Fluorite‐like Li x Ln 5– x Mo 3 O 16.5–1.5 x F x (Ln = La, Pr, Nd) compounds isostructural with Nd 5 Mo 3 O 16

Li x Ln 5– x Mo 3 O 16.5–1.5 x F x (0.8 ≤  x  ≤ 1.4 (Ln = La), 0.4 ≤  x  ≤ 1 (Ln = Pr), 0.6 ≤  x  ≤ 1 (Ln = Nd)) solid solutions on the Ln 5 Mo 3 O 16 –LiLn 4 Mo 3 O 15 F joins of the Ln 2 O 3 –MoO 3 –LiF ternary systems, similar to the fluorite‐related cubic compound Nd 5 Mo 3 O 16 , have been prepared by solid‐state reactions. Substitutions of lithium on the rare‐earth site and fluorine on the oxygen site have been shown to lead to a reversible phase transition accompanied by an anomaly in permittivity and a jump in conductivity by one and half orders of magnitude. In a wet atmosphere, the Li x Ln 5– x Mo 3 O 16.5–1.5 x F x compounds may have proton conductivity.