met all ics , ▁including ▁M g 3 Pr , ▁Cu 3 S b , ▁Fe 3 Si , ▁ ▁and ▁Al Fe 3 , ▁as ▁well ▁as ▁by ▁the ▁hyd ride ▁La H 3 . 0 . ▁The ▁unit ▁cell ▁is ▁face - center ed ▁cub ic ▁with ▁Bi ▁at ▁the ▁face ▁cent ers ▁and ▁vertices , ▁and ▁F ▁at ▁the ▁oct ah ed ral ▁site ▁( mid - ed ges , ▁center ), ▁and ▁t etra hed ral ▁sites ▁( cent ers ▁of ▁the ▁ 8 ▁sub ▁cub es ) ▁- ▁thus ▁the ▁primitive ▁cell ▁contains ▁ 4 ▁Bi ▁and ▁ 1 2 ▁F . ▁Alternatively , ▁with ▁the ▁unit ▁cell ▁shift ed ▁( 1 / 4 , 1 / 4 , 1 / 4 ) ▁the ▁description ▁can ▁be ▁of ▁a ▁f cc ▁cell ▁with ▁face , ▁edge , ▁corner , ▁and ▁cent ers ▁filled ▁with ▁F , ▁and ▁half ▁( 4 ▁of ) ▁the ▁oct ant ▁cent ers ▁with ▁F , ▁the ▁other ▁half ▁with ▁Bi ▁( each ▁oct ant ▁type ▁t etra hed r ally ▁arranged ). ▁The ▁edge ▁length ▁of ▁the ▁Bi F 3 ▁cell ▁is ▁ 0 . 5 8 5 3 ▁n m . ▁▁ β - Bi F 3 ▁has ▁the ▁Y F 3 ▁structure ▁where ▁the ▁b ism uth ▁atom ▁has ▁dist orted ▁ 9 ▁coord ination , ▁tr ic apped ▁trig onal ▁pr ism . ▁This ▁structure ▁is ▁generally ▁considered ▁to ▁be ▁ion ic , ▁and ▁contrast s ▁with ▁flu or ides