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