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

We report the synthesis, as well as the thermal, dielectric, Raman, IR and luminescence studies of a chromium-doped multiferroic MOF, [(CH3)(2)NH2][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 ABO(3) perovskite ferroelectrics where doping often leads to a decrease of the Tc 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)(2)NH2][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 Tc 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.