New Route of Preparation and Properties of NaNiO 2

NaNiO 2 was prepared through oxidation of a Na 2 NiO 2 / NiO mixture (1:1) in dried oxygen at 500 °C. Single crystals have been grown by annealing of NaNiO2 powder at 600 °C for 83 d in a flow of dried oxygen. According to the X-ray analysis of the crystal structure (C2/m, Z = 2, a = 5.3177(2), b = 2.8458(1), c = 5.5819(3) Å , β = 110.409(2)°, R 1 (all) = 3.4%, 185 independent reflections), the Jahn-Teller distorted NiO 6 octahedra, sharing edges, build up layers lying parallel to the ab plane. A phase transition (associated with an energy of 2.9 kJ/mole) to a high temperature rhombohedral form (R3̅m, Z = 3, a = 2.958(1), c = 15.748(2) Å , at 300 °C) was observed by Guinier and DSC measurements at 195 °C. The magnetic susceptibility of the monoclinic phase can be described by the Curie-Weiss law between 100 and 330 K: μ = 2.01μB (g = 2.32), Θ = 37 K, indicating the dominance of ferromagnetic interactions of S = 1 / 2 spins within the NiO 2 layers. Antiferromagnetic interlayer interactions produce an overall antiferromagnetically ordered structure below 18 K.