The fluorite-like LiSm4Mo3O15F ceramics: Synthesis and conductivity

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

“…A weight gain observed in the TG curve of the reduced LiEu 4 Mo 3 O 15− δ F ceramics when heated above 400 °C is associated with thermally activated oxygen uptake from the air. Similar anomaly was also observed for the LiSm 4 Mo 3 O 15− δ F compound 25 but at a lower temperature of about 370 °C. The reason for the rise in temperature at which oxygen begins to absorb from the gas phase is apparently an additional electrostatic repulsion between the O 2− and F − anions in the fluorine-containing compounds as the crystal cell shrinks with decreasing Ln radii.…”

“…Heating above 800 °C for fluorine-containing ceramics would lead to the sublimation of fluorine from the structure, as reported in previous works. 23–25…”

“…A similar effect of color change during oxidation was also observed in previous works. 2,25 Additional heating of the sample in air to 1000 °C leads to the disappearance of the reflection of the impurity phase (Fig. 3, XRD pattern 4).…”

“…At higher temperatures, above 700 °C, the LiEu 4 Mo 3 O 15 F sample loses weight while fluorine sublimates from the ceramics, which was also observed in previous works. 23–25…”

“…A similar phase transition accompanied by a jump in conductivity was also observed for the LiSm 4 Mo 3 O 15 F compound. 25 It is interesting to note that the samarium-containing phase is less hygroscopic than MeLn 4 Mo 3 O 15 F compounds, containing larger rare earth metals, such as lanthanum, praseodymium, or neodymium, and therefore does not contain a fraction of the proton conductivity. In one of the recent works, an accurate X-ray diffraction analysis of the LiLa 4 Mo 3 O 15 F single crystals was carried out at 20 and −183 °C.…”