Synthesis, structure and magnetic properties of new γ-Ba(CoV1-xPxO4)2 x=0.4-0.5

The phase composition of the system BaCo2(VO4)(2)-Ba(CoPO4)(2) has been studied. At room temperature two miscibility gaps have been detected, with the formation of substitutional solid solutions Ba(CoV1-xPxO4)(2) for x = 0.4-0.5 basing on the gamma-BCPO structure type. An increase in the vanadium cation concentration leads to the stabilization of the rhombohedral crystal lattice. The crystallographic characteristics of two new phosphate - vanadates Ba(CoV0.5P0.5O4)(2) and Ba(CoV0.6P0.4O4)(2) isostructural to gamma-BCPO have been obtained, their crystal structures have been described, and their magnetic properties have been analyzed. It was shown that in alpha-BCPO, as distinct from other examined phases, a three-dimensional ferromagnetic ordering characterized by a wide hysteresis loop takes place at low temperatures. The enhanced values of the magnetic moment in the paramagnetic phase BaCo2(VO4)(2) and solid solutions based on gamma-BCPO are attributed to the peculiarities of the crystal environment.