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1 Journal of the Korean Ceramic Society Vol. 48, No. 4, pp. 323~327, DOI: /KCERS Electrical Properties and Temperature Stability of Dysprosium and Erbium Co-doped Barium Titanate with Perovskite Structure for X7R MLCCs Taimin Noh, Jinseong Kim, Jiseung Ryu*, and Heesoo Lee School of Materials Science and Engineering, Pusan National University, Busan , Korea *National Core Research Center, Pusan National University, Busan , Korea (Received June 8, 2011; Resived July 6, 2011; Accepted July 22, 2011) Dysprosium Erbium ƒ X7R MLCC r e p BaTi» p k Á½ Á *Á w œw * w w ƒw l ( ; ; ) ABSTRACT The effects of Dy 2 and Er 2 co-doping on electrical properties and temperature stability of barium titanate (BaTi ) ceramics were investigated in terms of microstructure and structural analysis. The dielectric constant and the insulation resistance (IR) of 0.7 mol% Dy 2 and 0.3 mol% Er 2 co-doped dielectrics had about 60% and 20% higher than the values of undoped one, respectively, and the temperature coefficient of capacitance (TCC) met the X7R specification. The addition of Dy 2 contributed to electrical properties caused by increase of tetragonality; however, preferential diffusion of Dy 3+ ions toward A site in BaTi grain exhibited an adverse effect on temperature stability by grain growth. On the other hand, The Er 2 addition in BaTi could affect the TCC behavior and the IR with suppression of grain growth caused by reinforcement of grain boundary and electrical compensation. Therefore, the enhanced electrical properties and temperature stability through the co-doping could be deduced from the increase of tetragonality and the suppression of grain growth. Key words : BaTi, Dysprosium, Erbium, Electrical properties, Temperature stability 1. { m»» w y»» x y xy t w w š š w t j ƒwš. p, ps t»» {»» v t dx fq l (MLCC : Multilayer Ceramic Capacitor) j ƒwš, t xy š y w w š. 1-3) MLCC dx ü dw» w w d,, wš Corresponding author : Heesoo Lee heesoo@pusan.ac.kr Tel : Fax : Ì w. š MLCC xw» w Ì w ù d ƒ g w. w x ¾ y d y š Ì 0.6 µm, ü d Ì 0.5 µm š MLCC ƒ z» w w dy w w w» w ƒ w š. t, œ w MLCC ƒ š ù w w œ š. fq l p xw» w dopant ƒw w š p, t w ƒ m w p w w y š. 2-6) m BaTi ƒ Ba siteù Ti site eyw ƒƒ l w 323

2 Dysprosium Erbium ƒ X7R MLCC r e p BaTi» p y 12 sw w ù core-shell x, w w. w, w m ƒ v w ƒƒ w w» p y w e w q w p x w» w ƒ w. p w, ƒ w» BaTi w MgO, MnO 2, m (Dy 2, Ho 2, Sm 2 ), (V 2 O 5, SiO 2 ) ƒw ù» v ƒw p w g šƒ. w 2,4,5) ƒ mw w z w w BaTi ü m v mw p w ƒ v w. ƒ w w, ey w w wƒ w ù, l ey w y w wƒ wš ww. MLCC BaTiü m ƒ w, Dy 2 w j» wù y j Er 2 j» w š., mw w w» p w j» w Dy 2 Er 2 ƒw X7R( 55 o C to 125 o C, C= ± 15% or less) j MLCC ƒ w ww. Dy 2 Er 2 ƒ w y z y wš, ƒ w d w t x mw w w w, mw y w tetragonality d w p ³ w. 2. x x w t ƒ Dy 2 Er 2 kw y r w. BaTi (Samsung Fine Chemicals, sbt-03, mean particle size : 200 nm) w 1.0 mol% MgO (Aldrich, 98%), 0.05 mol% V 2 O 5 (JunseichemicalCo. Ltd, 99.0%), 1.5 mol% SiO 2 (Aldrich, 99.9%), 0.05 mol% MnO 2 (Aldrich, 99%) ƒ kw. š r w ƒ m ƒ w p 0mol% 1mol%¾ Dy 2 (Aldrich, 99.9%) Er 2 (Aldrich, 99.9%) ƒw. r w» w, w ywwš g ball k w 24 w. yw 70 o C» 24 g 100 µm sieve w ³ w ü. disk xk xw» w PVA ƒw yw z w ³ w w. 20Φ Disk 150 MPa ƒ x w x r N 2 y»» 1320 o C, 2. w,» p sƒ w r t Ag paste screen printing w 750 C o w. Ag s r w LCR meter (Agilent, E4980A) w 1 khz/1.0 V (dielectric constant) d w, p (TCC : temperature coefficient of capacitance) y w» w EIA specification X7R» w w» ü 55 o C~125 o C d w. w, sƒw» w high resistance meter (Agilent, 4339B) w 100 V, 60 ƒw z w(ir : insulation resistance) d w. j»ƒ» p e w» w FE-SEM (Field Emission Scanning Electron Microscope, Hitachi-S4800) w. m ƒ v BaTi tetragonality» p š w» w X-Ray Diffraction (M18XHF, MAC Science) w BaTi w š z ql w Rietveld refinement method mw c/a tetragonality w ƒ BaTi sƒw. 3. š Fig. 1 Dy 2 Er 2 ƒ ƒ BaTi r p» w 55 o C~150 o C d w TCC l. m ƒ vw BaTi r Dy 2 vw r y w. 0.7 mol% Dy mol% Er 2 ƒw ƒ p ùkü ƒ 60% ƒ š, w TCC p X7R» k (Fig. 1(a)). Dy 2 ƒ ƒw w š 1.0 mol% Dy 2 ƒw ƒ, Er 2 ƒ ƒ r w., Fig. 1(b) Er 2 ƒ ƒ 4 X7R g ƒ ƒw. Dy 2 Er 2 ƒ r w Fig. 2 ùkü. 0.7 mol% Dy mol% Er 2 ƒw Ω ƒ w ƒ r w wz

3 325 k Á½ Á Á Fig. 1. Variation in (a) dielectric constant and (b) temperature coefficient of capacitance (%) of BaTi specimens undoped and doped with Dy 2 and Er 2 as a function of temperature. Fig. 2. Variation in insulation resistance of BaTi specimens as a function of Dy 2 and Er 2 contents. w 20% ùkü., Dy 2 ƒw r û w ùkü p w w w w, w w p BaTi w. 7) m ƒ BaTi» p» w t x w. Fig. 3 z r ƒ y SEM w. ƒ ü w, grain boundary w grain w w grain w grain y š š. 8,9) BaTi j» w w» w, ú w öe. ƒ 10) r ù (Fig. 3(a)), Er 2 ƒ w j»ƒ 0.3~0.4 µm (Fig. 3(b-e)). w Dy l 3+ w w A site y ey wš j w» w l 3+ Er B site eyw y w g w e. 11,12), Dy 2 ƒ r grain boundary y w ùƒ w 1.2 µm j» w. 5), BaTi ƒƒ w w, j» y w Fig. 1(b) ùkù w p Fig. 2 ù kù p q w. Fig. 4 m ƒ w XRD d. Fig. 4(a) ùkù, ƒ XRD peak BaTiƒ y ƒ, m ƒ 1mol% ƒ p p w y y x q. m BaTiü ƒ yƒ e w» w Rietveld refinement w lattice parameter y mw tetragonality w. Rietveld tetragonality y m w m ƒ c/a lattice paramater Fig. 5 ùkü. Dy 2 w ƒw lattice parameterƒ wù a y w. c/a, Dy 2 w ƒ Er 2 w tetragonalityƒ ƒw. 48«4y(2011)

4 Dysprosium Erbium ƒ X7R MLCC r e p BaTi» p 326 Fig. 3. Morphology of the surface of undoped and co-doped BaTi specimens : (a) undoped, (b) 1 mol% Dy 2, (c) 0.7 mol% Dy 2 and 0.3 mol% Er 2, (d) 0.5 mol% Dy 2 and 0.5 mol% Er 2, (e) 0.3 mol% Dy 2 and 0.7 mol% Er 2, and (f) 1 mol% Er 2. Fig. 4. XRD patterns of undoped and co-doped BaTi specimens : (a) undoped, (b) 1 mol% Dy 2, (c) 0.7 mol% Dy 2 and 0.3 mol% Er 2, (d) 0.5 mol% Dy 2 and 0.5 mol% Er 2, (e) 0.3 mol% Dy 2 and 0.7 mol% Er 2, and (f) 1mol% Er 2 Fig. 5. Tetragonality and lattice parameter of Dy 2 and Er 2 co-doped BaTi specimens. w wz BaTi tetragonalityƒ ƒw e ƒ p w j w. BaTi w ƒ tetragonality ƒ w» w y w j w öe., Er 2 ƒ grain boundary y mw w w p w» w., ƒ mw y z w MLCC BaTi» p w» w q. 4. Dy 2 Er 2 ƒ r e p ƒ X7R MLCC BaTi» p w w. m ƒ w w 1mol% ƒ» w, BaTi Er 2 ƒw w p t w d š w. Dy 2 w ƒw w 1mol% ƒ w, 80 o C 2900 ƒ y w w ùkü., Er 2 ƒw r w, p 0.7 mol% Dy mol% Er 2 ƒw r ƒ w 60% ƒ X7R w. m ƒ w p y w, w w ùkû Dy 2 ƒw ƒ û wp ùk ü. Dy 2 ƒ BaTi tetragonality w e ƒ ƒ» wù, grain boundary Dy y w 3+

5 327 k Á½ Á Á» g w., Er 2 ƒ BaTi ü grain boundary y w g w ƒ w» w. BaTi Er 2 ƒ w,» p X7R j p y z y w. Acknowledgment t» w (B ) w. REFERENCES 1. H. Kishi, Y. Mizuno, and H. Chazono, Base-metal Electrodemultilayer Ceramic Capacitors: Past, Present and Future Perspectives, Jpn. J. Appl. Phys., (2003). 2. J. Nichikawa, T. Hagiwara, K. Kobayashi, Y. Mizuno, and H. Kishi, Effects of Microstructure on the Curie Temperature in BaTi -Ho 2 -MgO-SiO 2 System, Jpn. J. Appl. Phys., (2007). 3. D. Y. Lu, M. Toda, and M. Sugano, High-permittivity Double Rare-earth-doped Barium Titanate Ceramics with Diffuse Phase Transition, J. Am. Ceram. Soc., (2006). 4. D. Makovec, Z. Smardzija, and M. Drofenik, Solid Solubility of Holmium, Yttrium, and Dysprosium in BaTi, J. Am. Ceram. Soc., (2004). 5. K. J. Park, C. H. Kim, Y. J. Yoon, S. M. Song, Y. T. Kim, and K. H. Hur, Doping Behaviors of Dysprosium, Yttrium and Holmium in BaTi Ceramics, J. Eur. Ceram. Soc., (2009). 6. Y. Tsur, A. Hitomi, I. Scrymgeour, and C. A. Randall, Site Occupancy of Rare-earth Cations in BaTi, Jpn. J. Appl. Phys., (2001). 7. X. H. Wang, R. Z. Chen, Z. L. Gui, and L. T. Li, The Grain Size Effect on Dielectric Properties of BaTi Based Ceramics, Mater. Sci. Eng., B (2003). 8. R. Kirchheim, Grain Coarsening Inhibited by Solute Segregation, Acta Mater., (2002). 9. E. Rabkin, On the Grain Size Dependent Solute and Particle Drag, Scripta Mater., (2000). 10. G. A. Samara, The Relaxational Properties of Compositionally Disordered AB Perovskite, J. Phys., 15 R367-R411 (2003). 11. Y. Pu, W. Chen, S. Chen, and Hans T. Langhammer, Microstructure and Dielectric Properties of Dysprosium-doped Barium Titanate Ceramics, Ceramica, (2005). 12. D. Y. Lu, X. Y. Sun, and M. Toda, A Novel High-k Y5V Barium Titanate Ceramics Co-doped with Lanthanum and Cerium, J. Phys. and Chem., (2007). 48«4y(2011)