From molecular ferroelectrics to intelligent sensors: β-phase engineering of PVDF by a discrete Ni-Tb complex for...

Growing environmental and ecological concerns associated with conventional energy-harvesting technologies have accelerated the search for sustainable alternatives such as piezoelectric nanogenerators (PENGs). A key challenge in this domain is the stabilization of the electroactive β-phase of PVDF, which is very important for achieving high piezoelectric performance. Although several advanced methods exist, inducing the polar β-phase under mild conditions using molecular additives remains an emerging and promising strategy. In this work, we demonstrate that a discrete inorganic complex [NiTb(L)(NO₃)₃] (NiTb; where H₂L = 6,6'-((1E,1'E)-(((1R,2S)-1,2-diphenylethane-1,2-diyl)bis(azaneylylidene))bis(methaneylylidene)) bis(2-methoxyphenol)), crystallized in a non-centrosymmetric polar space group, effectively facilitates the formation of the electroactive β-PVDF phase. Among the fabricated devices with varying NiTb loadings (3-10 wt%), the 7 wt% composition shows a high piezoelectric coefficient (d₃₃ ≈ 32 pm V^-1), open-circuit voltage (∼15 ± 1.5 V), short-circuit current (∼0.4 ± 0.04 µA), and power density (1.77 ± 0.16 µW cm^-2). Furthermore, integration with an AI/ML framework based on ANN-LSTM models enables real-time classification of ten distinct human activities with 97% accuracy, highlighting its potential for next-generation wearable and intelligent electronic systems.