CaMn_0.5Ir_0.5O_2.5: An Anion-Deficient Perovskite Oxide Containing Ir³

Reaction between CaMn_0.5Ir_0.5O₃ and NaH, either through solid-solid contact or via a gas mediated reaction process, yields the topochemically reduced phase CaMn_0.5Ir_0.5O_2.5 in which Mn³⁺ and Ir³⁺ cations are located within a partially anion-vacancy disordered lattice. Magnetization data from CaMn_0.5Ir_0.5O_2.5 can be fit by the Curie-Weiss law to yield C = 1.586 cm³ K mol^-1 and θ = -86.9 K, consistent with a combination of S = 2, Mn³⁺ and S = 0, Ir³⁺. On cooling below T ∼ 110 K, the system undergoes a transition to a spin-glass state, consistent with the observed Mn/Ir cation disorder and frustration between Mn-O-Mn and Mn-O-Ir-O-Mn magnetic couplings. The degree of reduction and the observed anion-vacancy disorder are discussed on the basis of the d-orbital filling of the transition-metal cations.