Indium doping in SrCeO3 proton-conducting perovskites

In this work we present results of studies of In3+ doping in strontium cerate, comprising structural aspects, and oxygen as well as proton conductivity. Crystal structure analysis of single-phase SrCe1-xInxO3-a (x ​= ​0.1, 0.2 and 0.3) materials in 25–900 ​°C temperature range indicates presence of strong orthorhombic distortion of the perovskite-type structure, similar as for the undoped SrCeO3. Limited sinterability of the obtained powders was mitigated by addition of 1 ​wt% of NiO, which allowed to manufacture dense sinters at 1400 ​°C. Electrochemical impedance spectroscopy measurements done in dry synthetic air show decrease of the ionic (oxygen) conductivity with the increase of In content, as well as associated increase of the activation energy. This indicates that formed oxygen vacancies are trapped in the structure. Overall, electrical conductivity for SrCe1-xInxO3-a in H2O- and D2O-containing atmospheres decreases with In content, but respective H+ and D+ transference numbers are larger for samples with higher indium doping. At 500 ​°C the highest proton and deuterium conductivity was recorded for SrCe0.9In0.1O3-a, reaching up to 0.70·10−4 ​S ​cm−1 and 0.26·10−4 ​S ​cm−1, respectively. Derived diffusion and surface exchange coefficients are 10−7-10−6 ​cm2 ​s−1 and 10−6-10−5 ​cm ​s−1, respectively in 500–700 ​°C temperature range.