Crystal growth and characterization of tetragonal tungsten bronze FerroNiobates Ba_2LnFeNb_4O_(15)

摘要

Tetragonal Tungsten Bronze Ferroelectrics (TTB) are currently revisited for the elaboration of new multifunctional materials. Recent studies on Ba_2LnFeNb_4O_(15) ceramics (Ln = Nd, Sm and Eu) demonstrated that these materials display both ferroelectric and ferromagnetic behaviors at room temperature due to the presence of barium hexaferrite as a secondary phase. In this paper, we report for the first time the growth of Ba_2LnFeNb_4O_(15) single crystals (Ln=La, Pr, Nd, Sm and Eu) from high temperature solution using LiBO_2 flux. Inclusion free millimeter-sized single crystals were successfully grown. Structural and dielectric characterizations were performed and chemical analysis confirmed that the TTB matrix is reluctant to accommodate small rare earth as it was observed for ceramics. A paramagnetic behavior was observed for all compositions, which corroborates the composite nature of the TTB ceramic multiferroics at room temperature, while dielectric measurements on Ln=La and Pr crystals confirmed their relaxor behavior.