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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.

No MeSH data available.


Schematic presentations of the energy diagrams for the Co3+ ion in the idealized A site with the D4h symmetry and in the idealized B site with the Oh symmetry in (Sc0.95Co0.05)CoO3 (where α0 and α4 are radial integrals, JH is the intra-atomic Hund energy).
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Figure 6: Schematic presentations of the energy diagrams for the Co3+ ion in the idealized A site with the D4h symmetry and in the idealized B site with the Oh symmetry in (Sc0.95Co0.05)CoO3 (where α0 and α4 are radial integrals, JH is the intra-atomic Hund energy).

Mentions: The presence of Co3+ ions in the LS and HS states is in qualitative agreement with the energy diagrams of Co3+ in crystal fields with local symmetries of Oh (for the B position, in the first approximation) and D4h (for the A position, in the first approximation) (figure 6) [30]. In the case of the same average bond distances 〈Co-O〉, the crystal field splitting, 5/3α4 (where α4 ∼ 1/[〈Co-O〉]5 is a radial integral), of Co3+ orbitals for the Oh octahedral site is higher than the crystal field splitting for the D4h site (16/27α′4). Moreover, the average 〈Co-O〉 bond distances are longer in the A position in comparison with the B position (table 2), thus, further reducing the 16/27α′4 value and the crystal field splitting. In the case of the Oh octahedral site, where the LS state of Co3+ is experimentally realized, it gives α4 > 6/5JH, where JH is the intraatomic Hund energy, [ELS–EHS = (6×(−2/3α4) + 2 × (−3JH))–(1×(−2/3α4) + (−10JH)) < 0]. In the case of the D4h site, the LS state of Co3+ will only be realized at α′4 > 27/10JH, [ELS–EHS = (2×(−8/9α′4) + 4×(−4/27α′4) + 2×(−3JH)) –(1×() + (−10JH)) < 0]. Considering that α′4 should be smaller than α4 (and with the same JH for Co3+), the above conditions result in the HS state of Co3+ at the D4h site. Note that the HS state of Co3+ was experimentally found in BiCoO3 [31], where Co3+ ions are located in a square pyramidal coordination.


Structure and cation distribution in perovskites with small cations at the A site: the case of ScCoO 3
Schematic presentations of the energy diagrams for the Co3+ ion in the idealized A site with the D4h symmetry and in the idealized B site with the Oh symmetry in (Sc0.95Co0.05)CoO3 (where α0 and α4 are radial integrals, JH is the intra-atomic Hund energy).
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Related In: Results  -  Collection

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Figure 6: Schematic presentations of the energy diagrams for the Co3+ ion in the idealized A site with the D4h symmetry and in the idealized B site with the Oh symmetry in (Sc0.95Co0.05)CoO3 (where α0 and α4 are radial integrals, JH is the intra-atomic Hund energy).
Mentions: The presence of Co3+ ions in the LS and HS states is in qualitative agreement with the energy diagrams of Co3+ in crystal fields with local symmetries of Oh (for the B position, in the first approximation) and D4h (for the A position, in the first approximation) (figure 6) [30]. In the case of the same average bond distances 〈Co-O〉, the crystal field splitting, 5/3α4 (where α4 ∼ 1/[〈Co-O〉]5 is a radial integral), of Co3+ orbitals for the Oh octahedral site is higher than the crystal field splitting for the D4h site (16/27α′4). Moreover, the average 〈Co-O〉 bond distances are longer in the A position in comparison with the B position (table 2), thus, further reducing the 16/27α′4 value and the crystal field splitting. In the case of the Oh octahedral site, where the LS state of Co3+ is experimentally realized, it gives α4 > 6/5JH, where JH is the intraatomic Hund energy, [ELS–EHS = (6×(−2/3α4) + 2 × (−3JH))–(1×(−2/3α4) + (−10JH)) < 0]. In the case of the D4h site, the LS state of Co3+ will only be realized at α′4 > 27/10JH, [ELS–EHS = (2×(−8/9α′4) + 4×(−4/27α′4) + 2×(−3JH)) –(1×() + (−10JH)) < 0]. Considering that α′4 should be smaller than α4 (and with the same JH for Co3+), the above conditions result in the HS state of Co3+ at the D4h site. Note that the HS state of Co3+ was experimentally found in BiCoO3 [31], where Co3+ ions are located in a square pyramidal coordination.

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.