Organo and Amino Phosphonium Cation Derived Ferro and Piezoelectric Materials and their Utility in Mechanical Energy Harvesting Applications

Abstract

Multifunctional materials displaying ferroelectricity are very attractive for their utility in high-technique applications in the areas of energy and electronics. Traditionally inorganic ceramic oxides are employed as commercial ferroelectric materials. However, they require high-temperature syntheses, high-voltage poling and the presence of heavy and toxic elements limits their application in certain fields of application. In this regard, ferroelectrics consisting of organic and hybrid organic-inorganic materials have been extensively investigated because of their easy synthesis, light-weight, high flexibility and high polarization values. This presentation will highlight the design and synthesis of small molecules based on organic and organic-inorganic hybrid ferroelectric materials supported by organo and aminophosphonium salts and their utility in mechanical energy harvesting applications. By employing the flexible phosphorus centred scaffolds containing heteroleptic organo and amino substituents, we synthesized organic and hybrid organic-inorganic phosphonium salts in non-centrosymmetric assemblies. The substituents around the cationic phosphorus centre were varied from alkyl to aryl to amino groups in the presence of diverse anions such as Cl‒, Br‒, I‒, PF6‒, BF4‒, ClO4‒, IO4‒, [M(CN)6]3‒(M = Fe, Co) and [Ni(NCS)6]4‒ ions. Ferroelectric measurement on single crystals of several of these materials showed high remnant polarization values. Since the piezoelectric coefficient is directly proportional to the electric polarization, a number of the materials of these series with high remnant polarization were utilized to prepare composite piezoelectric device materials with a non-piezoelectric polymer such as polydimethylsiloxane and thermoplastic polyurethane. These composite devices show excellent output electromechanical responses such as output voltage, output current, current- and power-density values under various impact forces. All these results demonstrate a promising development for the use of piezo and ferroelectric hybrid materials in the domain of mechanical energy harvesters that are envisioned to play a great role in future wearable electronics.