Crystal Structure and Magnetic Properties of BaVSi2O7

The structure of the second phase (β-) of BaVSi2O7, has been solved by single crystal X-ray diffraction, and its magnetic properties have been examined in the temperature range 5-300 K. β-BaVSi2O7 crystallizes in the tetragonal system, space group I4/m (No. 87), with a = 7.0535(7) Å, c = 11.467(2), V = 570.5(3) Å3, and Z = 4. This structure can be considered as consisting of VO6-5 square pyramids and unbranched single rings of [Si4O12]8-, or of cage-like [Si4V2O18]12- clusters formed by SiO4-4 and VO6-5 These building elements are cross-linked to form a pseudo-two-dimensional (2D) network containing empty channels perpendicular to the c-axis. The 2D networks are held together by Ba2+ ions that occupy channels parallel to the c -axis. β-BaVSi2O7 undergoes short range magnetic order below ∼20 K. Its behavior can best be described as an S = 12 dimer with J/k = -19.0 K, ḡ = 1.87. The fresnoite-type Ba2VSi2O8 is found to be a Curie-Weiss paramagnet down to 4.5 K.