Alkali metals as efficient A-site acceptor dopants in proton conducting BaZrO₃

Abstract

In the present contribution, we assess the efficiency of the alkali metals (Na, K, Rb and Cs) as A-site acceptor dopants in proton conducting BaZrO 3 by first principles calculations. The calculated acceptor-proton complexes become weaker with increasing dopant size, with binding energies ranging from À0.33 eV for Na to À0.10 eV for Cs, which is in the range of, or even lower than, those found for B-site doped BaZrO 3 . By mapping out all relevant minimum energy pathways for the proton, we reveal that the highest migration energy barrier for most of the alkali metals is comparable or even lower than that of Y.Further, all A-site dopants display more exothermic hydration enthalpies compared to that of Y-doped BaZrO 3 , ranging from À131 kJ mol À1 to À83 kJ mol À1 for Na and Cs, respectively. The calculated dopant solubility increases in the order Na < Cs < Rb < K, with the predicted solubilities of the two latter being in the range of that of e.g. Y. Although Cs would lead to the highest proton mobility, the higher solubility of K and Rb renders them more attractive A-site dopants for BaZrO 3 . Overall, our results suggest that alkali metals as A-site dopants may enhance the bulk proton conductivity of BaZrO 3 , compared to Y-doped BaZrO 3 .

Thermal and Chemical Expansion in Proton Ceramic Electrolytes and Compatible Electrodes

“…For most proton conducting oxides, β hydr has been determined in the region of 0.05-0.2 [75,[77][78][79][80][81][82][83][84][85][86]. This corresponds to a volume increase of +0.25-1.0% upon hydration for a proton concentration of 10 mol%.…”

“…Such defect associations will only affect the chemical expansion upon hydration if β (Acc OH O ) × and/or β (Acc v O ) • differ significantly from the corresponding chemical expansion coefficients for the isolated proton and oxygen vacancy, β OH • O and β v •• O , respectively. Although there is little data available specifically addressing the effects of different dopants on β hydr , there appears to be a general tendency for the chemical expansion coefficient upon hydration to increase with increasing dopant size [83,85]. Furthermore, such defect associations may also impose a temperature dependence on β hydr , as experiments may be conducted under conditions where the oxygen vacancies and/or protons are partially associated to the acceptors.…”

“…Interestingly, this is in good correspondence with work by Kreuer [80], who showed that the chemical expansion of BaZr 0.8075 Ce 0.0425 Y 0.15 O 3−δ is significantly smaller than that of BaZr 0. 85 higher temperatures will thus be a combination of several defect equilibria. This change in hydration mechanisms could therefore be the reason for the change in hydr as the proton concentration increases.…”

Corrosion Behaviour of Selective Laser Melted Ti-TiB Biocomposite in Simulated Body Fluid

“…Commercially pure titanium (CP-Ti) has been routinely employed in the area of biomedical treatment over the last 40 years or so [1][2][3]. This revolutionary application was triggered due to the perceived biocompatibility and appropriate mechanical properties of CP-Ti [4][5][6], which does not cause allergy and produce human pollutants when it is used as artificial scaffold, hip joint and dental implants [7][8][9].…”

First‐principles investigation of chemical stability and proton conductivity of M‐doped BaZrO3 (M=K, Rb, and Cs)

“…studied Y‐doping at the A site of BaZrO 3 and found that this doping improved the proton conductivity in strained system from their DFT calculations . Løken et al., in particular, calculated hydration enthalpies of the Na‐, K‐, Rb‐, or Cs‐doped BaZrO 3 and found that hydration enthalpies became more negative with decreases in the ionic radii of dopants . Using molecular dynamics (MD) simulations of Y‐ or Zn‐doped BaZrO 3 , Kitamura et al.…”