data_global _chemical_name_mineral 'Belkovite' loop_ _publ_author_name 'Choisnet J' 'Nguyen N' 'Groult D' 'Raveau B' _journal_name_full 'Materials Research Bulletin' _journal_volume 11 _journal_year 1976 _journal_page_first 887 _journal_page_last 894 _publ_section_title ; De nouveaux oxydes a reseau forme d'octahedres NbO6 (TaO6) et de groupes Si2O7: Les phases A3Ta6Si4O26 (A = Ba,Sr) et K6M6Si4O26 (M = Nb,Ta) ; _database_code_amcsd 0014242 _chemical_compound_source 'Synthetic' _chemical_formula_sum 'Ba3 Nb6 Si4 O26' _cell_length_a 8.981 _cell_length_b 8.981 _cell_length_c 7.840 _cell_angle_alpha 90 _cell_angle_beta 90 _cell_angle_gamma 120 _cell_volume 547.641 _exptl_crystal_density_diffrn 4.541 _symmetry_space_group_name_H-M 'P -6 2 m' loop_ _space_group_symop_operation_xyz 'x,y,z' '-x,-x+y,z' '-x+y,-x,-z' 'y,x,-z' '-y,x-y,z' 'x-y,-y,z' 'x,y,-z' '-x,-x+y,-z' '-x+y,-x,z' 'y,x,z' '-y,x-y,-z' 'x-y,-y,-z' loop_ _atom_site_label _atom_site_fract_x _atom_site_fract_y _atom_site_fract_z _atom_site_U_iso_or_equiv Ba 0.59300 0.00000 0.50000 ? Nb 0.23800 0.00000 0.23900 ? Si 0.33333 0.66667 0.20300 0.00317 O1 0.33333 0.66667 0.00000 0.00773 O2 0.27300 0.00000 0.00000 0.00874 O3 0.81900 0.00000 0.23600 0.00937 O4 0.48900 0.18300 0.28400 0.00608 O5 0.22700 0.00000 0.50000 0.00861