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1 Jurnal f the Krean Ceramic Sciety Vl. 44, N. 12, pp. 683~689, Grain-Bundary Cnductin in Slid Oxide Electrlyte Jng-Heun Lee Department f Materials Science and Engineering, Krea University, Seul , Krea (Received Octber 31, 2007; Accepted Nvember 15, 2007) y š w š w œw ( ; ) ABSTRACT Grain-bundary cnductin in the flurite-structure slid xide electrlytes such as acceptr-dped zircnia and ceria were reviewed. The siliceus impurity, even several hundreds ppm, affects the inic cnductin acrss grain bundary t a great extent. Varius appraches t imprve grain-bundary cnductin in flurite-structure xide electrlytes have been investigated, which include (1) the scavenging f siliceus phase by the reactin with secnd phase, (2) the gathering f intergranular siliceus phase int a discrete cnfiguratin and (3) the dewetting f intergranular liquid phase by pst-sintering heat treatmtent. key wrds : Grain-bundary cnductin, Slid xide electrlyte, Scavenging, Irnpedance spectrscpy, Slide xide fuel cell 1. y š w y (SOFC, slid xide fuel cell), 1) rv,»yw ƒ 2) y š. yz š,»yw ƒ û» w ƒ w v w. x SOFC»yw ƒ š t š w y g y, g û ƒ l Zr 4+ Ce eyw w 4+ (xgyen vacancy)ƒ. 2ZrO 2 X. A 2 2A zr ' + 3O O +V Ȯ (1) 2CeO 2 X. B 2 2B Ce ' + 3O O +V Ȯ (2) š w w ü w, w, w ù. w w ü w w ww,» w ü w w ù š. ü w w l Crrespnding authr : Jng-Heun Lee jngheun@krea.ac.kr Tel : Fax : ƒ w.» w Zr 4+, Ce eyw y ƒw, Zr Ce w ƒw w š š. l y ey w w strain ƒ w» w š. lƒ ƒ z w l z w ƒ w w(defect assciate) x w û š. g w Yb 2, Sc 2 ƒ ƒ, CeO 2 w Gd 2, Sm 2 ƒ ƒ ƒƒ ùkü. ù, g ƒ ƒ ƒ w p y g (YSZ, Yttria-Stabilized Zircnia)ƒ ƒ š. y w ü w x. 3) w Bauerleƒ4) 2 g š w w w ü z x ¾ y š. q ã ƒ d w v ü z.,,, e w z w w 683

2 684 Fig. 1. Tw rigins f grain-bundary resistance in plycrystalline slid electrlyte: (a) the depletin f xygen vacancy and (b) siliceus intergranular phase. w. x g š w w C û w, ƒ û œvd w 5,6) Si sww š w ù š. 7,8) (Fig. 1) w w w w, z sww w w ƒƒ wš. p Si 100 ppm ƒ w 100 ƒw, Si sww d w r (sub-mnlayer segregatin)d x ù 1-2 nm Ì x» w š. 9) SiO 2 ƒ w y œ y. SOFC ƒ p w SiO 2 w w. 10), œvd w w j, Si w z w ƒ w. š g š w w j s w j ƒ š» r. 2. g y š w ƒz Fig. 2 y š w ƒ ƒz ù kü. ƒz ƒ ü w - ƒ w ü w wš ü ƒ. ü RC z RC z ƒ, t CaF 2. ƒ 11) z ƒ, j Fig. 2. Schematic diagram f xygen in cnductin in xide slid electrlyte and crrespnding equivalent circuits.»ƒ ù j» ƒ ƒw x ùkü. ƒz w ü w w - j. w j, mw w j., ü mw ƒ ù š, w w š w ù. ƒ» w š w., ü RC z RC z ƒ ƒz w. g š w w ü w 100-1,000 j š š 12) ƒz ww w., Ì, wetting, j w e w. g š w j»ƒ µm, ̃ nm, ƒ ü w sp w 1,000 j š ƒ w (ρ gb 1000ρ gi ), R=ρ(l/A) l ü w(r gi ) w(r gb ) w ƒ. ü j ƒ š ƒ w C=ε 0 ε r (A/d) l ̃ 1/1,000 ƒ ü w eq l ƒ 1,000 j (C gb 1,000C gi )., (R gb C gb ) ü (R gi C gi ) 1,000 ƒ v ƒ q y. 3. g y š w 3.1. Scavenging w w y g w j» w Fe 2, 12) Bi 2, 12) TiO 2, 13) 12-23) ƒ ƒ w wz

3 . ƒ w j z ƒ š, 15-20) ƒ ƒ ƒ û š. 12,21,23) (1) ƒ r SiO 2 sw ƒ š, (2) ƒ ƒ y g š, (3) y SiO 2» q. ppm w SiO 2 ƒ sw š ƒ 1600 C w 1-20 ml% ù ƒw ƒ w ùkü, 15-19) ƒ C š ml% ùƒ ƒ ƒ w. 21,23) Gödickemier 14) wt% SiO wt% ƒ y gƒ w d w, ƒ SiO 2 w ƒ ƒ š šwš, l SiO 2 ƒ š w w š w. 500 ppm SiO 2 sw 15 ml% CaO y g (15CSZ) 4µm 10 µm 1ml% ƒw z C wš w. 24) 1525 C w ƒ 15 ƒw, 1575 C w ƒ 30-50% w. w š ƒ š w CaO-SiO 2 - s ww š w x w y. y w CaO w. w, SiO ppm ü ƒ w r (segregatin) w š w w. Aki š 15CSZ w 9) STEM mw Si r dr (mnlayer segregatin) 10% w ü w w 100 f. TEM Si r w w f w. SiO 2 ƒ ppm ƒ, Si sww w»ƒ š, ƒƒ SiO 2 sw š w w x»., ƒ SiO 2 scavenging w w». Butler Drennan 20) Y 2 /Yb 2 y g ù ƒw z TEM ww, ü ù Zr-sw (Zr + Si)-sw inclusin wš, w y š w 685 ù Si Al t w cusp š šw. ù ƒ Si scavengingw, v yƒ w ù yƒ w j» w ùkù. 14) 100 ppm SiO 2 sww 8YSZ 1ml% ƒw z v y w ƒ y w z, ppm ¾ mapping ƒ w imaging SIMS (Secndary In Mass Spectrscpy)» w r ü SiO 2 e w. ƒ ƒ r SiO 2 r y w, ƒ ƒ SiO 2 scavenging x y w. ƒ š w SiO 2 scavengingw w x. z ù j» 0.3, 4, 10 µm y j š, ƒ 0.2, 1 ml% yw z scavenging z y w. x w 25) ƒw µm ¼ wš w z w ƒw ùkû. x Si sww mw y w» w. Butler Drennan ü 20) ƒ Zr-sw (Zr + Si)-sw inclusin ƒ š š w, ƒ y Si w w w., g š w Si sw mw y q. Fig. 3(a) ù ƒ w š w scavenging ùk ü w w ƒw wš z., ƒw z w ƒ g ü š ƒw, ü ƒ û ƒ w. (Fig. 4) x Miyayama 21) Feighery šwš 17), Al Zr '-.... V O w w (-143 kj/ml)ƒ Y Zr '-V O w w (-39 kj/ml) û ƒ 26) w w w., ù ƒ w ƒ ù ƒ w ü ƒ ƒ j» ƒ w. 44«12y(2007)

4 686 Fig. 3. Schematic diagram f (a) additive scavenging and (b) precursr scavenging. Fig. 4. Schematic diagram f impedance change by the incrpratin f int YSZ lattices. w w» w ù ƒw š y g w w w. 120 ppm SiO 2 sww 8YSZ(8 ml% Yttria Stabilized Zircnia) r 1200 C 10 1 w z 1500 C w, ù ƒw š 7 w k. w 27) ù ƒw w, 1200 Cƒ ƒ, 10 ƒ v w. ù ƒ ƒw š (precursr) scavenging ùkü w x precursr scavenging w.» x ³ w» w 100 ppm Si w ù f, x. x mw ZrSiO 4 x scavenging» š q w. ZrSiO 4 y y ƒ 28)»., ZrO 2 SiO 2 yw C š k ZrSiO 4, ZrO 2 SiO 2ƒ sw. 28) wt% ZrSiO 4 seed ƒw z w ZrSiO 4, 29-31) ZrSiO 4ƒ epitaxial» w. Mri 29) ZrSiO 4 w ƒ 1200 C šw, ew., 1200 C 8YSZ r w ZrSiO 4 w š, z š ZrSiO 4 w w w SiO 2 (discrete) y j q. (Fig. 3(b)) w ZrSiO C w, 28) C ZrSiO 4 w š z w k q. 2 w w z w» w 80, 170 ppm SiO 2 sww 8YbSZ(8 ml% Ytterbia Stabilized Zircnia) r w š x y w. 32) x ƒ 1250 C 8YSZ wš, 10 ƒ v w ùkû. 2 w w y g. 2 w, SiO 2 ¾ scavenging w w. 33) 8YSZ r sw SiO 2 100, 160, 310, 1000 ppm w z 1200 C 40 1 wš, C 4 w r w. SiO 2 ƒ 160 ppm w 2 w ƒ 5 w, SiO 2 ƒ 300 ppm 2 w ƒ w. precursr scavenging SiO 2 ƒ z w. 3.3 Dewetting w w 15CSZ r r sw SiO 2 w û CaO-SiO 2 - x w. 34,35), w j w e. w 36), wetting yw. wetting w. 15CSZ r (1) 1550 C 4, (2) w wz

5 1300 C C 4, (3) 1550 C C 10 3ƒ w z v d w. x y j, z 1300 C 10 w ƒ 7 ƒw. TEM z w dewetting y w. ƒ (dihedral angle, φ). = φ γ g 2γ SL cs-- 2 γ g, γ SL ƒƒ š (slid-liquid). y γ SL w š - š γ SS' ë š, γ SS' γ SL j, y ƒ 37) ƒw dewetting ù q.,» z ƒ, z w ƒ w w. (Fig. 5) 4. y š w 4.1. Scavenging w w GDC(Gd 2 -dped CeO 2 ) SDC(Sm 2 -dped CeO 2 ) t š w Siƒ sw w - ƒ š š š ) ù, š w w j g š w w š ü. Lane 42) ppm SiO 2 sww GDC r CaO SrO 1-2 ml% ƒw z 1450 C w ƒ j s w x šw. š w w w ƒ w. Lane SEM Ca Siƒ l CaOƒ SiO 2 w scavenging w š q w. 43) 500 ppm SiO 2 sww GDC 2 ml% CaO ƒw ƒ 50 w y w. 2ml% CaO ƒw GDC r X- z 2 Fig. 5. Dewetting f intergranular phase by crystallizatin. y š w 687 (3), SEM w». CaOƒ CeO 2 ü š w, ƒ 1500 C Lane 42) wù q. TEM w CaO ƒw ƒ faceting w w. ƒ facet ƒ w (cherency)ƒ f w, SiO 2 sww r ù ƒ w ƒ š w. š CaOƒ SiO 2 w scavenging g ƒ w. 44) 500 ppm SiO 2 sww GDC x Sr-acetate w ww z, w š 1500 C w. r w 7 mm, 7.5 mm, Ì 0.9 mm r. j» 0.5 2mm mm 8 w z 1100 C w. w Sr y v d w. d Sr ƒ ƒ 120 w w. SrO ƒ w GDC ƒ w w. 45) GDC w j scavenger MgO w. CaO SrOƒ ü š w, MgO ü š. 8 Ca 2+, Sr j» ƒƒ Å, 1.25 Å Gd 3+ (1.06 Å), Ce 4+ (0.97 Å) w j. 46) 8 2+ Mg 0.89 Å 4+ Gd 3+, Ce w. interstice j» ƒw š», interstice j» j š w. ƒ q w» ƒ y»., MgO CaO, SrO ƒ 2 w. 500 ppm SiO 2 sww GDC r 0.3 ml% MgO ƒw ƒ 45 ƒw. EELS EBSD w š š MgOƒ w SiO 2 w Mg 2 SiO 4 x w y w. SiO ppm ml% w Mg 2 SiO 4 x w» w MgO ml%. x 0.3 ml% ew, SiO 2 mw y w MgO wš Mg 2 SiO 4 x w q z w w 47) 500 ppm GDC 2 w 44«12y(2007)

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