TKWB-Type Lead-Free Oxyfluoride Relaxors Derived from Ba2NaNb5O15

Abstract

Three solid solutions were prepared from Ba 2 NaNb 5 O 15 by coupled cationic and/or anionic substitutions: Ba 2--x Na 1+x (Nb 5--x W x )O 15, Ba 2--x Na 1+x Nb 5 O 15--x F x and Ba 2 NaNb 5--x Ti x O 15--x F x . They crystallize with a TKWB-type structure. In the case of oxyfluoride compositions, large frequency range dielectric studies performed on ceramics demonstrated a relaxor behavior. The greater the substitution rate, the higher the relaxor corresponding characteristics. Such a behavior is in agreement with the cationic disorder of Ba 2+ and Na + in the same crystallographic site of BaNa 2 Nb 5 O 14 F. In addition, the following transition sequence was obtained: relaxor ! ferroelectric ! paraelectric. Such ceramics constitute a new family of lead-free relaxor compositions with TKWB structure and can be used in environmental-friendly applications.

Solid‐State Chemistry and Non‐Linear Properties of Tetragonal Tungsten Bronzes Materials

“…This is also the case with the Ba 2 NaNb 5 O 15 -BaNa 2 Nb 5 O 14 F system; for compositions close to the oxide, the behaviour is ferroelectric, while it becomes relaxor when the fluorine rate and thus the sodium rate is sufficiently high (Fig. 4) [34]. The frequency dependence of the permittivities of a ceramic with a composition BaNa 2 Nb 5 O 14 F clearly displays a frequency relaxation at 77 K, while it disappears at 300 K, i.e.…”