CRYSTAL-STRUCTURE AND MAGNETIC-PROPERTIES OF BA2NI(PO4)2

The structure of Ba2Ni(PO4)2 was solved by single crystal X-ray diffraction. It crystallizes in the monoclinic system with the space group P2(1)/n. The cell parameters are a = 5.312(1) angstrom, b = 8.789(2) angstrom, c = 16.067(3) angstrom and beta = 90.72(1)-degrees, Z = 4. The structure has been refined from 2979 independent reflections to R = 0.031 (Rw = 0.039). The three dimensional framework could be described from comer and edge-sharing NiO6 octahedra and PO4 tetrahedra creating two types of tunnels where are located the barium ions. Magnetic thermal susceptibility has been described in terms of antiferromagnetic isotropic interactions in dimers of Ni2+(S = 1). The best agreement between theoretical and experimental data is obtained for J = -3.93 K and g = 2. 1. The specific heat measurements suggest a second order phase transition to a magnetical 3D- order state at low temperature (T < 5.17K).