Control of Magnetism via B-Site Order and Disorder in Y₂NiTiO₆ Perovskite

The first reported phase in the Y₂O₃-NiO-TiO₂ chemical space, the Y₂NiTiO₆ perovskite undergoes a temperature-induced order-disorder transition. Above ∼1700 K, it adopts the structure of a disordered CaTiO₃-type orthorhombic perovskite with a = 5.26939(2), b = 5.60367(2), and c = 7.58137(3) Å, with the B site uniformly occupied by 0.5Ni+0.5Ti. Below this temperature, Y₂NiTiO₆ adopts rock-salt ordering of the transition metals in a monoclinic unit cell (a = 5.26695(2), b = 5.60164(2), c = 7.57493(2) Å, β = 90.4940(2)°) with 0.9/0.1 ordering of the B site. Ordering of Ni and Ti changes the magnetic properties from spin-glass behavior in the orthorhombic phase to antiferromagnetic order (T_N = 17 K) for the monoclinic phase, while the optical properties of both phases remain unchanged across the transition.