Structure and properties of new ferroelectric crystals M5Nb3OF18(M = NH4, K, Rb)

Abstract By methods of vibration spectroscopy and X-ray analysis ferroelectrics M5Nb3OF18 (M = NH4, K, Rb) have been studied at various temperatures. In Rb5Nb3OF18 crystal, alongside with reversible ferroelectric phase transition (Tc = 600 K), destructive transformation was shown to develop resulting in the destruction of oxofluoroniobate chain in the structure due to the break of Nb—O—Nb bridge bonds and chemical reactions occur.