Large Piezoelectricity in a Dynamic Metal-Organic Framework With Negative Linear Compressibility

Piezoelectric metal-organic frameworks (MOFs) have recently gained increasing attention for their potential in energy harvesting and sensing applications. However, their performance still lags behind that of conventional ceramics and polymers, mainly due to a lack of effective design and screening strategies. Here, we report that the negative linear compressibility (NLC) enhances piezoelectricity in a dynamic MOF, Ni(PyC)₂·DMF (Pyc = 4-pyridine carboxylate, DMF = N,N-dimethylformamide, denoted as IISERP-MOF2). The NLC along its crystallographic b-axis causes significant strain along the c-axis, resulting in a high piezoelectric voltage coefficient, g₃₃, of 859.4 × 10^-3 Vm/N, which is 75.6 times greater than BaTiO₃ and 2.8 times that of polyvinylidene fluoride (PVDF). Importantly, this principle has also been confirmed in two other MOFs and a molecular framework exhibiting NLC. Devices made with MOF/polymer composites demonstrate excellent efficiency in energy harvesting and underwater ultrasonic sensing, achieving 1.4 and 2.4 times the performance of PbZr_xTi_1-xO₃ and PVDF devices, respectively. This paradigm reveals that large piezoelectricity can be found in a wide range of NLC crystals with noncentrosymmetry.