A Strategy to Enhance the Ferroelectric Behavior of MOF-802(Hf) via Doping Zr4+ Ions

MOF ferroelectrics, as a crucial member of molecular ferroelectrics, have shown intriguing advantages owing to the designability of structures and tunability of physicochemical properties, which make them an appealing group of ferroelectric materials. However, the weak ferroelectric property still is a huge challenge for further development. Here, a series of Zr-doped MOF-802(Hf)s were successfully synthesized through doping Zr4+ ions into the parent MOF-802(Hf) to improve ferroelectric properties. The well-shaped P-E hysteresis loops of Zr-doped MOF-802(Hf)s illustrate their ferroelectricity, and ferroelectric properties are effectively enhanced compared with the parent MOF-802(Hf). What's more, remanent polarization reaches 0.511 μC/cm2 when the concentration of Zr4+ ions is 5%, which is 5 times higher than that of the parent MOF-802(Hf) and is on par with some perovskite ferroelectrics. The increased ferroelectric performance is attributed to the enhanced polarity of the whole structure triggered by lattice distortion when Hf4+ ions of the parent MOF-802(Hf) are substituted by Zr4+ ions. As far as we know, this is the first report on Hf-MOF exhibiting improved ferroelectric behaviors through doping metal ions into lattice nodes. This work demonstrates that introducing the second metal ions into lattice nodes of MOFs is an efficacious approach for exploiting MOF ferroelectrics with superior performance.