Gas-tight proton-conducting Nd2 − xCaxZr2O7 − δ (x = 0, 0.05) ceramics

Fluorite-based proton conducting oxides: structures, materials and applications

“…The proton conductivity of (Nd 0.975 Ca 0.025 ) 2 Zr 2 O 7− δ was approximately 7.0 × 10 −5 and 2.5 × 10 −4 S cm −1 at 500 and 600 °C, respectively. 101 As has been mentioned, by using La to occupy the A-site, the resulting La 2 Zr 2 O 7 system also exhibits proton conduction, and the highest proton conductivity was reported for (La 0.975 Ca 0.025 ) 2 Zr 2 O 7− δ to be 6.8 × 10 −4 S cm −1 at 600 °C. 81 Interestingly, one may notice that the proton conductivity increases in the sequence of Gd 2 Zr 2 O 7 < Sm 2 Zr 2 O 7 < Nd 2 Zr 2 O 7 < La 2 Zr 2 O 7 , in agreement with the increasing eight-coordinated cation radius of Gd 3+ (1.053 Å) < Sm 3+ (1.079 Å) < Nd 3+ (1.109 Å) < La 3+ (1.160 Å).…”

“…The proton conductivity of (Nd 0.975 -Ca 0.025 ) 2 Zr 2 O 7Àd was approximately 7.0 Â 10 À5 and 2.5 Â 10 À4 S cm À1 at 500 and 600 1C, respectively. 101 As has been mentioned, by using La to occupy the A-site, the resulting La 2 -Zr 2 O 7 system also exhibits proton conduction, and the highest proton conductivity was reported for (La 0.975 Ca 0.025 ) 2 Zr 2 O 7Àd to be 6.8 Â 10 À4 S cm À1 at 600 1C. 81 11 These results indicate that the size of the A-site cation has a significant effect on the proton conduction of pyrochlore zirconates.…”

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

“…La2(Hf1.9La0.1)O6.95 "stuffed" hafnate pyrochlores demonstrated proton contribution ~1× 10 −5 S/cm at 600 °C, whereas the conductivity of Ca-doped zirconate pyrochlores is higher by ~1-1.5 orders of magnitude. For example, the conductivity of (La2−xCax)Zr2O7−δ (x = 0.05) in wet air is 7 × 10 −4 S/cm at 600 °C while that of (Nd2-xCax)Zr2O7-δ (x = 0.05) is 2.5 × 10 −4 S/cm at 600 °C) and that of (Sm2−xCax)Zr2O7−δ (x = 0.05) is 7.5 × 10 -4 S/cm at 600 °C [41][42][43][44][45]. The comparison of the proton conductivity of the Ca-doped zirconates and "stuffed" hafnate pyrochlores indicates that the higher basicity of cations around an oxygen vacancy in position 48f as a result of Ca-substitution, a more basic cation, for the lanthanide increases the hydration at this position and, as a result, proton conductivity rises by almost two orders of magnitude [41][42][43][44][45][46][47][48].…”

“…For example, the conductivity of (La2−xCax)Zr2O7−δ (x = 0.05) in wet air is 7 × 10 −4 S/cm at 600 °C while that of (Nd2-xCax)Zr2O7-δ (x = 0.05) is 2.5 × 10 −4 S/cm at 600 °C) and that of (Sm2−xCax)Zr2O7−δ (x = 0.05) is 7.5 × 10 -4 S/cm at 600 °C [41][42][43][44][45]. The comparison of the proton conductivity of the Ca-doped zirconates and "stuffed" hafnate pyrochlores indicates that the higher basicity of cations around an oxygen vacancy in position 48f as a result of Ca-substitution, a more basic cation, for the lanthanide increases the hydration at this position and, as a result, proton conductivity rises by almost two orders of magnitude [41][42][43][44][45][46][47][48]. Another factor contributing to the decrease in the conductivity of the "stuffed" hafnate pyrochlores is the presence of more covalent and strong Hf-O bonds in hafnates relative to zirconates [32].…”

Membrane Technologies for Decarbonization

“…In this regard, attempts are being made to create similar materials containing no alkaline earth metals. Among them are promising systems based on complex oxides of lanthanum with titanium, zirconium, tin, cerium, or niobium [249][250][251][252], as well as lanthanum oxides with trivalent elements LaXO 3 with a perovskite structure [253][254][255]. However, the practical application of these materials is currently constrained by the relatively high ohmic losses of FCs based on them [256][257][258].…”