Fig. 1. XRD patterns of Sm_(1 − x)Ce_xFeO_3 ± λ sintered in air for 24 h at 850 °C. a) x = 0; b) x = 0.01; c) x = 0.03; d) x = 0.05; e) x = 0.07; f) x = 0.10. ● indicates peaks of a separate CeO₂ phase.

Fig. 2. The weighted average ionic radii of A-cation (r_A) and normalized cell volume (V^1/3) as a function of total concentration of Ce(x = x′ + x″). The solid line represents V^1/3 and broken lines show the weighted average ionic radii (r_A). The compositions corresponding to different series are: (1) Sm_1 − x′^+ 3Ce_x′^+ 3FeO₃ (x′ = 0–0.05), (2) Sm_{1 − y − x′}^+ 3Sm_y^+ 4Ce_x′^+ 3FeO₃ (x′ =0–0.05, y = 7%Sm^+ 3), (3) Sm_{1 − y − x′}^+ 3Sm_y^+ 4Ce_x′^+ 3FeO₃ (x′ = 0–0.05, y = 7%–1%Sm^+ 3), (4) Sm_{1 − y − x′ − x″}^+ 3Sm_y^+ 4Ce_x′^+ 3Ce_x″^+ 4FeO₃ (x′ + x″ = 0–0.05, x″ = 0–70%Ce^+ 3, y = 7–1%Sm^+ 3), (5) Sm_{1 − y − x′ − x″}^+ 3Sm_y^+ 4Ce_x^+ 3Ce_x″^+ 4FeO₃ (x′ + x″ = 0–0.05, x″ = 70%Ce^+ 3, y = 7%Sm^+ 3), (6) Sm_{1 − y − x′ − x″}^+ 3Sm_y^+ 4Ce_x′^+ 3Ce_x″^+ 4FeO₃ (x′ + x″ = 0–0.05, x″ = 50%Ce^+ 3, y = 7%Sm^+ 3).

Fig. 3. XRD spectra for Sm_(1 − x)Ce_xFeO_3 ± λ sintered at 900 °C in 5%H₂/N₂ for 1 h. a) x = 0; b) x = 0.01; c) x = 0.03; d) x = 0.05. indicates peaks of Sm₂O₃; + indicates Fe/Fe₂O₃.

Fig. 4. Surface morphology observed by SEM a) SmFeO₃; b) Sm_0.99Ce_0.01FeO₃ (i.e. x = 0.01).

Fig. 5. Full range XPS spectrum of (a) SmFeO₃ and (b) Sm_0.99Ce_0.01FeO_3 ± λ (x = 0.01).

Fig. 6. XPS spectrum x = 0.01 at different times showing splitting of Sm3d_5/2 and O1s peaks a and b showing Sm3d_5/2 peaks after 10.56 and 26 min respectively while c and d showing O1s peaks after 10.56 and 26 min respectively.

Fig. 7. Conductivity of Sm_(1 − x)Ce_xFeO_3 ± λ sintered at 1350 °C as a function of temperature. a and b showing electrical conductivity measured in air and 5% V/V H₂/N₂ respectively while c and d showing (σ_R − σ_O ) and σ_R/σ_O respectively as a function of temperature. Note that the solid lines joining the points are used only to guide the eye.

Fig. 8. Conductivity of Sm_(1 − x)Ce_xFeO_3 ± λ at 800–1000 °C as a function of cerium concentration. Note that the solid lines joining the points are used only to guide the eye.

Table 1.

Elemental quantification of Sm_(1 − x)Ce_xFeO_3 ± λ obtained from XRF

^a Measured by XRF using calibration curves of the corresponding oxides. Values are given as % w/w of the overall sample.
^b Oxygen cannot be measured directly. The oxygen content is calculated from the balance of the sample weight.

Table 2.

Calculated cell parameters, theoretical densities, cell volumes and crystallite sizes from XRD data of Sm_(1 − x)Ce_xFeO_3 ± λ calcined at 850 °C for 24 h

Table 3.

B.E. in (eV) and surface atomic ratio of Sm_(1 − x)Ce_xFeO_3 ± λ

^a Binding energies are calibrated by the C 1s peak, set at 284.8.eV.
^b Stoichiometric ratios are normalized to the iron content.