Dielectric and pyroelectric properties of TGS-polystyrene composites

Abstract

A composite of triglycine sulphate (TGS) and polystyrene has been fabricated in a multilayer pattern with 2–2 connectivity made up of alternating layers of polystyrene and TGS powder. Samples with TGS powders of varying particle size, ranging from less than 75 μm to more than 400 μm were prepared in the form of thin sheets (2.0 cm × 1.5 cm × 0.15 cm). Samples with same weight percentage (70 to 75%) of TGS, but different particle size, were chosen for dielectric and pyroelectric studies in the ferro- and paraelectric phases. The dielectric constant and loss have been measured in the frequency range of 0.1 to 100 KHz and the pyroelectric current measurements were made by the Byer and Roundy direct method.

The magnitude of dielectric constant (ϵ′) and pyroelectric coefficient Py show an increase with increasing particle size and the room temperature values for the biggest particle size are [ϵ′ = 8.3] and Py = 0.6 × 10⁻¹⁰ C cm⁻² K⁻¹. Anomalies in ϵ′ and pyroelectric coefficient, indicating the existence of ferroelectricity were observed even for the composites with the lowest particle size of TGS (< 75 μm). A dielectric dispersion in the frequency range 0.1 to 100 KHz and the particle size dependence of pyroelectric coefficient and dielectric constant can be accounted for by assuming non-ferroelectric surface layers at the boundaries of TGS crystallites. The responsivity of TGS-Polystyrene composites for infrared detection has been compared with those of single crystals, hot pressed TGS powders and composites employing other ferroelectrics. The decrease in pyroelectric coefficient with particle size is compensated to some extent by the decrease in dielectric constant, such that responsivity of these composites does not show any marked dependence on particle size.