Additive Effects on Piezoelectric Properties of Leadfree Na0'5K0'5NbO3LiNbO3 Ceramics

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Additive Effects on Piezoelectric Properties of
Lead-free (Na0.5K0.5)NbO3LiNbO3 Ceramics
11th International Meeting on Ferroelectricity
September 5-9 , 2005Cataratas del Iguazú / Foz
do IguaçuArgentina / Brazil

• Chang Won Ahn, Sun Hee Kang, Hai Joon Lee and
  Ill Won Kim
• Department of Physics, University of Ulsan,
  680-749, Korea
• Mun Seok Choi, Jae Shin Lee
• School of Materials Science and Eng., University
  of Ulsan, 680-749, Korea
• Hyung Wook Kim, Byung Moon Jin
• Department of Physics, Dong-Eui University,
  Busan, 614-714, Korea
• cwahn_at_mail.ulsan.ac.kr
• kimiw_at_mail.ulsan.ac.kr

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Why Lead-Free Materials?

• Lead zirconium titanate (PZT) ceramics are
  high-performance piezoelectric materials, which
  are widely used in sensors, actuators and other
  electronic devices they contain more than 60
  weight percent of lead.
• Lead has recently been prohibited from many
  commercial applications and materials (for
  example, from solder, glass and pottery glaze)
  owing to concern regarding its toxicity.
• The European Commission has been agreed to a ban
  on four heavy metals (lead, cadmium, mercury, and
  hexavalent chromium) from 1st July 2006.

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Candidate Materials as Lead-free Piezoelectric
Ceramics
(Na,K)NbO3 ceramics
Merits - High Curie temperature (TC)
- Relatively high planar coupling coefficient
(kp) - Large piezoelectric
longitudinal response (d33)
Demerits - Poor sinterability by ordinary
sintering process. ? Lower
electrical properties
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Research of (Na0.5K0.5)NbO3-based Ceramics
Improve sinterability by additive

• (K,Na)NbO3 CuO, ZnO

• (K,Na)NbO3-BaTiO3

Y. Guo et al., JJAP 43, 6662 (2004).

• (K,Na)NbO3-SrTiO3

Y. Shimojo et al., J. Korean Phys. Soc. 46, 48
(2005).
Formation of a morphotropic phase boundary (MPB)
between tetragonal and orthorhombic phases

• (K,Na,Li)(Nb,Ta,Sb)O3

Y. Saito et al., Nature 432, 84 (2004).

• (K,Na,Li)NbO3

Y. Guo et al., APL 85, 4121 (2004).
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Experimental Process
Solid-State Reaction Method
(1-x)(Na0.5K0.5)NbO3-xLiNbO3 (1-x)NKN-xLN x
0, 0.02, 0.04, 0.05, 0.6, 0.08, 0.10
K2CO3
Na2CO3

Nb2O5
LiNbO3
Zr ballethyl alchol 24hr
Ball milling
Calcining
850 ? 2 hrs
Measurements

• Crystal structure (XRD)
• Surface morphology (SEM)
• Dielectric properties 1kHz1MHz(HP4192A)
• Piezoelectric properties (HP4194a, d33 meter)
• P-E hysteresis loop (Sawyer-Tower circuit)
• dc conductivity (KEITHLEY237)

Ball milling
Sintering
1075? 2 hrs
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SEM Images of NKN-LN Ceramics
NKN
0.98NKN-0.02LN
0.96NKN-0.04LN
0.95NKN-0.05LN
5 mm
0.94NKN-0.06LN
0.92NKN-0.08LN
0.90NKN-0.10LN
Grain sizes of NKN-LN ceramics were increased
with increasing LiNbO3 concentration.
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XRD Patterns of NKN-LN Ceramics
(1-x)Na0.5K0.5NbO3-xLiNbO3
Tetragonal
MPB
Orthorhombic
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Lattices Parameters of NKN-LN Ceramics
Å
The structure changes from orthorhombic to
tetragonal symmetry. MPB between orthorhombic and
tetragonal phase exists at 0.05ltxlt0.08.
MPB
Tetragonal
?
Orthorhombic
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Temperature Dependence of Dielectric Constant and
tand for NKN-LN Ceramics
MPB
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dc Conductivity of NKN-LN Ceramics
(1-x)Na0.5K0.5NbO3-xLiNbO3
Potassium has relatively low melting points
compared to those of other elements. So,
potassium is vaporized easily during the process
of the high-temperature treatment. The loss of
potassium causes many defects such as potassium
vacancies and oxygen vacancies. Therefore, NKN
ceramics exhibited a high dc conductivity. The
substitution of LiNbO3 in the NKN could reduce
conductivity.
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P-E Hysteresis Loops of NKN-LN Ceramics
Polarization (mC/cm2)
(1-x)Na0.5K0.5NbO3-xLiNbO3
Cannot saturate
Electric Field (kV/cm)
The P-E loops of NKN and 0.98NKN-0.02LN ceramics
show leaky behavior whereas that of
0.95NKN-0.05LN ceramics are well saturated. The
substitution of LiNbO3 in the NKN could improve
ferroelectric properties.
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d33 and kp of NKN-LN Ceramics as a function of
LiNbO3 Concentration
(1-x)Na0.5K0.5NbO3-xLiNbO3
The maximum value of d33 was obtained at x0.05
which is belonging to MPB region. The mechanical
coupling coefficient, kp also has similar trend.
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Summary

• We have fabricated (1-x)Na0.5K0.5NbO3-xLiNbO3
  (x00.1) ceramics and investigated their
  ferroelectric and piezoelectric properties as
  function of LiNbO3 concntration.
• The structural phase transition from orthorhombic
  to tetragonal structure occurred at the
  composition range of x0.050.08.
• At the morphotropic phase boundary composition of
  x0.05, NKN-LN ceramics showed the highest values
  of kp (34.5) and d33 (172 pC/N).
• The substitution of LiNbO3 (0.05 mol) in the NKN
  could reduce conductivity and improve
  ferroelectric properties.

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