Cu3 O21 Rb Ta7 Benmoussa A, Groult D, Studer F, Raveau B Journal of Solid State Chemistry 41 (1982) 221-226 Intergrowth of Hexagonal Tungsten Bronze and Perovskite-like Structures: The Oxides A Cu3 M7 O21 (A = K, Rb, Cs, Tl; M = Nb, Ta) _cod_database_code 1001218 _database_code_amcsd 0013465 28.11 7.503 7.548 90 90 90 Cmmm atom x y z occ Rb1 0 0 0 Rb2 0 0 .5 Cu1 .173 0 .5 Cu2 .321 0 .5 .5 Cu3 .318 0 0 Cu4 .183 0 0 .5 Ta1 0 .5 .244 Ta2 .1131 .2477 .255 Ta3 .25 .25 .252 O1 .088 0 .248 O2 .274 0 .220 O3 .366 0 .202 O4 .179 .164 .280 O5 .046 .304 .280 O6 .124 .322 .5 O7 .128 .187 0 O8 .236 .323 .5 .5 O9 .238 .186 0 .5 O10 .5 0 .5 O11 .5 0 0