Effect of La substitution for Gd in the ionic conductivity and oxygen dynamics of fluorite-type Gd₂Zr₂O₇

Abstract

We have prepared different compositions in the Gd 2−y La y Zr 2 O 7 solid solution by mechanically milling stoichiometric mixtures of the corresponding oxides. Irrespective of their lanthanum content, as-prepared powder samples consist of single-phase anion-deficient fluorite materials, although the long-range ordering of cations and anion vacancies characteristic of pyrochlores was observed for y 0.4 after post-milling thermal treatments at 1200 • C. Ionic conductivity was found to be thermally activated and almost independent of La content for 0 y 1, since the pre-exponential factor decreases as structural ordering increases; however, there is a concomitant decrease of the activation energy E dc for oxide-ion diffusion, from E dc = 1.13 ± 0.02 eV for the anion-deficient fluorite Gd 2 Zr 2 O 7 to E dc = 0.85 ± 0.03 eV for the partially ordered pyrochlore-type Gd 1.2 La 0.8 Zr 2 O 7 . Electrical conductivity relaxation is well described by a Kohlrausch-Williams-Watts (KWW) function of the form = exp(−(t/τ ) 1−n ), where the fractional exponent n decreases as the La content (ordering) increases. These results are explained in terms of weaker ion-ion interactions in the better ordered structure and highlight the importance of structural ordering/disordering in determining the dynamics of mobile oxygen ions.

Electrical conductivity of samarium–ytterbium zirconate ceramics

“…Enormous amounts of efforts were found in the literature to improve electrical conductivity of oxide electrolyte materials [7][8][9][10]. In recent years, new rareearth zirconates with various ionic radius ratios of r(Ln 3+ )/r(Zr 4+ ) are of considerable scientific interest [11][12][13][14]. Mandal et al [11] found that a significant increase in electrical conductivity was obtained at 622-696 K by properly doping at the Gd site with isovalent rare-earth cations like Nd in Gd 2 Zr 2 O 7 ceramic.…”

“…Mandal et al [11] found that a significant increase in electrical conductivity was obtained at 622-696 K by properly doping at the Gd site with isovalent rare-earth cations like Nd in Gd 2 Zr 2 O 7 ceramic. Diaz-Guillen et al [12,13] metric elemental oxides, and found that electrical conductivity of (Gd 1 − x La x )Zr 2 O 7 (0 ≤ x ≤ 0.4) ceramics was almost La-content independent in the temperature range of 773-1023 K. The conductivity of pyrochlore-type Sm 2 Zr 2 O 7 was comparable to those of other good conductors such as yttria-stabilized zirconia in lowtemperature regions [3]. (Sm 1 − x Gd x ) 2 Zr 2 O 7 (0 ≤ x ≤ 1.0) ceramics were synthesized by pressureless-sintering method, and the highest electrical conductivity was obtained for SmGdZr 2 O 7 in the temperature range of 623-873 K [14].…”

Improvement of Electrical Conductivity of Trivalent Rare‐earth Cation‐doped Neodymium Zirconate by Co‐doping Gadolinium and Ytterbium

“…Currently, 8 mol-% Y 2 O 3 -ZrO 2 (YSZ) is used as a solid electrolyte in conventional SOFCs, while anode and cathode materials are Ni-YSZ cermets and La 1-x Sr x MnO 3 oxide, respectively [4][5][6]. However, when SOFCs are operated at high temperatures for a long time, unwanted reactions at the cathode/electrolyte interface will generate insulating zirconates (La 2 Zr 2 O 7 and SrZrO 3 ), which may have a detrimental effect on SOFCs performance [7,8]. Pyrochlore oxides of A 2 Zr 2 O 7 -type (A = lanthanide) structure show excellent electrical properties owing to high compositional diversity, structural flexibility and intrinsic concentration of oxygen vacancies [9][10][11].…”

“…The dual Yb+Gd intermix doping causes a distinctly enhanced total conductivity as compared to unmodified Nd 2 ) [7,8,[18][19][20]. Díaz-Guillén et al [7,8] found that electrical conductivity of Gd 2-x La x Zr 2 O 7 (0 ≤ x ≤ 1.0) ceramics was almost La-content independent in the temperature range of 773-1,023 K. A significant increase in electrical conductivity is found by suitable substitution of isovalent rare-earth cations like Nd at the Gd site in Gd 2 Zr 2 O 7 from 622 to 696 K [18]. For (Nd 1-x Yb x ) 2 Zr 2 O 7 (0 ≤ x ≤ 1.0) ceramics, electrical conductivity of pyrochlore-type materials is clearly higher than that of defect fluorite-type materials in the temperature range of 723-1,173 K [19].…”

The influence of pentavalent Nb substitution for Zr on electrical property of oxide-ion conductor Gd2Zr2O7

“…In the family of pyrochlore-type compounds, Gd 2 Zr 2 O 7 had the highest intrinsic ionic conductivity (10 −3 S cm −1 at 1000 K) at the intermediate temperature as compared with commercially used electrolytes [11]. During the past decades, Gd 2 Zr 2 O 7 doped with different cations has been widely investigated as potential electrolyte materials for intermediate temperature SOFCs [12][13][14][15][16][17][18]. (Gd 0.5 Nd 0.5 ) 2 Zr 2 O 7 exhibited a significant enhancement in ionic conductivity at 622-696 K as compared with pure Gd 2 Zr 2 O 7 [12].…”