Unusual Coexistence of Nickel(II) and Nickel(IV) in the Quadruple Perovskite Ba₄Ni₂Ir₂O₁₂ Containing Ir₂NiO₁₂ Mixed-Metal-Cation Trimers

Abstract

The crystal chemistry and magnetic properties of two hexagonal nickel(IV)-containing perovskites, BaNiIrO and BaNiO, are reported. The 12R perovskite, BaNiIrO, possesses an unexpected coexistence of nickel(II) and nickel(IV). This quadruple perovskite structure contains IrNiO mixed-metal-cation units in which direct metal-metal bonding between nickel(IV) and iridium(V) is inferred. X-ray absorption near-edge spectroscopy and X-ray photoelectron spectroscopy measurements were conducted to confirm the simultaneous presence of nickel(II) and nickel(IV).

Trimer-based spin liquid candidate Ba4NbIr3O12

“…The effective moment of Ba4NbIr3O12 is smaller than the one observed in Ba4Ni1.94Ir2.06O12, which has a mixed trimer between Ir and Ni. (17) Similar characterization of Ba4NbRh3O12 gives 𝜒 𝑜 = 2.1x10 -4 emu Oe -1 mol-f.u. -1 , 𝜇 𝑒𝑓𝑓 = 1.48 μB/f.u, and 𝛳 𝐶𝑊 = -23 K, as illustrated in Figure 3b.…”

Hexagonal Perovskite Ba4Fe3NiO12 Containing Tetravalent Fe and Ni Ions

“…This small-sized octahedron increases the crystal-field splitting energy between the t 2 g and e g orbitals of Ni and stabilizes the low-spin 3d 6 electron configuration. Actually, the S = 0 low-spin state Ni 4+ in the face-sharing octahedra was recently reported in a similar 12R hexagonal perovskite Ba 4 Ni 2 ­Ir 2 O 12 . Therefore, the observed weak ferromagnetism seems to originate from antiferromagnetic (ferrimagnetic) coupling between Fe 3+ and Fe 4+ spins, and Ni 4+ with a low-spin electron configuration does not seem to contribute to the magnetism in BFNO75.…”

Hexagonal Perovskites as Quantum Materials

“…The crystal structure consists of facesharing Ir2NiO12 trimers and layers of single NiO6 octahedra. This material is claimed to have the unusual mix of Ni 2+ and Ni 4+ in its structure, according to XANES measurements 142 (Figure 15b). Fitting of the magnetic susceptibility data yields a Curie-Weiss temperature of -33 K and the effective moment of 4.40 µB/f.u, with data as shown in Figure 15c.…”