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