTCC ~ ~ 105 K105 K Phase TransitionsPhase Transitions

Orthorhombic Tetragonal Orthorhombic Tetragonal Cubic Cubic

Pbnm Pbnm I4/mcmI4/mcm Pm3mPm3m

Quantum Paraelectric Quantum Paraelectric Symmetry at room temperatureSymmetry at room temperature

Orthorhombic : Orthorhombic :

aa = 5.443 Å ; = 5.443 Å ; b b = 7.653 Å ; = 7.653 Å ; cc = 5.376 Å= 5.376 Å

1498 K 1634 K

Strontium Titanate Strontium Titanate SrTiOSrTiO33

Phase Transitions Phase Transitions

Orthorhombic Tetragonal Orthorhombic Tetragonal Cubic Cubic

Resonance FrequenciesResonance Frequencies

ffr1r1 = 3 x 10= 3 x 101212 Hz Hz ffr2r2 = 1.65 x 10 = 1.65 x 1013 13 Hz Hz

Quantum Paraelectric or incipient Quantum Paraelectric or incipient ferroelectricferroelectric

Symmetry at 300 K Symmetry at 300 K

Cubic ( Cubic ( Pm3mPm3m ) ) a a = 3.905 Å= 3.905 Å

65 K 110 K

Barium Titanate Barium Titanate BaTiOBaTiO33

Ferroelectric Ferroelectric perovskite : perovskite : TTC C ~~ 393 K393 K

Phase Transitions Phase Transitions

Rhombohedral Orthorhombic Rhombohedral Orthorhombic R3m R3m

Amm2Amm2 Tetragonal CubicTetragonal Cubic P4mm Pm3mP4mm Pm3m Relaxation Frequency : Relaxation Frequency : ffrr ~ ~ 500 MHz 500 MHz

Symmetry at room temperature Symmetry at room temperature

Tetragonal : Tetragonal : aa = 3.992 Å = 3.992 Å bb = 4.036 Å= 4.036 Å

183 K 268 K

393 K

EXPERIMENTAL EXPERIMENTAL PROCEDURESPROCEDURES

SAMPLES SAMPLES PREPARATIONS (1)PREPARATIONS (1)

ACOACO33 , , TiOTiO2 2 , , CaFCaF22 and and LiF LiF were pre-were pre-heated at heated at 150 °C 150 °C to eliminate to eliminate moisturemoisture and to avoid any and to avoid any hydrolysis hydrolysis during the during the sintering process.sintering process.

Stoichiometric titanates Stoichiometric titanates ATiOATiO33 were were then synthesized by calcination in then synthesized by calcination in air air ::

ACOACO33 + TiO + TiO22 ATiO ATiO33 + + COCO22

SAMPLES SAMPLES PREPARATIONS (2)PREPARATIONS (2)

Various Various chemical chemical compositions compositions were were prepared and ground in ethanol : prepared and ground in ethanol :

0.95 ATiO0.95 ATiO3 3 + 0.05 CaF+ 0.05 CaF2 2 + 0.05 LiF+ 0.05 LiF

The mixtures thus obtained were The mixtures thus obtained were cold-pressed to cold-pressed to pelletspellets with a with a binderbinder under a pressure of under a pressure of 100 MPa 100 MPa and and sintered in sintered in air air at at 1000 °C1000 °C for for 2 h 2 h on on zircona plates.zircona plates.

ACO3+TiO2

Grinding, Calcination

ATiO3+CO25 % ( CaF2+LiF )

Grinding

Sintering 1000 °C , 2 h

A0.95 Ca0.05 ( Ti0.95Li0.05 )O2.85 F0.15

METHODS OF METHODS OF INVESTIGATIONS INVESTIGATIONS

The purity and the symmetry were The purity and the symmetry were checked by checked by X-Ray diffractionX-Ray diffraction on crushed on crushed ceramics at ceramics at 300 K 300 K . .

The ceramic’s microstructures were The ceramic’s microstructures were observed by observed by Scanning Electron Scanning Electron MicroscopyMicroscopy on fractured samples . on fractured samples .

Dielectric measurementsDielectric measurements were carried out were carried out as a function of temperature ( as a function of temperature ( 100 K - 100 K - 550 K 550 K ) and frequency ( ) and frequency ( 101022 Hz Hz - - 4x104x1066 HzHz ) )..

RESULTS AND RESULTS AND DISCUSSIONDISCUSSION

X-RAY X-RAY DIFFRACTIONDIFFRACTION

The X-Ray peaks of The X-Ray peaks of CTO oxyfluorideCTO oxyfluoride are are indexed in an indexed in an orthorhombic orthorhombic cell .cell .

The XRD peaks of The XRD peaks of fluorinated STO fluorinated STO are are indexed in an indexed in an orthorhombicorthorhombic multiple cell. multiple cell. The parametersThe parameters of the of the orthorhombic orthorhombic cellcell are are related to that of related to that of STOSTO : :

aaoo ~ ~ (2)(2)1/21/2 a acc ; b ; boo ~ ~ 4 4 aacc ; c ; coo ~ ~ (2)(2)1/21/2 a acc

The XRD peaks of The XRD peaks of BTO oxyfluorideBTO oxyfluoride are are indexed in a indexed in a cubic cubic cell.cell.

Sample a (Å) b (Å) c (Å)

CTO 5.443 7.653 5.376

CTO oxyfluoride 5.446 7.644 5.385

STO 3.905 - -

STO oxyfluoride 6.371 15.638 6.515

BTO 3.992 4.036 -

BTO oxyfluoride 4.004 - -

Unit Cell Unit Cell ParametersParameters

SEM SEM OBSERVATIONSOBSERVATIONS

The micrograhs of The micrograhs of A(Ti,Li)(O,F)A(Ti,Li)(O,F)33

ceramics are ceramics are monophasicmonophasic . . ATiOATiO33 ceramics are very ceramics are very brittle brittle ( ΔΦ/Φ ( ΔΦ/Φ

<< 3 % 3 % )) and and porous porous whereas the whereas the fluoridated ceramicsfluoridated ceramics are are compactcompact and and very very hard hard ( ( 13 %13 % ΔΦ/Φ ΔΦ/Φ 22 %22 % ) . ) .

The fluoride mixture The fluoride mixture CaFCaF22 + LiF + LiF plays plays a double role: - as a double role: - as substituant substituant and - and - as as sintering agentsintering agent . .

Micrographs of Micrographs of CaTiOCaTiO33 and and CaTiCaTi0.950.95LiLi0.050.05OO2.852.85FF0.150.15

CaTiO3

= 2.1 %

CaTi0.95Li0.05O2.85F0.75

= 21.9 %

Micrographs of Micrographs of SrTiOSrTiO33 and and SrSr0.950.95CaCa0.050.05TiTi0.950.95LiLi0.050.05OO2.852.85FF0.15 0.15

Sr0.95Ca0.05Ti0.95Li0.05O2.85F0.85

= 18.7 %

SrTiO3

= 1.1 %

Micrograph of Micrograph of BaBa0.950.95CaCa0.050.05TiTi0.950.95LiLi0.050.05OO2.852.85FF0.15 0.15

Ba0.95Ca0.05Ti0.95Li0.05O2.85F0.85

= 13.5 %

DIELECTRIC DIELECTRIC PROPERTIES OF PROPERTIES OF

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

CERAMICSCERAMICS

100 200 300 400 500 6000

100

200

300

400

500

600

700

800

900 10

2Hz

5.102Hz

10.102Hz

50.102Hz

100.102Hz

500.102Hz

1000.102Hz

2000.102Hz

' r

T(°C)

ε'r

T (K)

102 Hz

5x102 Hz

103 Hz

5x103 Hz

104 Hz5x104 Hz

105 Hz

2x105 Hz

Temperature dependence Temperature dependence of ε’of ε’r r for for CaTiCaTi0.950.95LiLi0.050.05OO2.852.85FF0.15 0.15

ceramicceramic

A A phase phase transitiontransition is detected is detected around around 283 K283 K . .The The quantum quantum paraelectriparaelectricc behaviour behaviour of of CaTiOCaTiO33 disappears disappears ..

100 200 300 400 500 600

0

200

400

600

800

1000 10

2Hz

5.102Hz

10.102Hz

50.102Hz

100.102Hz

500.102Hz

1000.102Hz

2000.102Hz

T(°C)

'' r

ε"r

T (K)

102 Hz

5x102 Hz

103 Hz

5x103 Hz

104 Hz5x104 Hz

105 Hz

2x105 Hz

Temperature dependence Temperature dependence of ε’’of ε’’r r for for CaTiCaTi0.950.95LiLi0.050.05OO2.852.85FF0.15 0.15

ceramicceramic

ε"ε"rr exhibits exhibits a a frequency frequency dependent dependent peak peak around around 283 283 KK . .

Below Below 250 250 K K , the , the frequency frequency dispersion dispersion is is negligiblenegligible

Frequency dependence of ε’Frequency dependence of ε’r r

and ε’’and ε’’r r for for CaTiCaTi0.950.95LiLi0.050.05OO2.852.85FF0.15 0.15 ceramic ceramic

5,0 5,5 6,0 6,5 7,0 7,5 8,00

10

20

30

40

50

60

70

80

90

100

logf(Hz)

0

1

2

3

4

5

6

7

8

9

10

''

r

'

r

The real The real permittivity permittivity ε’ ε’ r r is nearly is nearly constant constant (~(~80 80 ) .) . In the In the opposite, the opposite, the imaginary imaginary component component ε"ε"rr exhibits a exhibits a broadbroad minimum minimum at 4.5 MHz 4.5 MHz .

102 Hz

5x102 Hz

103 Hz

5x103 Hz

104 Hz5x104 Hz

105 Hz

2x105 Hz

Temperature dependence of ε’Temperature dependence of ε’r r

for Srfor Sr0.950.95CaCa0.050.05TiTi0.950.95LiLi0.050.05OO2.852.85FF0.150.15 ceramicceramic

ContrariwisContrariwise to e to CTOCTO , , the the quantum quantum paraelectricparaelectric behaviour behaviour of of STOSTO still still persistspersists . . No No phasephase transitiontransition is is detected . detected .

Temperature dependence of ε’’Temperature dependence of ε’’r r

for Srfor Sr0.950.95CaCa0.050.05TiTi0.950.95LiLi0.050.05OO2.852.85FF0.150.15 ceramicceramic

102 Hz5x102 Hz

103 Hz5x103 Hz104 Hz5x104 Hz105 Hz2x105 Hz

TheThe increase increase in in εε''rr and and εε" " r r beyond beyond 400 400 KK is ascribed is ascribed to the to the electrical conductivityconductivity of lithium ion of lithium ion LiLi++ . .

Frequency dependence of ε’Frequency dependence of ε’r r and ε’’and ε’’r r

for Srfor Sr0.950.95CaCa0.050.05TiTi0.950.95LiLi0.050.05OO2.852.85FF0.150.15 ceramic at 300 Kceramic at 300 K

5,0 5,5 6,0 6,5 7,0 7,5 8,00

20

40

60

80

100

120

140

160

180

200

0

2

4

6

8

10

12

14

16

18

logf(Hz)

'

r ''

r

The real The real permittivity permittivity ε’ ε’ r r is is practically practically constant constant (~(~180 180 ).).

In the In the opposite, the opposite, the imaginary imaginary component component ε"ε"rr exhibits a exhibits a broadbroad minimum minimum at 5 .6 MHz 5 .6 MHz .

Temperature dependence of ε’Temperature dependence of ε’r r

for Bafor Ba0.950.95CaCa0.050.05TiTi0.950.95LiLi0.050.05OO2.852.85FF0.150.15 ceramicceramic

150 200 250 300 350 400 450500

1000

1500

2000

2500

3000

3500

Die

lec

tric

pe

rmit

tiv

ity

Temperature (K)

A A diffuse diffuse phase phase transition transition is is depicted at depicted at the the ferroelectric ferroelectric Curie Curie temperature T c ~ 293 KT c ~ 293 K ..

Temperature dependence of Temperature dependence of tantanδδ for for BaBa0.950.95CaCa0.050.05TiTi0.950.95LiLi0.050.05OO2.852.85FF0.150.15 ceramicceramic

150 200 250 300 350 400 450

5

10

15

20

25

30

35

Die

lec

tric

los

se

s x

103

Temperature (K)

The The permittivitypermittivity broad peakbroad peak is associated associated to to a a minimumminimum of of the the losses losses ..

Frequency dependence of ε’Frequency dependence of ε’r r and ε’’and ε’’r r

for Bafor Ba0.950.95CaCa0.050.05TiTi0.950.95LiLi0.050.05OO2.852.85FF0.150.15 ceramic at 300 Kceramic at 300 K

4000

2

5 6 7 8

log f (Hz)

ε'r

ε"r

3000

2000

1000

The The complex complex permittivity permittivity exhibits a exhibits a dielectric dielectric relaxation relaxation around around 10 10 MHzMHz ..

CONCLUSIOCONCLUSIONN

ATiO3ATiO3 ceramics ( A = Ca, Sr, Ba ) were sintered ceramics ( A = Ca, Sr, Ba ) were sintered at at low temperaturelow temperature with the aid of with the aid of 5 mol.% of 5 mol.% of LiF+CaFLiF+CaF22

The The oxyfluorideoxyfluoride deriving from deriving from CTO CTO exhibits a exhibits a peak of peak of ε‘ ε‘ r r and and ε"ε"rr around around 283 K 283 K . .

For For STOSTO, , no phase transitionno phase transition is detected in the is detected in the temperature range investigated. temperature range investigated.

The The ceramicceramic related to related to BTO BTO displays a displays a ferroelectric transition ferroelectric transition at at TTC C ~ 293 K ~ 293 K and a and a dielectric dielectric relaxationrelaxation about about 10 MHz 10 MHz . .

These ceramics could be of interest for These ceramics could be of interest for electronic applicationselectronic applications and especially and especially for for capacitorscapacitors manufacturing manufacturing with a with a low factory low factory cost cost ..

TYPE I CAPACITORSTYPE I CAPACITORS

Pararaelectric Pararaelectric dielectricsdielectrics ’’rr (293K) : (293K) : 6 à 3006 à 300 tan tan (293K) < (293K) < 3.103.10-3 -3 ((stable stable withwith

frequency frequency )) ’’rr= f(T): = f(T): relatively stable relatively stable tan tan = f(T) : = f(T) : relatively stable relatively stable

    ’’rr (T) - (T) - ’’rr (293K) ( (293K) (- 3000 - 3000 toto +300 ppm / °C +300 ppm / °C))

’’rr (293K) (293K) Aging: Aging: negligiblenegligible

NORMS OF TYPE II CLASS NORMS OF TYPE II CLASS Z5U CAPACITORSZ5U CAPACITORS

Ferroelectric Ferroelectric dielectricdielectric50005000 ’’rr (293K) (293K) 90009000

’’rr (T) - (T) - ’’rr (293K) / (293K) / ’’rr (293K) = (293K) = +22 %+22 % at at 283 K283 K . .

’’rr (T) - (T) - ’’rr (293K) / (293K) / ’’rr (293K) = (293K) = - - 56 %56 % at at 358 K358 K ..

tan tan < < 2.5 %2.5 % . .

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