Pyroelectric figures of merit and associated properties of LiTaO3/poly vinylidene difluoride nanocomposites for thermal/infrared sensing

Abstract

Polymer–ceramic nanocomposites with good pyroelectric properties are proposed as promising materials for the detection and measurement of thermal waves, including infrared radiation. They possess simultaneously the advantages of high detection sensitivity of the ceramic as well as the flexibility and light weight of the polymer. Selection of the appropriate ceramic additive and the polymer matrix is the key to the success for the development of the best material for any application. The aim of this work is to develop highly sensitive, at the same time flexible, polymer-nanocomposites for pyroelectric detector applications by dispersing the well known pyroelectric material, lithium tantalate, LiTaO3, in nanocrystalline form, in an inherently pyroelectric host polymer matrix, polyvinylidene difluoride (PVDF). LiTaO3 nanoparticles are synthesised and dispersed in PVDF at varying volume fractions, and composite materials cast in the form of films for measurements. The β-phase of PVDF is confirmed from powder XRD, FT-IR and DSC measurements. The dielectric properties, shore D hardness and pyroelectric coefficients of the cast films are measured. The thermal conductivity and specific heat capacity of the films are measured following a photothermal technique. From these data the pyroelctric figures of merit of the composite films have been determined and values compared with that of pure PVDF film. It is found that, in general, the pyroelectric figure of merit increases with concentration of LiTaO3; however, it is at the expense of mechanical flexibility of the material. This paper aims at providing guidelines to strike the right balance between detection sensitivity and material flexibility (or mouldability), depending on the application.