wherein {HEAD ~ the metal oxide} is selected from {TAIL ~ the group} consisting of: aluminum oxide, yttrium oxide, zirconium oxide and chromium oxide, and 
is selected from
wherein { HEAD ~ the metal oxide } is selected from { TAIL ~ the group } consisting of : aluminum oxide , yttrium oxide , zirconium oxide and chromium oxide , and
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH