TKWB-type lead-free oxyfluoride relaxors derived from Ba2NaNb5O15

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 crystal-lize 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.