Structure and cation distribution in perovskites with small cations at the A site: the case of ScCoO₃

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.

Perovskite-Type InCoO3 with Low-Spin Co3+: Effect of In–O Covalency on Structural Stabilization in Comparison with Rare-Earth Series

“…For each of the data sets, the main reflections can be indexed in orthorhombic symmetry with a √2ap × 2ap ×√2ap unit cell (where ap is the lattice parameter of basic cubic perovskite). In contrast to the case of (Sc0.95Co0.05)CoO3 prepared at 6 GPa and 1297 °C, 17 no reflections from bixbyite-type Sc2O3 are found in the SXRD pattern for ScCoO3. Instead, a few weak reflections from unknown phases are observed; the intensities of impurity reflections were less than 0.8 % of the intensities of the most intense perovskite reflections ( Figure S1 in the Supporting Information,).…”

“…25,[32][33][34] In (a), the experimental lattice parameters for (Sc0.95Co0.05)CoO3 (black) are displayed for comparison. 17 In (b), the calculated lattice parameters for TlCoO3 (green) are shown as a reference. Insets depict the rA-dependent variations in (a) experimental and (b) calculated orthorhombic strain, s = 2(a c)/(a + c).…”

“…Figure 4 (a) Variations in unit-cell volume with A 3+ ionic radius, rA (in 8-fold coordination 60 ) for ScCoO3 (red), InCoO3 (blue), and ACoO3 where A = Y and Pr-Lu (black). 25,[32][33][34] The unit-cell volume for (Sc0.95Co0.05)CoO3 (black) 17 is also displayed for comparison. 17 (b) Variation in octahedral tilt angles with A 3+ ionic radius, rA (in 8-fold coordination 60 ) for ScCoO3 (red), InCoO3 (blue), and ACoO3 where A = Y, Pr, Nd, and Tb-Lu (black).…”

“…25,[32][33][34] The unit-cell volume for (Sc0.95Co0.05)CoO3 (black) 17 is also displayed for comparison. 17 (b) Variation in octahedral tilt angles with A 3+ ionic radius, rA (in 8-fold coordination 60 ) for ScCoO3 (red), InCoO3 (blue), and ACoO3 where A = Y, Pr, Nd, and Tb-Lu (black). 25,[32][33][34] The inphase (a 0 b + a 0 ) and out-of-phase (ab 0 a -) tilt angles as well as the average tilt angle were calculated from the oxygen fractional coordinates by the equations given in ref.…”

“…With increasing temperature, they undergo two magnetic transitions associated with thermal excitations to either the intermediate-spin (t2g 5 eg 1 , S = 1) or high-spin (t2g 4 eg 2 , S = 2); although the nature of paramagnetic Co 3+ species is still under debate, the first magnetic transition is ascribed to the diamagnetic-paramagnetic transition, [26][27][28][29] and the second one to the transition to another paramagnetic state accompanied by an insulator-metal transition. [30][31][32][33][34] Given the fact that (Sc0.95Co0.05)CoO3 exhibits a large paramagnetic response from the high-spin Co 3+ ions on the A-site, 17 the magnetic ground states of almost stoichiometric ScCoO3 and InCoO3 deserve to be investigated to confirm a link with the wellknown members of the perovskite cobaltite series.…”