Determination of the modulated structure of Sr_14/11CoO₃ through a (3 + 1)-dimensional space description and using non-harmonic ADPs

Abstract

Sr(14/11)CoO(3) (i.e. Sr(14)Co(11)O(33), tetradecastrontium undecacobalt tritriacontaoxide), a new phase in the hexagonal perovskite Sr(x)CoO(3) system, has been prepared and its structure solved from single-crystal X-ray data within the (3 + 1)-dimensional formalism. Sr(14/11)CoO(3) crystallizes in the trigonal symmetry, R3;m(00gamma)0s superspace group with the following lattice parameters: a(s) = 9.508 (2), c(s) = 2.5343 (7) Å, q = 0.63646 (11)c(*) and V(s) = 198.40 (13) Å(3). With the commensurate versus incommensurate test not being conclusive, the structure was considered as commensurate (P32 three-dimensional space group), but refined within the (3 + 1)-dimensional formalism to a residual factor R = 0.0351 for 47 parameters and 1169 independent reflections. Crenel functions were used for the oxygen and cobalt description and a Gram-Charlier expansion up to the third order of the atomic displacement parameter was employed for one Co atom. The structure is similar to that of Sr(6/5)CoO(3), but with a different sequence of the octahedra and trigonal prism polyhedra along the [CoO(3)] chains. An interesting feature evidenced by the non-harmonic expansion is the displacement of the prismatic Co atoms from the site center, towards the prism rectangular faces.

Structural studies of a mixed-valence state in the incommensurate composite crystal Sr1.261CoO3

“…In particular, the charge balance in the Oh and TP sites should be considered in connection with the magnetic state in Sr 2γ CoO 3 . Gourdon et al expected that Sr 14/11 CoO 3 possesses the oxidation state of the separate Co ions: with the Co 2+ in TP sites and Co 4+ in Oh sites [9]. This charge balance, i.e.…”

“…However, it is inappropriate to describe all the structures within the hexagonal perovskite system. For instance, Sr 14 Co 11 O 33 [9] would require a fractional number of m = 5/3 if this formula is applied to the compound. In addition, the 3D formalism is not applicable to incommensurate structure compounds such as Sr 1.2872 NiO 3 [10], Sr 1+x (Co x Mn 1−x )O 3 [11], [Ba] x [(Pt, Cu)O 3 ] [12], or Sr 1.145 TiS 3 [13].…”

Influence of Phase Transformations on Crystal Growth of Stoichiometric Brownmillerite Oxides: Sr2ScGaO5 and Ca2Fe2O5

“…Adjusting the appropriate oxygen stoichiometry corresponding to the ideal A 2 B 2 O 5 composition requires a perfect knowledge of the phase diagram; i.e., the oxygen stoichiometry at high temperatures as a function of the applied p(O 2 ). However, while SrFeO 2.5 can then be obtained by furnace cooling under controlled p(O 2 ), this is no longer true for SrCoO 2.5 under similar reaction conditions, as slow cooling results in a phase segregation and the formation of a Co-deficient modulated hexagonal modification Sr x CoO 3 (x = 14/11) [7]. Stoichiometric SrCoO 2.5 can only be obtained by quenching from high temperatures, and is consequently a metastable phase at room temperature.…”

“…In the last decades, brownmillerite type oxides have received considerable attention, because of their rich chemistry, structural complexity, and for their interesting properties and applications [1][2][3][4][5][6][7][8]. With the general formula A 2 BB O 5 , the brownmillerite framework can be described as an oxygen-anion-deficient perovskite phase, and its structure can be derived from the cubic phase by releasing 1/6 of all oxygen atoms in an ordered way along the [110] direction of the cubic perovskite.…”

Structure Determination of Ba8CoRh6O21, a New Member of the 2H-Perovskite Related Oxides

“…As shown previously, a better structural formulation of such composites is A 1+x (A' x B 1-x )O 3 , where x = n/(3m+2n) and ranges continuously between 0 and 1/2, corresponding to chains containing all face-shared octahedra and alternating face-sharing octahedra and trigonal prisms, respectively. [27][28][29] For simple fractional values of x such as 1/5, 2/7, or 1/3, the structure is commensurate and the endmembers, the 2H perovskite (BaNiO 3 , x = 0) and the K 4 CdCl 6 (x = 1/2) structure type, are well known.…”