Effect of Sodium and Fluorine Co‐Doping on the Properties of Fluorite‐Like Rare‐Earth Molybdates of Nd5Mo3O16 Type

Fluorite‐like oxyfluorides NaLn 4 Mo 3 O 15 F (Ln = La, Pr, Nd), which relate to the Nd 5 Mo 3 O 16 structural type, were obtained by solid‐phase synthesis in the air. Codoping of the Nd 5 Mo 3 O 16+ δ family with sodium and fluorine led to the appearance of a piezoelectric effect and a reversible phase transition in oxyfluorides, accompanied by a jump in the conductivity and an anomaly of the permittivity of the ferroelectric type. It is assumed that the compounds NaLn 4 Mo 3 O 15 F in contrast to Nd 5 Mo 3 O 16+ δ , which possess mixed oxide‐ion/electronic interstitial conductivity, can have oxygen conductivity of vacancy type. The highest conductivity offered by these materials is 3.2 × 10 –2 S/cm at 700 °C. NaLn 4 Mo 3 O 15 F compounds were found to be hygroscopic and can be considered as potential proton conductors.