{HEAD ~ Spinel type MgAl2O4} is substituted into a basic spinel structure for {TAIL ~ structural stability} 
{ HEAD ~ Spinel type MgAl2O4 } is substituted into a basic spinel structure for { TAIL ~ structural stability }
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL