Synthesis of Organic-Inorganic Hybrid Ferroelectric Materials and their Utility in Mechanical Energy Harvesting Applications

Abstract

Multifunctional materials displaying ferroelectric properties are highly desirable for high-technique applications in the areas of energy and electronics. Conventionally, inorganic ceramic oxides are employed as commercial ferroelectric materials. However, they require high-temperature syntheses, high-voltage poling and time-consuming fabrication techniques which impedes their dynamic utilization in certain fields of application. In this regard, ferroelectrics consisting of organic and hybrid organic-inorganic materials are extensively investigated owing to their easy synthesis, light-weight, high flexibility and high polarization values. This thesis highlights the design and synthesis of ferroelectric materials derived from small molecules, based on organo-ammonium, phosphonium and aminophosphazenium salts, and their utility in mechanical energy harvesting applications. By employing flexible ammonium, phosphonium and aminophosphazenium centred scaffolds containing heteroleptic organo and amino substituents, we synthesized several non-centrosymmetric organic and organic-inorganic hybrid assemblies with ferroelectric properties. The substituents around these cationic cores in these assemblies were varied from alkyl to aryl to amino groups and diverse anions such as [CdBr4]2-, [CdCl3]-, [Bi2Br9]3-, I- ions were employed to stabilize their charge-separated structures. By precise molecular tailoring and fine-tuning intermolecular interactions, crystal packing structures ranging from discrete to one- and two-dimensional networks were obtained. Ferroelectric measurement performed on these materials rendered well-resolved hysteresis loops with high remnant polarization values. As the piezoelectric coefficient is directly proportional to the electric polarization, several of these materials with high remnant polarization were employed towards the fabrication of composite piezoelectric nanogenerators with non-piezoelectric polymers such as polydimethylsiloxane and thermoplastic polyurethane. These composite devices demonstrated excellent output electromechanical responses such as output voltage, current- and power-density values under various impact forces and load resistances. All these results underscore a promising advancement for the use of ferroelectric organic-inorganic hybrid materials in the domain of piezoelectric nanogenerators which are envisioned to play a great role in future wearable and self-powered electronics.