Continuous structural phase transition and antiferromagnetic order in ilmenite-type NiVO3

We investigate the crystal and electronic structures as well as magnetic properties of ilmenite-type NiVO3, which has attracted research interest as an S = 1 honeycomb lattice magnet. Ilmenite-type NiVO3 samples were synthesized under high-pressure and high-temperature conditions. Synchrotron x-ray diffraction and Rietveld refinement results demonstrated that NiVO3 underwent a continuous structural phase transition from the triclinic (P1¯) phase to the rhombohedral (R3¯) phase at 450 K. This transition is concomitant with the decomposition of the V-V dimers formed by the tetravalent V ions. X-ray absorption spectroscopy measurements confirmed that the Ni and V ions were divalent and tetravalent, respectively. Magnetic and specific heat measurements revealed that NiVO3 underwent an antiferromagnetic transition at 140 K, and a zigzag-type magnetic order with magnetic propagation vector k=(0,1/2,0) was observed by neutron diffraction measurements.