Some sign it ionised, creating spark (8)
I believe the answer is:
ignition
'spark' is the definition.
(a spark might ignite something)
'some sign it ionised' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'IGNITION' is hidden within 'sign it ionised'.
'creating' is the link.
(Other definitions for ignition that I've seen before include "Act of starting a fire" , "Process of starting car" , "Act of lighting burner" , "Process of starting fire" , "Point at which combustion occurs" .)