Evidence for nickel-(I)-rich mixed oxide with a defect K2NiF4-type structure

High‐Temperature Structural and Electrical Characterization of Reduced Oxygen‐Deficient Ruddlesden–Popper Nickelates

“…The structural model implies also that Ni cations randomly adopt three different coordination states in the lattice (Figure B): octahedral (CN = 6), pyramidal (CN = 5), and square‐planar (CN = 4). The crystal structure is closely related to that reported for La‐rich (La 1– x Sr x ) 2 NiO 4– δ nickelates heavily reduced in controlled H 2 ‐containing atmosphere and containing nickel in mixed 1+/2+ oxidation state . This type of structure is also characteristic of orthorhombic Sr 2 CuO 3 ,, which adopts the same Immm space group, but with fully vacant oxygen 2 d Wyckoff positions and all copper ions in square‐planar coordination resulting in isolated Cu–O chains (Figure C).…”

Factors Influencing the Stabilization of Ni+ in Perovskite-Related Oxides

“…X-ray di!raction analysis of the products obtained after heating the La \V Sr V NiO samples to point A in the TGA and cooling to room temperature indicates them to have the Sr CuO structure, and the lattice parameters are given in Table 1 and plotted in Fig. 5 (20,21) employed a specially designed closed gas system in which the degree of reduction could be monitored by following the volume of hydrogen consumed. The di!erences in the oxidation state of Ni in the products obtained by dynamic and static reduction procedures reveal that the extent of stabilization of Ni> is sensitive to the synthesis conditions.…”

“…The "rst e!ort in this direction was by Crespin et al (18,19) to obtain the in"nite-layer compound LaNiO by a controlled hydrogen reduction of the perovskite oxide LaNiO . Following this, Crespin et al (20,21) La \V Nd V Ni O (n"3 member) are investigated. The results demonstrate the importance of bond length matching between the adjacent layers as well as the coordination preferences of¸n> ions in stabilizing Ni>.…”

Synthesis and characterization of La1+Sr2−CoMnO7− (x=0,0.2; δ=0,1)

“…In the n ¼1 RP phases, the oxide ion vacancies preferentially distribute within the MO 2 planes of the perovskite layers where the vacancies may be ordered [6,7,12] or disordered [8,9,13]. A disordered distribution of vacancies within the equatorial MO 2 planes has also been reported for the n ¼2 RP Sr 3 Mn 2 O 6.55 [14].…”

“…Oxygen deficiency can also be induced by controlled reduction of near-stoichiometric phases in hydrogen. Examples include many n ¼1 RP phases such as La 2 À x Sr x NiO 4 À d; [6,7] and La 2 À x Sr x Co 0.5 Fe 0.5 O 4 À d; [8,9]. Powerful reducing agents such as calcium hydride have recently been used to produce highly oxygen-deficient phases in which unusual two-dimensional coordination geometries of transition metal ions such as cobalt and iron have been achieved [10,11].…”