Because of its good insulating properties and low GWP（greenhouse effect potential）value

c-C

4

F

8

gas has attracted wide attention.However

the effects of O

2

on the breakdown and breakdown Characteristics of c-C

4

F

8

have not been studied yet.Consequently

we compared the frequency breakdown characteristics and

self-recovery characteristics of c-C

4

F

8

/N

2

under different proportions of O

2

by experiments.Moreover

we analyzed the composition of the precipitates and the composition of the gas decomposition products

and discussed the decomposition mechanism of c-C

4

F

8

based on density functional theory.The results show that the frequency breakdown voltage of c-C

4

F

8

/N

2

will be significantly reduced when O

2

is added.Compared with the c-C

4

F

8

/N

2

in the absence of O

2

the self recovery characteristics of mixed gas containing 3%O

2

is greatly reduced.After the breakdown of c-C

4

F

8

/N

2

mixed gas containing O

2

the surface of the electrode precipitates a black powdery substance whose main component is COF.The black powder consists of the elemental C and the oxygen fluoride of C.Meanwhile

O

2

can contribute to the decomposition of c-C

4

F

8

decomposing c-C

4

F

8

into more CF

4

and C

2

F

4

etc.

additionally producing a large number of toxic and corrosive COF

2

gas.Considering insulation characteristics and decomposition characteristics

c-C

4

F

8

should not be mixed with dry air and the oxygen content in c-C

4

F

8

mixture should be strictly controlled in the actual use.