Internal Friction Study of the Rare Earth Ion Substituted Fast Oxide-Ion Conductors (La_1-Χre_Χ)₂Mo₂O₉ (Re=Nd, Gd)

The relaxation and phase transition behaviors of rare-earth ion substituted fast oxide-ion conductors (La 1- x Re x ) 2 Mo 2 O 9 (Re=Nd, Gd) were investigated by internal friction (IF) measurement in the temperature range 300 K - 950 K. Three different IF peaks (labeled as P L , P H , and P G , respectively) were observed in the rare-earth ion doped La 2 Mo 2 O 9 samples. Peak P L corresponds to short diffusion processes of oxygen ions among different oxygen vacancy sites. Peak P H is associated with the static/dynamic disorder transition in oxygen ion distribution. Peak P G is a newly discovered peak embodying phase transition-like characteristics and is suggested to be related to order-disorder transition associated with the rearrangement of La/ Re sub-lattice.