Oxygen Migration Pathways in Layered LnBaCo2O6-δ (Ln = La – Y) Perovskites

Layered LnBaCo2O6-δ perovskites are important mixed ionic-electronic conductors, exhibiting outstanding catalytic properties for the oxygen evolution/reduction reaction. These phases exhibit considerable structural complexity, in particular, near room temperature, where a number of oxygen vacancy ordered superstructures are found. This study uses bond valence site energy calculations to demonstrate the key underlying structural features that favor facile ionic migration. BVSE calculations show that the 1D vacancy ordering for Ln = Sm–Tb could be beneficial at low temperatures as new pathways with reduced barriers emerge. By contrast, the 2D vacancy ordering for Ln = Dy and Y is not beneficial for ionic transport with the basic layered parent material having lower migration barriers. Overall, the key criterion for low migration barriers is an expanded ab plane, supported by Ba, coupled to a small Ln size. Hence, Ln = Y should be the best composition, but this is stymied by the low temperature 2D vacancy ordering and moderate temperature stability. The evolution of the oxygen cycling capability of these materials is also reported.


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Table S8.Linear fit parameters used to fit the volume expansion of YBaCo 2 O 6-δ between RT -200 °C and 500 -800 °C.These fits were used to determine the thermal expansion coefficient (α) due to regular thermal expansion (i.e. in the absence of chemical reduction).The temperature dependence of the reduced volume is shown in Fig. S6.

Fig. S1 . 8 Fig. S2 .
Fig. S1.Rietveld fits to X-ray powder diffraction data for LnBaCo 2 O 6-δ (Ln = La, Pr, Nd, Sm).Data are shown open blue circles, the fit is the solid black line, and the difference curves are shown as green lines.Bragg peak positions are indicated by vertical markers.Oxygen coordinates were kept at their pseudo-cubic positions.

Fig. S5 .
Fig. S5.Temperature evolution of impurity phase weight fractions for the YBaCo 2 O 6-δ sample between RT and 800 °C upon heating and after cooling to 300 C (open symbol) under N 2 flow.

Table S5 .
Atomic coordinates for YBaCo 2 O 6-δ between 350 and 800 °C upon heating and at 300 °C after cooling.

Table S6 .
Impurity weight fractions for YBaCo 2 O 6-δ between room temperature and 800 °C upon heating and at 300 C after cooling.

Table S7 .
Bond valence sums for YBaCo 2 O 6-δ between RT and 800 °C upon heating and at 300 °C after cooling.