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

Abstract

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 [a]

Fluorite‐like LixLn5–xMo3O16.5–1.5xFx (Ln = La, Pr, Nd) compounds isostructural with Nd5Mo3O16

“…Note that the amount of vaporized fluorine at Ln = Nd was the same as that at Ln = La, suggesting that there was a sufficient amount of fluorine in the ceramics, which is consistent with the Na analog 25 …”

“…Given that, after substitution of fluorine on the oxygen site and lithium on the lanthanide‐earth site, there may be no interstitial oxygen, we assume that appropriate interstices can be filled with water as a result of hydration. Indeed, the NaLn 4 Mo 3 O 15 F compounds studied previously 25 were found to be hygroscopic, with water uptake during hydration and water vaporization during heating.…”

“…At the same time, the bulk of the ceramic contained an appropriate amount of F according to TG data (Section 3.2). Note that for the sample NaNd 4 Mo 3 O 15 F, EDX showed an acceptable amount of fluorine with some lack of neodymium (Na 1.0±0.2 Nd 3.4±0.4 Mo 3 O 16±3 F 1.0±0.4 ) 25 . The elemental X‐ray maps were rather uniform, suggesting that there was neither sublimation nor a second phase.…”

“…The properties of the MeLn 4 Mo 3 O 15 F compounds have not been studied previously. There is still only one report concerned with the properties of the NaLn 4 Mo 3 O 15 F (Ln = La, Pr, Nd) compounds 25 . They were shown to exhibit a piezoelectric response at room temperature and undergo a reversible first‐order ferroelectric phase transition near 600°C, where their conductivity rises sharply.…”

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

“…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…”