The First Nickel(II)-Nitrite-Based Molecular Perovskite Ferroelectric.

The X-site ion in organic-inorganic hybrid ABX(3) perovskites (OHPs) varies from halide ion to bridging linkers like HCOO-, N-3(-), NO2-, and CN-. However, no nitrite-based OHP ferroelectrics have been reported so far. Now, based on non-ferroelectric [(CH3)(4)N][Ni(NO2)(3)], through the combined methodologies of quasi-spherical shape, hydrogen bonding functionality, and H/F substitution, we have successfully synthesized an OHP ferroelectric, [FMeTP][Ni(NO2)(3)] (FMeTP=N-fluoromethyl tropine). As an unprecedented nitrite-based OHP ferroelectric, the well-designed [FMeTP][Ni(NO2)(3)] undergoes the ferroelectric phase transition at 400K with an Aizu notation of 6/mmmFm, showing multiaxial ferroelectric characteristics. This work is a great step towards not only enriching the molecular ferroelectric families but also accelerating the potential practical applications.