translate "percent" in chinese 百分之 or 百分比? is there one by the two words above usually used for " percent " ?  

or is it usual  to use any of them ?  

wenlin software  gives 百分比 as percent.  

mdbg dictionary on line gives 百分之   :-)
Matter of taste. You want prefix style, use 百分比, as in 五个百分比. Suffix style, use 百分之, as in 百分之五.

百分之 is a sentence pattern, and requires a number. 百分比 is a noun, and also means percentage on its own.