▁structure . ▁ ▁Ar - T ON ▁Under ▁pressure ▁arg on ▁inser ts ▁into ▁ze ol ite . ▁Arg on ▁has ▁an ▁atomic ▁radius ▁of ▁ 1 . 8   Å , ▁so ▁it ▁can ▁insert ▁into ▁por es ▁if ▁they ▁are ▁big ▁enough . ▁Each ▁unit ▁cell ▁of ▁the ▁T ON ▁ze ol ite ▁can ▁contain ▁up ▁to ▁ 5 ▁atoms ▁of ▁arg on , ▁compared ▁to ▁ 1 2 ▁of ▁ne on . ▁Arg on ▁inf used ▁T ON ▁ze ol ite ▁( Ar - T ON ) ▁is ▁more ▁compress ible ▁than ▁Ne - T ON ▁as ▁the ▁un occup ied ▁por es ▁become ▁elli pt ical ▁under ▁increased ▁pressure . ▁When ▁Ar - T ON ▁is ▁brought ▁to ▁atmos pher ic ▁pressure , ▁the ▁arg on ▁only ▁des or bs ▁slowly , ▁so ▁that ▁some ▁remains ▁in ▁the ▁solid ▁without ▁external ▁pressure ▁for ▁a ▁day . ▁ ▁Nick el ▁arg ide ▁At ▁ 1 4 0   G Pa ▁and ▁ 1 5 0 0 K ▁nick el ▁and ▁arg on ▁form ▁an ▁al loy , ▁Ni Ar . ▁Ni Ar ▁is ▁stable ▁at ▁room ▁temperature ▁and ▁a ▁pressure ▁as ▁low ▁as ▁ 9 9   G Pa . ▁It ▁has ▁a ▁face - cent red ▁cub ic ▁( f cc ) ▁structure . ▁The ▁comp ound ▁is ▁met all ic . ▁Each ▁nick el ▁atom ▁los es ▁ 0 . 2 ▁electrons ▁to ▁an ▁arg on ▁atom ▁which ▁is ▁thereby ▁an ▁ox id ant . ▁This ▁contrast s