Oxygen over stoichiometry in the 2H-perovskite related structure: the route to a large family of cation deficient Ising chain oxides Sr1+y[(Mn1−xCox)1−z□z]O3†
The realization of oxygen over stoichiometry through oxidation of Co2+ into Co3+ in the 2H-perovskite related oxides Sr1+x(Mn1−xCox)O3 is demonstrated, leading to a large family of cation deficient Ising chain oxides Sr1+y[(Mn1−xCox)1−z□z]O3. In these aperiodic hexagonal structures, also formulated as Sr1+x(Mn1−xCox)O3+δ (a ≈ 9.6 Å, c1 ≈ 2.6 Å, c2 ≈ 3.9 Å), and built up of face sharing octahedra and trigonal prismatic polyhedra, the observed modulation vector γ = c1/c2 (ranging from ∼0.641 to ∼0.668) allows the proportion of octahedral (NO) and prismatic sites (NP) to be obtained according to the relationships: y = 2γ − 1 = NP/(NP + NO). For these oxides, the content of cationic vacancies (z) in the chains and the oxygen over-stoichiometry (δ) can be deduced from the relationships: z = (x − y)/(1 + x) and δ = 3(x − y)/(1 + y). The analysis of these results shows that the structure of the chains, i.e., the proportion of tetrameric units “M4O12” coexisting with trimeric units “M3O9”, is highly sensitive to the oxygen over-stoichiometry for a fixed cationic composition. This is illustrated here by the structure of the oxide corresponding to x = 0.375 with δ = 0.09, which is commensurate with γ = 2/3, similar to Sr4Mn2CoO9, but with a significant content of cationic vacancies in the trigonal prismatic sites according to the formula Sr4(MnIV1.818CoIII0.544 CoII0.548□0.09)O9. Thus, the presence in those chains of cationic vacancies due to oxygen overstoichiometry appears as a very important concept which opens the route to the synthesis of fragmented chain structures and may have a huge impact upon the magnetic and magneto-electric behavior of Ising chain oxides.