Maximizing proton conductivity is a necessity in the
design of
efficient oxide proton-conductive membranes for electrochemical applications.
Acceptor doping makes it possible to achieve a high concentration
of charge carriers but encounters problems of phase stability or defect
interaction. Sr is the optimal dopant for perovskite-like lanthanum
scandate. La1–x
Sr
x
ScO3−δ (0.05 ≤ x ≤ 0.20) solid solutions demonstrate phase and structural
stability and high levels of hydration. Compositions with x = 0.1 and 0.15 reach proton conductivity of 5 mS/cm at
600 °C and air humidity 2.8 kPa; however, for compositions x ≥ 0.15, an increase in temperature above 500 °C
causes a drastic loss of protons. It is probably associated with the
clustering of oxygen vacancies, which is confirmed by an anomalous
increase in the thermodynamic parameters of hydration, chemical expansion
values, and activation energies of proton and oxide-ion transfer.
Thus, both high proton transfer activation energies and chemical expansion
values for compositions x ≥ 0.15 can become
a challenge in the production and operation of electrolytic membranes,
whereas compositions x ∼ 0.1 are most preferred.