Effect of aliovalent doping on the properties of perovskite-like multiferroic formates

Abstract

We report the synthesis, as well as the thermal, dielectric, Raman, IR and luminescence studies of a chromium-doped multiferroic MOF, [(CH₃)₂NH₂][Mn(HCOO)₃] (DMMn). These studies reveal that doping with chromium(III) leads to a lowering of the ferroelectric phase transition temperature T_c. The doping also changes the character of the phase transition from strongly first-order for an undoped sample to a partially diffused one for 3.1% of chromium doping. This behavior resembles the behavior of inorganic ABO₃ perovskite ferroelectrics where doping often leads to a decrease of the T_c and the diffuse character of a phase transition. We also show that the chromium-doped sample exhibits efficient luminescence. Additional studies demonstrated that the [(CH₃)₂NH₂][M^II(HCOO)₃] formates (M^II = Mg, Mn, or Co) may also be doped with other trivalent cations such as Al³⁺, In³⁺, Eu³⁺ or Er³⁺. Doping with these ions also leads to a decrease of the T_c and the diffuse character of the phase transition. Additional optical studies show that the europium-doped DMMn sample also exhibits luminescence properties. Thus our discovery opens up a new and simple route for the synthesis of various multifunctional amine-templated metal formate frameworks with tunable multiferroic and luminescent properties by doping these frameworks with a wide range of trivalent cations.