The fluorite-like Ln₅Mo₃O₁₆₊ family extension: LiLn₄Mo₃O₁₅F (Ln = Eu, Gd, or Dy) ceramics

Fluorine-containing rare earth compounds of the LiLn(4)Mo(3)O(15)F (Ln = Eu, Gd, or Dy) composition have been obtained using solid-phase synthesis in vacuum-sealed quartz ampoules. It was found that only LiEu4Mo3O15F samples are isostructural to cubic Ln(5)Mo(3)O(16) (Ln = La-Gd) molybdates with a fluorite-like structure. Luminescence, hygroscopic, and electrophysical characteristics of the LiEu4Mo3O15F phase were studied for the first time. The double replacement of europium with lithium and oxygen with fluorine leads to the appearance of a reversible phase transition accompanied by a jump in conductivity by 2 orders of magnitude. The conductivity of the LiEu4Mo3O15F compound exceeds the value of 10(-2) S cm(-1) at 700(degrees)C. A relationship between the size of the Ln cation and the hygroscopic and conductive properties of LiLn(4)Mo(3)O(15)F compounds has been established: as the lanthanide radius decreases, the compounds lose their ability to absorb water and transfer protons.