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