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Structure and cation distribution in perovskites with small cations at the A site: the case of ScCoO 3

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ABSTRACT

We synthesize ScCoO3 perovskite and its solid solutions, ScCo1−xFexO3 and ScCo1−xCrxO3, under high pressure (6 GPa) and high temperature (1570 K) conditions. We find noticeable shifts from the stoichiometric compositions, expressed as (Sc1−xMx)MO3 with x = 0.05–0.11 and M = Co, (Co, Fe) and (Co, Cr). The crystal structure of (Sc0.95Co0.05)CoO3 is refined using synchrotron x-ray powder diffraction data: space group Pnma (No. 62), Z = 4 and lattice parameters a = 5.26766(1) Å, b = 7.14027(2) Å and c = 4.92231(1) Å. (Sc0.95Co0.05)CoO3 crystallizes in the GdFeO3-type structure similar to other members of the perovskite cobaltite family, ACoO3 (A3+ = Y and Pr-Lu). There is evidence that (Sc0.95Co0.05)CoO3 has non-magnetic low-spin Co3+ ions at the B site and paramagnetic high-spin Co3+ ions at the A site. In the iron-doped samples (Sc1−xMx)MO3 with M = (Co, Fe), Fe3+ ions have a strong preference to occupy the A site of such perovskites at small doping levels.

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57Fe Mössbauer spectra at 300 K and fitting results for (a) (Sc0.95M0.05)MO3 ( and (b) (Sc0.89M0.11)MO3 (M = Co0.6Fe0.4). The difference between the experimental and calculated spectra is shown at the bottom. (c) Distribution functions p(ΔFe1) of the quadrupole splitting ΔFe1 for the Fe1 subspectrum in (Sc0.95M0.05)MO3 ( (green crosses) and (Sc0.89M0.11)MO3 (M = Co0.6Fe0.4) (red squares).
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Figure 2: 57Fe Mössbauer spectra at 300 K and fitting results for (a) (Sc0.95M0.05)MO3 ( and (b) (Sc0.89M0.11)MO3 (M = Co0.6Fe0.4). The difference between the experimental and calculated spectra is shown at the bottom. (c) Distribution functions p(ΔFe1) of the quadrupole splitting ΔFe1 for the Fe1 subspectrum in (Sc0.95M0.05)MO3 ( (green crosses) and (Sc0.89M0.11)MO3 (M = Co0.6Fe0.4) (red squares).

Mentions: The Mössbauer spectrum of (Sc0.95M0.05)MO3 ( at 300 K is shown on figure 2(a). It clearly consists of two doublets, Fe1 and Fe2, whose isomer shift (δFe1 < δFe2) and quadrupole splitting (ΔFe1 < ΔFe2) values indicate that the high-spin (HS) Fe3+ ions occupy two positions with different oxygen surrounding. The existence of these doublets could only originate from 57Fe3+ ions in positions corresponding to the A and B sublattices. The δFe1 (=0.32(1) mm s−1) and ΔFe1 (=0.42(1) mm s−1) values for the first Fe1 doublet are in good agreement with the δ = 0.31–0.33 mm s−1 and Δ = 0.38–0.50 mm s−1 values for Fe3+ ions located in the B site of Fe0.02O3 (R = Y, Eu and Lu) perovskites [22]. Taking into account that an increase in the average 〈Fe-O〉 distances leads generally to an increase in δ values [23], the Fe2 doublet with the larger isomer shift of δFe2 = 0.45(1) mm s−1 should correspond to 57Fe3+ ions located at the larger A site, and the larger quadrupole splitting of ΔFe2 = 1.26(1) mm s−1 indicates that Fe3+ ions have highly asymmetric coordination at the A site. It is expected that smaller 3d transition metals (Cr3+, Fe3+ and Co3+) should be displaced off the position occupied by the larger Sc3+ ions similar to the displacement of Mn2+ ions found in Sr0.98Mn0.02TiO3 [10]. Based on experimental values of the areas of the two doublets (IFe values in table 3), the distribution of 57Fe3+ ions is not statistical (the statistical distribution would result in about 5% of 57Fe3+ ions at the A site), but 57Fe3+ ions preferably occupy the A site (about 30%).


Structure and cation distribution in perovskites with small cations at the A site: the case of ScCoO 3
57Fe Mössbauer spectra at 300 K and fitting results for (a) (Sc0.95M0.05)MO3 ( and (b) (Sc0.89M0.11)MO3 (M = Co0.6Fe0.4). The difference between the experimental and calculated spectra is shown at the bottom. (c) Distribution functions p(ΔFe1) of the quadrupole splitting ΔFe1 for the Fe1 subspectrum in (Sc0.95M0.05)MO3 ( (green crosses) and (Sc0.89M0.11)MO3 (M = Co0.6Fe0.4) (red squares).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5036463&req=5

Figure 2: 57Fe Mössbauer spectra at 300 K and fitting results for (a) (Sc0.95M0.05)MO3 ( and (b) (Sc0.89M0.11)MO3 (M = Co0.6Fe0.4). The difference between the experimental and calculated spectra is shown at the bottom. (c) Distribution functions p(ΔFe1) of the quadrupole splitting ΔFe1 for the Fe1 subspectrum in (Sc0.95M0.05)MO3 ( (green crosses) and (Sc0.89M0.11)MO3 (M = Co0.6Fe0.4) (red squares).
Mentions: The Mössbauer spectrum of (Sc0.95M0.05)MO3 ( at 300 K is shown on figure 2(a). It clearly consists of two doublets, Fe1 and Fe2, whose isomer shift (δFe1 < δFe2) and quadrupole splitting (ΔFe1 < ΔFe2) values indicate that the high-spin (HS) Fe3+ ions occupy two positions with different oxygen surrounding. The existence of these doublets could only originate from 57Fe3+ ions in positions corresponding to the A and B sublattices. The δFe1 (=0.32(1) mm s−1) and ΔFe1 (=0.42(1) mm s−1) values for the first Fe1 doublet are in good agreement with the δ = 0.31–0.33 mm s−1 and Δ = 0.38–0.50 mm s−1 values for Fe3+ ions located in the B site of Fe0.02O3 (R = Y, Eu and Lu) perovskites [22]. Taking into account that an increase in the average 〈Fe-O〉 distances leads generally to an increase in δ values [23], the Fe2 doublet with the larger isomer shift of δFe2 = 0.45(1) mm s−1 should correspond to 57Fe3+ ions located at the larger A site, and the larger quadrupole splitting of ΔFe2 = 1.26(1) mm s−1 indicates that Fe3+ ions have highly asymmetric coordination at the A site. It is expected that smaller 3d transition metals (Cr3+, Fe3+ and Co3+) should be displaced off the position occupied by the larger Sc3+ ions similar to the displacement of Mn2+ ions found in Sr0.98Mn0.02TiO3 [10]. Based on experimental values of the areas of the two doublets (IFe values in table 3), the distribution of 57Fe3+ ions is not statistical (the statistical distribution would result in about 5% of 57Fe3+ ions at the A site), but 57Fe3+ ions preferably occupy the A site (about 30%).

View Article: PubMed Central - PubMed

ABSTRACT

We synthesize ScCoO3 perovskite and its solid solutions, ScCo1&minus;xFexO3 and ScCo1&minus;xCrxO3, under high pressure (6 GPa) and high temperature (1570 K) conditions. We find noticeable shifts from the stoichiometric compositions, expressed as (Sc1&minus;xMx)MO3 with x = 0.05&ndash;0.11 and M = Co, (Co, Fe) and (Co, Cr). The crystal structure of (Sc0.95Co0.05)CoO3 is refined using synchrotron x-ray powder diffraction data: space group Pnma (No. 62), Z = 4 and lattice parameters a = 5.26766(1) &Aring;, b = 7.14027(2) &Aring; and c = 4.92231(1) &Aring;. (Sc0.95Co0.05)CoO3 crystallizes in the GdFeO3-type structure similar to other members of the perovskite cobaltite family, ACoO3 (A3+ = Y and Pr-Lu). There is evidence that (Sc0.95Co0.05)CoO3 has non-magnetic low-spin Co3+ ions at the B site and paramagnetic high-spin Co3+ ions at the A site. In the iron-doped samples (Sc1&minus;xMx)MO3 with M = (Co, Fe), Fe3+ ions have a strong preference to occupy the A site of such perovskites at small doping levels.

No MeSH data available.


Related in: MedlinePlus