Dielectric Tunability, Expanding the Function of Metal-Organic Frameworks

Above room-temperature dielectric tunability is observed in the metal-organic frameworks (MOFs) [NH2(CH3)(2)](n)[(FeFeII)-Fe-III(HCOO)(6)](n) (1) and [NH2(CH3)(2)](n)[(FeFe(1-x)NixII)-Fe-III-Ni-II(HCOO)(6)](n) (x=0.64-0.69) (2). The relative tunability (defined as [E-(0) - E-(E)]/E((0))x100%=E/E((0))x100%) values for 1 are up to 35% (at 410K) for E perpendicular to c and 21% (at 380K) for E||c, while these for 2 are 14% for E perpendicular to c and 11.5% for E||c. Investigation on the mechanism of the dielectric tunability in 1 and 2 reveals that the activation energy for the electron hopping between two adjacent metal ions and the magnetic exchange interaction play a key role in the dielectric tunability of these materials.