A new phase of dibarium copper disilicate, b-Ba2CuSi2O7, was obtained by the solid-state reaction. Crystal data: Mr = 506.4, tetragonal, P421m, a = 8.284(2), c = 5.313(3) ? V = 364.6(4) ?, Z = 2, Dc = 4.61 g/cm3, l(MoKa) = 0.71703 ? ?= 13.91 mm-1, F(000) = 450 and T = 293(2) K; the final R = 0.0343, wR = 0.0382 and S = 1.02 for 512 observed reflections (I > 3s(I)) refined by 34 variables. The compound was characterized by a layered structure composed of CuO4 tetrahedra and Si2O7 anions with the Ba cations filling the cavities between the layers. The building blocks of the present structure are similar to those in the a-Ba2CuSi2O7, but the linkage of CuO4 tetrahedra and Si2O7 anions is significantly different. In particular, the double-tetrahedral anions of Si2O76- form an orthogonal arrangement in the present structure, in contrast to the parallel arrangement reported in the a-Ba2CuSi2O7. Crystal data: Mr = 506.4, tetragonal, P421m, a = 8.284 (2), c = 5.313 (3)? V = 364.6 (3) A new phase of dibarium copper disilicate, b- Ba2CuSi2O7, was obtained from the solid- The final R = 0.0343, F (000) = 450 and T = 293 (2) K; Z = 2; Dc = 4.61 g / cm3; MoKa = 0.71703? = 13.91 mm- The compound was characterized by a layered structure composed of CuO 4 tetrahedra and Si 2 O 7 anions with the Ba cations filling the cavities between the layers. The building blocks of the present structures are similar to those of a-Ba2CuSi2O7, but the linkage of CuO4 tetrahedra and Si2O7 anions is significantly different. In particular, the double-tetrahedral anions of Si2O76- form an orthogonal arrangement in the present structure, in contrast to the parallel arrangement reported in the a-Ba2CuSi2O7.