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