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