Structure and magnetic properties of Ni4V3O10, an antiferromagnet with three types of vanadium-oxygen polyhedra

The compound Ni4V3O10 forms a new structure type in the tetragonal space group P4/n. The material can be produced using solid-state synthesis in a narrow temperature range, and the structure was confirmed using X-ray and neutron powder diffraction data. The phase contains occupationally disordered Ni/V in tetrahedral, square pyramidal, and octahedral sites. Bond valence and neutron/X-ray co-refinements give evidence for three vanadium oxidation states (V^3+, V^4+, V^5+), making it distinct in the Ni-V-O system and placing it in a class of only nine other oxides with transition metals exhibiting three oxidation states. With a Néel temperature of 38 K and a Curie-Weiss parameter θ = -234 K, it displays frustrated antiferromagnetism, evidenced by a broad hump in the heat capacity below T_N. The structure has a percolating distorted rock-salt-like network, leading to strong superexchange, but square pyramidal linkages frustrate magnetic ordering. The magnetic structure is assumed to be incommensurate, as simple propagation vectors can be ruled out by powder neutron diffraction.