 Ytterbium reacts with oxygen to form ytterbium ( III ) oxide ( <unk> ) , which crystallizes in the " rare @-@ earth C @-@ type sesquioxide " structure which is related to the fluorite structure with one quarter of the anions removed , leading to ytterbium atoms in two different six coordinate ( non @-@ octahedral ) environments . Ytterbium ( III ) oxide can be reduced to ytterbium ( II ) oxide ( <unk> ) with elemental ytterbium , which crystallizes in the same structure as sodium chloride . 
