Microstructure and impedance spectroscopy of high density holmium hafnate (Ho2Hf2O7) from nanoparticulate compacts

Proton Conductivity of La2(Hf2−xLax)O7−x/2 “Stuffed” Pyrochlores

“…The Ln 2 Hf 2 O 7 (Ln = Dy, Y, Ho, Yb) heavy RE hafnates have a fluorite structure, and the Dy-and Ho-based compounds have the highest conductivity among them [8]. These results were essentially confirmed by Sardar et al [9], who were able to separate the total conductivity onto the bulk (1.0 × 10 −4 S/cm at 700 • C) and grain boundary (4.66 × 10 −5 S/cm at 700 • C) components for the Ho 2 Hf 2 O 7 fluorite prepared by the conventional solid-state reaction technique. Recently, Shlyakhtina et al [16] synthesized Eu 2 (Hf 2−x Eu x )O 7−x/2 (x = 0.1) stuffed pyrochlores, which showed the highest oxygen ion conductivity among the hafnate family: ~7.5 × 10 −4 S/cm at 700 • C. This is, however, lower than the conductivity of the RE zirconates and titanates [16][17][18][19][20].…”

“…The (Ln = La-Lu; M = Ti, Zr, Hf) systems with a pyrochlore structure can be used as potential oxygen ion-conducting electrolytes for solid oxide fuel cell (SOFC) applications [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. The most promising electrolytes among pyrochlores are rare-element (RE)-based zirconates: the Li-doped gadolinium zirconate Gd 1.7 Li 0.3 Zr 2 O 6.7 , with a conductivity of 1 × 10 -3 S/cm at 450 • C (~8 × 10 -3 S/cm at 700 • C) [1], and (Nd 2−x Zr x )Zr 2 O 7+x/2 (x = 0.4) (1.78 × 10 −2 S/cm at 700 • C) [5].…”

“…Such anion Frenkel pair (V •• O + O i ) defects are the most stable ones in pure La 2 Hf 2 O 7 . It is worth noting that, whereas the oxygen ion conductivity of the RE hafnates and related solid solutions has been the subject of intense research [8][9][10][11][12][13][14][15][16], there are few data on their proton conductivity, except for the Nd 2 (Hf 2−x Nd x )O 7−x/2 (x = 0; 0.1) system [22].…”