The combination 3 wherein said rare earth material is selected from {HEAD ~ the group} consisting of {TAIL ~ yttrium}, lanthanum and hafnium 
consisting of
The combination 3 wherein said rare earth material is selected from { HEAD ~ the group } consisting of { TAIL ~ yttrium } , lanthanum and hafnium
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH