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

Abstract

We show that doping of multiferroic formates with various trivalent cations is a new route for the synthesis of tunable luminescent multiferroics.

Abstract

We report the synthesis, as well as the thermal, dielectric, Raman, IR and luminescence studies of a chromium-doped multiferroic MOF, [(CH ₃) ₂NH ₂][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 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 [(CH ₃) ₂NH ₂][M ^II(HCOO) ₃] formates (M ^II = Mg, Mn, or Co) may also be doped with other trivalent cations such as Al ³⁺, In ³⁺, Eu ³⁺ or Er ³⁺. 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.